diff --git a/doc/Clusters_from_Scratch/en-US/Book_Info.xml b/doc/Clusters_from_Scratch/en-US/Book_Info.xml index e436c02aac..4eb6943f70 100644 --- a/doc/Clusters_from_Scratch/en-US/Book_Info.xml +++ b/doc/Clusters_from_Scratch/en-US/Book_Info.xml @@ -1,67 +1,67 @@ %BOOK_ENTITIES; ]> Clusters from Scratch Creating Active/Passive and Active/Active Clusters on Fedora Pacemaker 1.1 8 - 0 + 1 The purpose of this document is to provide a start-to-finish guide to building an example active/passive cluster with Pacemaker and show how it can be converted to an active/active one. The example cluster will use: &DISTRO; &DISTRO_VERSION; as the host operating system Corosync to provide messaging and membership services, Pacemaker to perform resource management, DRBD as a cost-effective alternative to shared storage, GFS2 as the cluster filesystem (in active/active mode) Given the graphical nature of the Fedora install process, a number of screenshots are included. However the guide is primarily composed of commands, the reasons for executing them and their expected outputs. diff --git a/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt b/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt index ca81b217f7..7ed4f808b7 100644 --- a/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt +++ b/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt @@ -1,164 +1,26 @@ = Read-Me-First = == The Scope of this Document == Computer clusters can be used to provide highly available services or resources. The redundancy of multiple machines is used to guard against failures of many types. This document will walk through the installation and setup of simple clusters using the &DISTRO; distribution, version &DISTRO_VERSION;. The clusters described here will use Pacemaker and Corosync to provide resource management and messaging. Required packages and modifications to their configuration files are described along with the use of the Pacemaker command line tool for generating the XML used for cluster control. Pacemaker is a central component and provides the resource management required in these systems. This management includes detecting and recovering from the failure of various nodes, resources and services under its control. When more in depth information is required and for real world usage, please refer to the http://www.clusterlabs.org/doc/[Pacemaker Explained] manual. -== What Is Pacemaker? == - -Pacemaker is a cluster resource manager. - -It achieves maximum availability for your cluster services -(aka. resources) by detecting and recovering from node- and -resource-level failures by making use of the messaging and membership -capabilities provided by your preferred cluster infrastructure (either -http://www.corosync.org/[Corosync] or -http://linux-ha.org/wiki/Heartbeat[Heartbeat]). - -Pacemaker's key features include: - - * Detection and recovery of node and service-level failures - * Storage agnostic, no requirement for shared storage - * Resource agnostic, anything that can be scripted can be clustered - * Supports fencing (aka. STONITH) for ensuring data integrity - * Supports large and small clusters - * Supports both quorate and resource-driven clusters - * Supports practically any redundancy configuration - * Automatically replicated configuration that can be updated from any node - * Ability to specify cluster-wide service ordering, colocation and anti-colocation - * Support for advanced service types - ** Clones: for services which need to be active on multiple nodes - ** Multi-state: for services with multiple modes (eg. master/slave, primary/secondary) - * Unified, scriptable, cluster management tools. - -== Pacemaker Architecture == - -At the highest level, the cluster is made up of three pieces: - - * Non-cluster-aware components. These pieces - include the resources themselves; scripts that start, stop and - monitor them; and a local daemon that masks the differences - between the different standards these scripts implement. - - * Resource management. Pacemaker provides the brain that processes - and reacts to events regarding the cluster. These events include - nodes joining or leaving the cluster; resource events caused by - failures, maintenance and scheduled activities; and other - administrative actions. Pacemaker will compute the ideal state of - the cluster and plot a path to achieve it after any of these - events. This may include moving resources, stopping nodes and even - forcing them offline with remote power switches. - - * Low-level infrastructure. Projects like Corosync, CMAN and - Heartbeat provide reliable messaging, membership and quorum - information about the cluster. - -When combined with Corosync, Pacemaker also supports popular open -source cluster filesystems. -footnote:[Even though Pacemaker also supports Heartbeat, the filesystems need -to use the stack for messaging and membership, and Corosync seems to be -what they're standardizing on. Technically, it would be possible for them to -support Heartbeat as well, but there seems little interest in this.] - -Due to past standardization within the cluster filesystem community, -cluster filesystems make use of a common distributed lock manager, which makes -use of Corosync for its messaging and membership capabilities (which nodes -are up/down) and Pacemaker for fencing services. - -.The Pacemaker Stack -image::images/pcmk-stack.png["The Pacemaker stack",width="10cm",height="7.5cm",align="center"] - -=== Internal Components === - -Pacemaker itself is composed of five key components: - - * Cluster Information Base (CIB) - * Cluster Resource Management daemon (CRMd) - * Local Resource Management daemon (LRMd) - * Policy Engine (PEngine or PE) - * Fencing daemon (STONITHd) - -.Internal Components -image::images/pcmk-internals.png["Subsystems of a Pacemaker cluster",align="center",scaledwidth="65%"] - -The CIB uses XML to represent both the cluster's configuration and -current state of all resources in the cluster. The contents of the CIB -are automatically kept in sync across the entire cluster and are used -by the PEngine to compute the ideal state of the cluster and how it -should be achieved. - -This list of instructions is then fed to the Designated -Controller (DC). Pacemaker centralizes all cluster decision making by -electing one of the CRMd instances to act as a master. Should the -elected CRMd process (or the node it is on) fail, a new one is -quickly established. - -The DC carries out the PEngine's instructions in the required order by -passing them to either the Local Resource Management daemon (LRMd) or -CRMd peers on other nodes via the cluster messaging infrastructure -(which in turn passes them on to their LRMd process). - -The peer nodes all report the results of their operations back to the -DC and, based on the expected and actual results, will either execute -any actions that needed to wait for the previous one to complete, or -abort processing and ask the PEngine to recalculate the ideal cluster -state based on the unexpected results. - -In some cases, it may be necessary to power off nodes in order to -protect shared data or complete resource recovery. For this, Pacemaker -comes with STONITHd. - -STONITH is an acronym for Shoot-The-Other-Node-In-The-Head and is -usually implemented with a remote power switch. - -In Pacemaker, STONITH devices are modeled as resources (and configured -in the CIB) to enable them to be easily monitored for failure, however -STONITHd takes care of understanding the STONITH topology such that -its clients simply request a node be fenced, and it does the rest. - -== Types of Pacemaker Clusters == - -Pacemaker makes no assumptions about your environment. This allows it -to support practically any -http://en.wikipedia.org/wiki/High-availability_cluster#Node_configurations[redundancy -configuration] including Active/Active, Active/Passive, N+1, N+M, -N-to-1 and N-to-N. - -.Active/Passive Redundancy -image::images/pcmk-active-passive.png["Active/Passive Redundancy",width="10cm",height="7.5cm",align="center"] - -Two-node Active/Passive clusters using Pacemaker and DRBD are a -cost-effective solution for many High Availability situations. - -.Shared Failover -image::images/pcmk-shared-failover.png["Shared Failover",width="10cm",height="7.5cm",align="center"] - -By supporting many nodes, Pacemaker can dramatically reduce hardware -costs by allowing several active/passive clusters to be combined and -share a common backup node - -.N to N Redundancy -image::images/pcmk-active-active.png["N to N Redundancy",width="10cm",height="7.5cm",align="center"] - -When shared storage is available, every node can potentially be used -for failover. Pacemaker can even run multiple copies of services to -spread out the workload. +include::../../shared/en-US/pacemaker-intro.txt[] diff --git a/doc/Clusters_from_Scratch/en-US/Clusters_from_Scratch.ent b/doc/Clusters_from_Scratch/en-US/Clusters_from_Scratch.ent index eafd2819e2..5a675ebd55 100644 --- a/doc/Clusters_from_Scratch/en-US/Clusters_from_Scratch.ent +++ b/doc/Clusters_from_Scratch/en-US/Clusters_from_Scratch.ent @@ -1,6 +1,6 @@ - + diff --git a/doc/Clusters_from_Scratch/en-US/Revision_History.xml b/doc/Clusters_from_Scratch/en-US/Revision_History.xml index 0df7bbc577..03d367ea73 100644 --- a/doc/Clusters_from_Scratch/en-US/Revision_History.xml +++ b/doc/Clusters_from_Scratch/en-US/Revision_History.xml @@ -1,62 +1,68 @@ %BOOK_ENTITIES; ]> Revision History 1-0 Mon May 17 2010 AndrewBeekhofandrew@beekhof.net Import from Pages.app 2-0 Wed Sep 22 2010 RaoulScarazzinirasca@miamammausalinux.org Italian translation 3-0 Wed Feb 9 2011 AndrewBeekhofandrew@beekhof.net Updated for Fedora 13 4-0 Wed Oct 5 2011 AndrewBeekhofandrew@beekhof.net Update the GFS2 section to use CMAN 5-0 Fri Feb 10 2012 AndrewBeekhofandrew@beekhof.net Generate docbook content from asciidoc sources 6-0 Tues July 3 2012 AndrewBeekhofandrew@beekhof.net Updated for Fedora 17 7-0 Fri Sept 14 2012 DavidVosseldvossel@redhat.com Updated for pcs 8-0 Mon Jan 05 2015 KenGaillotkgaillot@redhat.com Updated for Fedora 21 + + 8-1 + Thu Jan 08 2015 + KenGaillotkgaillot@redhat.com + Minor corrections, plus use include file for intro + diff --git a/doc/Pacemaker_Explained/en-US/Ap-Install.txt b/doc/Pacemaker_Explained/en-US/Ap-Install.txt index 7eb587bc0e..601a999b94 100644 --- a/doc/Pacemaker_Explained/en-US/Ap-Install.txt +++ b/doc/Pacemaker_Explained/en-US/Ap-Install.txt @@ -1,119 +1,119 @@ [appendix] [[ap-install]] == Installation == [WARNING] The following text may no longer be accurate in some places. === Choosing a Cluster Stack === indexterm:[Cluster,Choosing Between Heartbeat and Corosync] indexterm:[Cluster Stack,Corosync] indexterm:[Corosync] indexterm:[Cluster Stack,Heartbeat] indexterm:[Heartbeat] Ultimately the choice of cluster stack is a personal decision that must be made in the context of you or your company's needs and strategic direction. Pacemaker currently functions equally well with both stacks. Here are some factors that may influence the decision: * SUSE/Novell, Red Hat and Oracle are all putting their collective weight behind the Corosync cluster stack. * Using Corosync gives your applications access to the following additional cluster services ** distributed locking service ** extended virtual synchronization service ** cluster closed process group service * It is likely that Pacemaker, at some point in the future, will make use of some of these additional services not provided by Heartbeat === Enabling Pacemaker === ==== For Corosync ==== The Corosync configuration is normally located in '/etc/corosync/corosync.conf' and an example for a machine with an address of +1.2.3.4+ in a cluster communicating on port 1234 (without peer authentication and message encryption) is shown below. .An example Corosync configuration file [source,XML] ------- totem { version: 2 secauth: off threads: 0 interface { ringnumber: 0 bindnetaddr: 1.2.3.4 mcastaddr: 239.255.1.1 mcastport: 1234 } } logging { fileline: off to_syslog: yes syslog_facility: daemon } amf { mode: disabled } ------- The logging should be mostly obvious and the amf section refers to the Availability Management Framework and is not covered in this document. The interesting part of the configuration is the totem section. This is where we define how the node can communicate with the rest of the cluster and what protocol version and options (including encryption footnote:[ Please consult the Corosync website (http://www.corosync.org/) and documentation for details on enabling encryption and peer authentication for the cluster. ] ) it should use. Beginners are encouraged to use the values shown and modify the interface section based on their network. It is also possible to configure Corosync for an IPv6 based environment. Simply configure +bindnetaddr+ and +mcastaddr+ with their IPv6 equivalents, eg. .Example options for an IPv6 environment -[source,Bash] ------- bindnetaddr: fec0::1:a800:4ff:fe00:20 mcastaddr: ff05::1 ------- To tell Corosync to use the Pacemaker cluster manager, add the following fragment to a functional Corosync configuration and restart the cluster. .Configuration fragment for enabling Pacemaker under Corosync [source,XML] ------- aisexec { user: root group: root } service { name: pacemaker ver: 0 } ------- The cluster needs to be run as root so that its child processes (the +lrmd+ in particular) have sufficient privileges to perform the actions requested of it. After all, a cluster manager that can't add an IP address or start apache is of little use. The second directive is the one that actually instructs the cluster to run Pacemaker. ==== For Heartbeat ==== Add the following to a functional _ha.cf_ configuration file and restart Heartbeat: .Configuration fragment for enabling Pacemaker under Heartbeat -[source,Bash] +---- crm respawn +---- diff --git a/doc/Pacemaker_Explained/en-US/Ap-LSB.txt b/doc/Pacemaker_Explained/en-US/Ap-LSB.txt index 62d1d16c5e..8fa80f2b05 100644 --- a/doc/Pacemaker_Explained/en-US/Ap-LSB.txt +++ b/doc/Pacemaker_Explained/en-US/Ap-LSB.txt @@ -1,76 +1,82 @@ [appendix] [[ap-lsb]] == init-Script LSB Compliance == The relevant part of http://refspecs.freestandards.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html[LSB spec] includes a description of all the return codes listed here. Assuming +some_service+ is configured correctly and currently not active, the following sequence will help you determine if it is LSB compatible: . Start (stopped): + -[source,C] +---- # /etc/init.d/some_service start ; echo "result: $?" +---- + .. Did the service start? .. Did the command print result: 0 (in addition to the regular output)? + . Status (running): + -[source,C] +---- # /etc/init.d/some_service status ; echo "result: $?" +---- + .. Did the script accept the command? .. Did the script indicate the service was running? .. Did the command print result: 0 (in addition to the regular output)? + . Start (running): + -[source,C] +---- # /etc/init.d/some_service start ; echo "result: $?" +---- + .. Is the service still running? .. Did the command print result: 0 (in addition to the regular output)? + . Stop (running): + -[source,C] +---- # /etc/init.d/some_service stop ; echo "result: $?" +---- + .. Was the service stopped? .. Did the command print result: 0 (in addition to the regular output)? + . Status (stopped): + -[source,C] +---- # /etc/init.d/some_service status ; echo "result: $?" +---- + .. Did the script accept the command? .. Did the script indicate the service was not running? .. Did the command print result: 3 (in addition to the regular output)? + . Stop (stopped): + -[source,C] +---- # /etc/init.d/some_service stop ; echo "result: $?" +---- + .. Is the service still stopped? .. Did the command print result: 0 (in addition to the regular output)? + . Status (failed): + This step is not readily testable and relies on manual inspection of the script. + The script can use one of the error codes (other than 3) listed in the LSB spec to indicate that it is active but failed. This tells the cluster that before moving the resource to another node, it needs to stop it on the existing one first. If the answer to any of the above questions is no, then the script is not LSB compliant. Your options are then to either fix the script or write an OCF agent based on the existing script. diff --git a/doc/Pacemaker_Explained/en-US/Ap-Upgrade-Config.txt b/doc/Pacemaker_Explained/en-US/Ap-Upgrade-Config.txt index db51b25840..d83618840c 100644 --- a/doc/Pacemaker_Explained/en-US/Ap-Upgrade-Config.txt +++ b/doc/Pacemaker_Explained/en-US/Ap-Upgrade-Config.txt @@ -1,138 +1,131 @@ [appendix] == Upgrading the Configuration from 0.6 == === Preparation === indexterm:[Upgrading the Configuration] indexterm:[Configuration,Upgrading] indexterm:[Download,DTD] indexterm:[DTD,Download] Download the latest http://hg.clusterlabs.org/pacemaker/stable-1.0/file-raw/tip/xml/crm.dtd[DTD] and ensure your configuration validates. === Perform the upgrade === ==== Upgrade the software ==== Refer to the appendix: <> ==== Upgrade the Configuration ==== As XML is not the friendliest of languages, it is common for cluster administrators to have scripted some of their activities. In such cases, it is likely that those scripts will not work with the new 1.0 syntax. In order to support such environments, it is actually possible to continue using the old 0.6 syntax. The downside is, however, that not all the new features will be available and there is a performance impact since the cluster must do a non-persistent configuration upgrade before each transition. So while using the old syntax is possible, it is not advisable to continue using it indefinitely. Even if you wish to continue using the old syntax, it is advisable to follow the upgrade procedure to ensure that the cluster is able to use your existing configuration (since it will perform much the same task internally). . Create a shadow copy to work with + -[source,C] ----- # crm_shadow --create upgrade06 ----- . Verify the configuration is valid indexterm:[Configuration,Verify]indexterm:[Verify,Configuration] + -[source,C] ----- # crm_verify --live-check ----- . Fix any errors or warnings . Perform the upgrade: + -[source,C] ----- # cibadmin --upgrade ----- . If this step fails, there are three main possibilities: .. The configuration was not valid to start with - go back to step 2 .. The transformation failed - report a bug or mailto:pacemaker@oss.clusterlabs.org?subject=Transformation%20failed%20during%20upgrade[email the project] .. The transformation was successful but produced an invalid result footnote:[ The most common reason is ID values being repeated or invalid. Pacemaker 1.0 is much stricter regarding this type of validation. ] + If the result of the transformation is invalid, you may see a number of errors from the validation library. If these are not helpful, visit http://clusterlabs.org/wiki/Validation_FAQ and/or try the procedure described below under <> + . Check the changes + -[source,C] ----- # crm_shadow --diff ----- + If at this point there is anything about the upgrade that you wish to fine-tune (for example, to change some of the automatic IDs) now is the time to do so. Since the shadow configuration is not in use by the cluster, it is safe to edit the file manually: + -[source,C] ----- # crm_shadow --edit ----- + This will open the configuration in your favorite editor (whichever is specified by the standard +$EDITOR+ environment variable) + . Preview how the cluster will react + Test what the cluster will do when you upload the new configuration + -[source,C] ------ # crm_simulate --live-check --save-dotfile upgrade06.dot -S # graphviz upgrade06.dot ------ + Verify that either no resource actions will occur or that you are happy with any that are scheduled. If the output contains actions you do not expect (possibly due to changes to the score calculations), you may need to make further manual changes. See <> for further details on how to interpret the output of `crm_simulate` + . Upload the changes + -[source,C] ----- # crm_shadow --commit upgrade06 --force ----- If this step fails, something really strange has occurred. You should report a bug. [[s-upgrade-config-manual]] ==== Manually Upgrading the Configuration ==== indexterm:[Configuration,Upgrade manually] It is also possible to perform the configuration upgrade steps manually. To do this Locate the 'upgrade06.xsl' conversion script or download the latest version from https://github.com/ClusterLabs/pacemaker/tree/master/xml/upgrade06.xsl[Git] . Convert the XML blob: indexterm:[XML,Convert] + -[source,C] ----- # xsltproc /path/to/upgrade06.xsl config06.xml > config10.xml ----- + . Locate the 'pacemaker.rng' script. . Check the XML validity: indexterm:[Validate Configuration]indexterm:[Configuration,Validate XML] + -[source,C] +---- # xmllint --relaxng /path/to/pacemaker.rng config10.xml +---- The advantage of this method is that it can be performed without the cluster running and any validation errors should be more informative (despite being generated by the same library!) since they include line numbers. diff --git a/doc/Pacemaker_Explained/en-US/Ap-Upgrade.txt b/doc/Pacemaker_Explained/en-US/Ap-Upgrade.txt index dc14d71a1b..dbf762262e 100644 --- a/doc/Pacemaker_Explained/en-US/Ap-Upgrade.txt +++ b/doc/Pacemaker_Explained/en-US/Ap-Upgrade.txt @@ -1,216 +1,220 @@ [appendix] [[ap-upgrade]] == Upgrading Cluster Software === Version Compatibility === When releasing newer versions we take care to make sure we are backwards compatible with older versions. While you will always be able to upgrade from version x to x+1, in order to continue to produce high quality software it may occasionally be necessary to drop compatibility with older versions. There will always be an upgrade path from any series-2 release to any other series-2 release. There are three approaches to upgrading your cluster software: * Complete Cluster Shutdown * Rolling (node by node) * Disconnect and Reattach Each method has advantages and disadvantages, some of which are listed in the table below, and you should chose the one most appropriate to your needs. .Summary of Upgrade Methodologies [width="95%",cols="6*",options="header",align="center"] |========================================================= |Type |Available between all software versions |Service Outage During Upgrade |Service Recovery During Upgrade |Exercises Failover Logic/Configuration |Allows change of cluster stack type indexterm:[Cluster,Switching between Stacks] indexterm:[Changing Cluster Stack] footnote:[ For example, switching from Heartbeat to Corosync. Consult the Heartbeat or Corosync documentation to see if upgrading them to a newer version is also supported. ] |Shutdown indexterm:[Upgrade,Shutdown] indexterm:[Shutdown Upgrade] |yes |always |N/A |no |yes |Rolling indexterm:[Upgrade,Rolling] indexterm:[Rolling Upgrade] |no |always |yes |yes |no |Reattach indexterm:[Upgrade,Reattach] indexterm:[Reattach Upgrade] |yes |only due to failure |no |no |yes |========================================================= === Complete Cluster Shutdown === In this scenario one shuts down all cluster nodes and resources and upgrades all the nodes before restarting the cluster. ==== Procedure ==== . On each node: .. Shutdown the cluster stack (Heartbeat or Corosync) .. Upgrade the Pacemaker software. This may also include upgrading the cluster stack and/or the underlying operating system. .. Check the configuration manually or with the `crm_verify` tool if available. . On each node: .. Start the cluster stack. This can be either Corosync or Heartbeat and does not need to be the same as the previous cluster stack. === Rolling (node by node) === In this scenario each node is removed from the cluster, upgraded and then brought back online until all nodes are running the newest version. [IMPORTANT] =========== This method is currently broken between Pacemaker 0.6.x and 1.0.x. Measures have been put into place to ensure rolling upgrades always work for versions after 1.0.0. Please try one of the other upgrade strategies. Detach/Reattach is a particularly good option for most people. =========== ==== Procedure ==== On each node: . Shutdown the cluster stack (Heartbeat or Corosync) . Upgrade the Pacemaker software. This may also include upgrading the cluster stack and/or the underlying operating system. .. On the first node, check the configuration manually or with the `crm_verify` tool if available. .. Start the cluster stack. + This must be the same type of cluster stack (Corosync or Heartbeat) that the rest of the cluster is using. Upgrading Corosync/Heartbeat may also be possible, please consult the documentation for those projects to see if the two versions will be compatible. + .. Repeat for each node in the cluster. ==== Version Compatibility ==== .Version Compatibility Table [width="95%",cols="2*",options="header",align="center"] |========================================================= |Version being Installed |Oldest Compatible Version |Pacemaker 1.0.x |Pacemaker 1.0.0 |Pacemaker 0.7.x |Pacemaker 0.6 or Heartbeat 2.1.3 |Pacemaker 0.6.x |Heartbeat 2.0.8 |Heartbeat 2.1.3 (or less) |Heartbeat 2.0.4 |Heartbeat 2.0.4 (or less) |Heartbeat 2.0.0 |Heartbeat 2.0.0 |None. Use an alternate upgrade strategy. |========================================================= ==== Crossing Compatibility Boundaries ==== Rolling upgrades that cross compatibility boundaries must be preformed in multiple steps. For example, to perform a rolling update from Heartbeat 2.0.1 to Pacemaker 0.6.6 one must: . Perform a rolling upgrade from Heartbeat 2.0.1 to Heartbeat 2.0.4 . Perform a rolling upgrade from Heartbeat 2.0.4 to Heartbeat 2.1.3 . Perform a rolling upgrade from Heartbeat 2.1.3 to Pacemaker 0.6.6 === Disconnect and Reattach === A variant of a complete cluster shutdown, but the resources are left active and get re-detected when the cluster is restarted. ==== Procedure ==== . Tell the cluster to stop managing services. + This is required to allow the services to remain active after the cluster shuts down. + -[source,C] +---- # crm_attribute -t crm_config -n is-managed-default -v false +---- + . For any resource that has a value for +is-managed+, make sure it is set to +false+ (so that the cluster will not stop it) + -[source,C] +---- # crm_resource -t primitive -r $rsc_id -p is-managed -v false +---- + . On each node: .. Shutdown the cluster stack (Heartbeat or Corosync) .. Upgrade the cluster stack program - This may also include upgrading the underlying operating system. . Check the configuration manually or with the `crm_verify` tool if available. . On each node: .. Start the cluster stack. + This can be either Corosync or Heartbeat and does not need to be the same as the previous cluster stack. + . Verify that the cluster re-detected all resources correctly. . Allow the cluster to resume managing resources again: + -[source,C] +---- # crm_attribute -t crm_config -n is-managed-default -v true +---- + . For any resource that has a value for +is-managed+ reset it to +true+ (so the cluster can recover the service if it fails) if desired: + -[source,C] +---- # crm_resource -t primitive -r $rsc_id -p is-managed -v true +---- ==== Notes ==== [IMPORTANT] =========== Always check your existing configuration is still compatible with the version you are installing before starting the cluster. =========== [NOTE] The oldest version of the CRM to support this upgrade type was in Heartbeat 2.0.4 diff --git a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt index ab9a089617..e3dde0b1aa 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt @@ -1,673 +1,682 @@ = Advanced Configuration = [[s-remote-connection]] == Connecting from a Remote Machine == indexterm:[Cluster,Remote connection] indexterm:[Cluster,Remote administration] Provided Pacemaker is installed on a machine, it is possible to connect to the cluster even if the machine itself is not in the same cluster. To do this, one simply sets up a number of environment variables and runs the same commands as when working on a cluster node. .Environment Variables Used to Connect to Remote Instances of the CIB [width="95%",cols="1m,2<",options="header",align="center"] |========================================================= |Environment Variable |Description |CIB_user |The user to connect as. Needs to be part of the +hacluster+ group on the target host. Defaults to _$USER_. indexterm:[Environment Variable,CIB_user] |CIB_passwd |The user's password. Read from the command line if unset. indexterm:[Environment Variable,CIB_passwd] |CIB_server |The host to contact. Defaults to _localhost_. indexterm:[Environment Variable,CIB_server] |CIB_port |The port on which to contact the server; required. indexterm:[Environment Variable,CIB_port] |CIB_encrypted |Encrypt network traffic; defaults to _true_. indexterm:[Environment Variable,CIB_encrypted] |========================================================= So, if +c001n01+ is an active cluster node and is listening on +1234+ for connections, and +someguy+ is a member of the +hacluster+ group, then the following would prompt for +someguy+'s password and return the cluster's current configuration: -[source,C] +---- # export CIB_port=1234; export CIB_server=c001n01; export CIB_user=someguy; # cibadmin -Q +---- For security reasons, the cluster does not listen for remote connections by default. If you wish to allow remote access, you need to set the +remote-tls-port+ (encrypted) or +remote-clear-port+ (unencrypted) top-level options (ie., those kept in the cib tag, like +num_updates+ and +epoch+). .Extra top-level CIB options for remote access [width="95%",cols="1m,2<",options="header",align="center"] |========================================================= |Field |Description |remote-tls-port |Listen for encrypted remote connections on this port. Default: _none_ indexterm:[remote-tls-port,Remote Connection Option] indexterm:[Remote Connection,Option,remote-tls-port] |remote-clear-port |Listen for plaintext remote connections on this port. Default: _none_ indexterm:[remote-clear-port,Remote Connection Option] indexterm:[Remote Connection,Option,remote-clear-port] |========================================================= [[s-recurring-start]] == Specifying When Recurring Actions are Performed == By default, recurring actions are scheduled relative to when the resource started. So if your resource was last started at 14:32 and you have a backup set to be performed every 24 hours, then the backup will always run at in the middle of the business day - hardly desirable. To specify a date/time that the operation should be relative to, set the operation's +interval-origin+. The cluster uses this point to calculate the correct +start-delay+ such that the operation will occur at _origin + (interval * N)_. So, if the operation's interval is 24h, it's interval-origin is set to +02:00+ and it is currently +14:32+, then the cluster would initiate the operation with a start delay of 11 hours and 28 minutes. If the resource is moved to another node before 2am, then the operation is of course cancelled. The value specified for interval and +interval-origin+ can be any date/time conforming to the http://en.wikipedia.org/wiki/ISO_8601[ISO8601 standard]. By way of example, to specify an operation that would run on the first Monday of 2009 and every Monday after that you would add: .Specifying a Base for Recurring Action Intervals ===== [source,XML] ===== == Moving Resources == indexterm:[Moving,Resources] indexterm:[Resource,Moving] === Manual Intervention === There are primarily two occasions when you would want to move a resource from it's current location: when the whole node is under maintenance, and when a single resource needs to be moved. Since everything eventually comes down to a score, you could create constraints for every resource to prevent them from running on one node. While the configuration can seem convoluted at times, not even we would require this of administrators. Instead one can set a special node attribute which tells the cluster "don't let anything run here". There is even a helpful tool to help query and set it, called `crm_standby`. To check the standby status of the current machine, simply run: -[source,C] +---- # crm_standby --get-value +---- A value of +true+ indicates that the node is _NOT_ able to host any resources, while a value of +false+ says that it _CAN_. You can also check the status of other nodes in the cluster by specifying the `--node-uname` option: -[source,C] +---- # crm_standby --get-value --node-uname sles-2 +---- To change the current node's standby status, use `--attr-value` instead of `--get-value`. -[source,C] +---- # crm_standby --attr-value +---- Again, you can change another host's value by supplying a host name with `--node-uname`. When only one resource is required to move, we do this by creating location constraints. However, once again we provide a user friendly shortcut as part of the `crm_resource` command, which creates and modifies the extra constraints for you. If +Email+ was running on +sles-1+ and you wanted it moved to a specific location, the command would look something like: -[source,C] +---- # crm_resource -M -r Email -H sles-2 +---- Behind the scenes, the tool will create the following location constraint: [source,XML] It is important to note that subsequent invocations of `crm_resource -M` are not cumulative. So, if you ran these commands -[source,C] +---- # crm_resource -M -r Email -H sles-2 # crm_resource -M -r Email -H sles-3 +---- then it is as if you had never performed the first command. To allow the resource to move back again, use: -[source,C] +---- # crm_resource -U -r Email +---- Note the use of the word _allow_. The resource can move back to its original location but, depending on +resource-stickiness+, it might stay where it is. To be absolutely certain that it moves back to +sles-1+, move it there before issuing the call to `crm_resource -U`: -[source,C] +---- # crm_resource -M -r Email -H sles-1 # crm_resource -U -r Email +---- Alternatively, if you only care that the resource should be moved from its current location, try -[source,C] +---- # crm_resource -M -r Email` +---- Which will instead create a negative constraint, like [source,XML] This will achieve the desired effect, but will also have long-term consequences. As the tool will warn you, the creation of a +-INFINITY+ constraint will prevent the resource from running on that node until `crm_resource -U` is used. This includes the situation where every other cluster node is no longer available! In some cases, such as when +resource-stickiness+ is set to +INFINITY+, it is possible that you will end up with the problem described in <>. The tool can detect some of these cases and deals with them by also creating both a positive and negative constraint. Eg. +Email+ prefers +sles-1+ with a score of +-INFINITY+ +Email+ prefers +sles-2+ with a score of +INFINITY+ which has the same long-term consequences as discussed earlier. [[s-failure-migration]] === Moving Resources Due to Failure === New in 1.0 is the concept of a migration threshold. footnote:[ The naming of this option was perhaps unfortunate as it is easily confused with true migration, the process of moving a resource from one node to another without stopping it. Xen virtual guests are the most common example of resources that can be migrated in this manner. ] Simply define +migration-threshold=N+ for a resource and it will migrate to a new node after N failures. There is no threshold defined by default. To determine the resource's current failure status and limits, use `crm_mon --failcounts`. By default, once the threshold has been reached, this node will no longer be allowed to run the failed resource until the administrator manually resets the resource's failcount using `crm_failcount` (after hopefully first fixing the failure's cause). However it is possible to expire them by setting the resource's +failure-timeout+ option. So a setting of +migration-threshold=2+ and +failure-timeout=60s+ would cause the resource to move to a new node after 2 failures, and allow it to move back (depending on the stickiness and constraint scores) after one minute. There are two exceptions to the migration threshold concept; they occur when a resource either fails to start or fails to stop. Start failures cause the failcount to be set to +INFINITY+ and thus always cause the resource to move immediately. Stop failures are slightly different and crucial. If a resource fails to stop and STONITH is enabled, then the cluster will fence the node in order to be able to start the resource elsewhere. If STONITH is not enabled, then the cluster has no way to continue and will not try to start the resource elsewhere, but will try to stop it again after the failure timeout. [IMPORTANT] Please read <> before enabling this option. === Moving Resources Due to Connectivity Changes === Setting up the cluster to move resources when external connectivity is lost is a two-step process. ==== Tell Pacemaker to monitor connectivity ==== To do this, you need to add a +ping+ resource to the cluster. The +ping+ resource uses the system utility of the same name to a test if list of machines (specified by DNS hostname or IPv4/IPv6 address) are reachable and uses the results to maintain a node attribute normally called +pingd+. footnote:[ The attribute name is customizable; that allows multiple ping groups to be defined. ] [NOTE] Older versions of Heartbeat required users to add ping nodes to _ha.cf_ - this is no longer required. [IMPORTANT] =========== Older versions of Pacemaker used a custom binary called 'pingd' for this functionality; this is now deprecated in favor of 'ping'. If your version of Pacemaker does not contain the ping agent, you can download the latest version from https://github.com/ClusterLabs/pacemaker/tree/master/extra/resources/ping =========== Normally the resource will run on all cluster nodes, which means that you'll need to create a clone. A template for this can be found below along with a description of the most interesting parameters. .Common Options for a 'ping' Resource [width="95%",cols="1m,4<",options="header",align="center"] |========================================================= |Field |Description |dampen |The time to wait (dampening) for further changes to occur. Use this to prevent a resource from bouncing around the cluster when cluster nodes notice the loss of connectivity at slightly different times. indexterm:[dampen,Ping Resource Option] indexterm:[Ping Resource,Option,dampen] |multiplier |The number of connected ping nodes gets multiplied by this value to get a score. Useful when there are multiple ping nodes configured. indexterm:[multiplier,Ping Resource Option] indexterm:[Ping Resource,Option,multiplier] |host_list |The machines to contact in order to determine the current connectivity status. Allowed values include resolvable DNS host names, IPv4 and IPv6 addresses. indexterm:[host_list,Ping Resource Option] indexterm:[Ping Resource,Option,host_list] |========================================================= .An example ping cluster resource that checks node connectivity once every minute ===== [source,XML] ------------ ------------ ===== [IMPORTANT] =========== You're only half done. The next section deals with telling Pacemaker how to deal with the connectivity status that +ocf:pacemaker:ping+ is recording. =========== ==== Tell Pacemaker how to interpret the connectivity data ==== [NOTE] ====== Before reading the following, please make sure you have read and understood <> above. ====== There are a number of ways to use the connectivity data provided by Heartbeat. The most common setup is for people to have a single ping node, to prevent the cluster from running a resource on any unconnected node. //// TODO: is the idea that only nodes that can reach eg. the router should have active resources? //// .Don't run on unconnected nodes ===== [source,XML] ------- ------- ===== A more complex setup is to have a number of ping nodes configured. You can require the cluster to only run resources on nodes that can connect to all (or a minimum subset) of them. .Run only on nodes connected to three or more ping nodes; this assumes +multiplier+ is set to 1000: ===== [source,XML] ------- ------- ===== Instead you can tell the cluster only to _prefer_ nodes with the best connectivity. Just be sure to set +multiplier+ to a value higher than that of +resource-stickiness+ (and don't set either of them to +INFINITY+). .Prefer the node with the most connected ping nodes ===== [source,XML] ------- ------- ===== It is perhaps easier to think of this in terms of the simple constraints that the cluster translates it into. For example, if +sles-1+ is connected to all 5 ping nodes but +sles-2+ is only connected to 2, then it would be as if you instead had the following constraints in your configuration: .How the cluster translates the pingd constraint ===== [source,XML] ------- ------- ===== The advantage is that you don't have to manually update any constraints whenever your network connectivity changes. You can also combine the concepts above into something even more complex. The example below shows how you can prefer the node with the most connected ping nodes provided they have connectivity to at least three (again assuming that +multiplier+ is set to 1000). .A more complex example of choosing a location based on connectivity ===== [source,XML] ------- ------- ===== === Resource Migration === Some resources, such as Xen virtual guests, are able to move to another location without loss of state. We call this resource migration; this is different from the normal practice of stopping the resource on the first machine and starting it elsewhere. Not all resources are able to migrate, see the Migration Checklist below, and those that can, won't do so in all situations. Conceptually there are two requirements from which the other prerequisites follow: * the resource must be active and healthy at the old location * everything required for the resource to run must be available on both the old and new locations The cluster is able to accommodate both push and pull migration models by requiring the resource agent to support two new actions: +migrate_to+ (performed on the current location) and +migrate_from+ (performed on the destination). In push migration, the process on the current location transfers the resource to the new location where is it later activated. In this scenario, most of the work would be done in the +migrate_to+ action and, if anything, the activation would occur during +migrate_from+. Conversely for pull, the +migrate_to+ action is practically empty and +migrate_from+ does most of the work, extracting the relevant resource state from the old location and activating it. There is no wrong or right way to implement migration for your service, as long as it works. ==== Migration Checklist ==== * The resource may not be a clone. * The resource must use an OCF style agent. * The resource must not be in a failed or degraded state. * The resource must not, directly or indirectly, depend on any primitive or group resources. * The resource must support two new actions: +migrate_to+ and +migrate_from+, and advertise them in its metadata. * The resource must have the +allow-migrate+ meta-attribute set to +true+ (which is not the default). //// TODO: how can a KVM with DRBD migrate? //// If the resource depends on a clone, and at the time the resource needs to be move, the clone has instances that are stopping and instances that are starting, then the resource will be moved in the traditional manner. The Policy Engine is not yet able to model this situation correctly and so takes the safe (yet less optimal) path. [[s-reusing-config-elements]] == Reusing Rules, Options and Sets of Operations == Sometimes a number of constraints need to use the same set of rules, and resources need to set the same options and parameters. To simplify this situation, you can refer to an existing object using an +id-ref+ instead of an id. So if for one resource you have [source,XML] ------ ------ Then instead of duplicating the rule for all your other resources, you can instead specify: .Referencing rules from other constraints ===== [source,XML] ------- ------- ===== [IMPORTANT] =========== The cluster will insist that the +rule+ exists somewhere. Attempting to add a reference to a non-existing rule will cause a validation failure, as will attempting to remove a +rule+ that is referenced elsewhere. =========== The same principle applies for +meta_attributes+ and +instance_attributes+ as illustrated in the example below: .Referencing attributes, options, and operations from other resources ===== [source,XML] ------- ------- ===== == Reloading Services After a Definition Change == The cluster automatically detects changes to the definition of services it manages. However, the normal response is to stop the service (using the old definition) and start it again (with the new definition). This works well, but some services are smarter and can be told to use a new set of options without restarting. To take advantage of this capability, your resource agent must: . Accept the +reload+ operation and perform any required actions. _The steps required here depend completely on your application!_ + .The DRBD Agent's Control logic for Supporting the +reload+ Operation ===== [source,Bash] ------- case $1 in start) drbd_start ;; stop) drbd_stop ;; reload) drbd_reload ;; monitor) drbd_monitor ;; *) drbd_usage exit $OCF_ERR_UNIMPLEMENTED ;; esac exit $? ------- ===== . Advertise the +reload+ operation in the +actions+ section of its metadata + .The DRBD Agent Advertising Support for the +reload+ Operation ===== [source,XML] ------- 1.1 Master/Slave OCF Resource Agent for DRBD ... ------- ===== . Advertise one or more parameters that can take effect using +reload+. + Any parameter with the +unique+ set to 0 is eligible to be used in this way. + .Parameter that can be changed using reload ===== [source,XML] ------- Full path to the drbd.conf file. Path to drbd.conf ------- ===== Once these requirements are satisfied, the cluster will automatically know to reload the resource (instead of restarting) when a non-unique fields changes. [NOTE] ====== The metadata is re-read when the resource is started. This may mean that the resource will be restarted the first time, even though you changed a parameter with +unique=0+ ====== [NOTE] ====== If both a unique and non-unique field are changed simultaneously, the resource will still be restarted. ====== diff --git a/doc/Pacemaker_Explained/en-US/Ch-Basics.txt b/doc/Pacemaker_Explained/en-US/Ch-Basics.txt index 6f73955e61..affa9e32d9 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Basics.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Basics.txt @@ -1,368 +1,370 @@ = Configuration Basics = == Configuration Layout == The cluster is written using XML notation and divided into two main sections: configuration and status. The status section contains the history of each resource on each node and based on this data, the cluster can construct the complete current state of the cluster. The authoritative source for the status section is the local resource manager (lrmd) process on each cluster node and the cluster will occasionally repopulate the entire section. For this reason it is never written to disk and administrators are advised against modifying it in any way. The configuration section contains the more traditional information like cluster options, lists of resources and indications of where they should be placed. The configuration section is the primary focus of this document. The configuration section itself is divided into four parts: * Configuration options (called +crm_config+) * Nodes * Resources * Resource relationships (called +constraints+) .An empty configuration ====== [source,XML] ------- ------- ====== == The Current State of the Cluster == Before one starts to configure a cluster, it is worth explaining how to view the finished product. For this purpose we have created the `crm_mon` utility that will display the current state of an active cluster. It can show the cluster status by node or by resource and can be used in either single-shot or dynamically-updating mode. There are also modes for displaying a list of the operations performed (grouped by node and resource) as well as information about failures. Using this tool, you can examine the state of the cluster for irregularities and see how it responds when you cause or simulate failures. Details on all the available options can be obtained using the `crm_mon --help` command. .Sample output from crm_mon ====== ------- ============ Last updated: Fri Nov 23 15:26:13 2007 Current DC: sles-3 (2298606a-6a8c-499a-9d25-76242f7006ec) 3 Nodes configured. 5 Resources configured. ============ Node: sles-1 (1186dc9a-324d-425a-966e-d757e693dc86): online 192.168.100.181 (heartbeat::ocf:IPaddr): Started sles-1 192.168.100.182 (heartbeat:IPaddr): Started sles-1 192.168.100.183 (heartbeat::ocf:IPaddr): Started sles-1 rsc_sles-1 (heartbeat::ocf:IPaddr): Started sles-1 child_DoFencing:2 (stonith:external/vmware): Started sles-1 Node: sles-2 (02fb99a8-e30e-482f-b3ad-0fb3ce27d088): standby Node: sles-3 (2298606a-6a8c-499a-9d25-76242f7006ec): online rsc_sles-2 (heartbeat::ocf:IPaddr): Started sles-3 rsc_sles-3 (heartbeat::ocf:IPaddr): Started sles-3 child_DoFencing:0 (stonith:external/vmware): Started sles-3 ------- ====== .Sample output from crm_mon -n ====== ------- ============ Last updated: Fri Nov 23 15:26:13 2007 Current DC: sles-3 (2298606a-6a8c-499a-9d25-76242f7006ec) 3 Nodes configured. 5 Resources configured. ============ Node: sles-1 (1186dc9a-324d-425a-966e-d757e693dc86): online Node: sles-2 (02fb99a8-e30e-482f-b3ad-0fb3ce27d088): standby Node: sles-3 (2298606a-6a8c-499a-9d25-76242f7006ec): online Resource Group: group-1 192.168.100.181 (heartbeat::ocf:IPaddr): Started sles-1 192.168.100.182 (heartbeat:IPaddr): Started sles-1 192.168.100.183 (heartbeat::ocf:IPaddr): Started sles-1 rsc_sles-1 (heartbeat::ocf:IPaddr): Started sles-1 rsc_sles-2 (heartbeat::ocf:IPaddr): Started sles-3 rsc_sles-3 (heartbeat::ocf:IPaddr): Started sles-3 Clone Set: DoFencing child_DoFencing:0 (stonith:external/vmware): Started sles-3 child_DoFencing:1 (stonith:external/vmware): Stopped child_DoFencing:2 (stonith:external/vmware): Started sles-1 ------- ====== The DC (Designated Controller) node is where all the decisions are made and if the current DC fails a new one is elected from the remaining cluster nodes. The choice of DC is of no significance to an administrator beyond the fact that its logs will generally be more interesting. == How Should the Configuration be Updated? == There are three basic rules for updating the cluster configuration: * Rule 1 - Never edit the cib.xml file manually. Ever. I'm not making this up. * Rule 2 - Read Rule 1 again. * Rule 3 - The cluster will notice if you ignored rules 1 & 2 and refuse to use the configuration. Now that it is clear how NOT to update the configuration, we can begin to explain how you should. The most powerful tool for modifying the configuration is the +cibadmin+ command which talks to a running cluster. With +cibadmin+, the user can query, add, remove, update or replace any part of the configuration; all changes take effect immediately, so there is no need to perform a reload-like operation. The simplest way of using cibadmin is to use it to save the current configuration to a temporary file, edit that file with your favorite text or XML editor and then upload the revised configuration. .Safely using an editor to modify the cluster configuration ====== -[source,C] -------- # cibadmin --query > tmp.xml # vi tmp.xml # cibadmin --replace --xml-file tmp.xml -------- ====== Some of the better XML editors can make use of a Relax NG schema to help make sure any changes you make are valid. The schema describing the configuration can normally be found in '/usr/lib/heartbeat/pacemaker.rng' on most systems. If you only wanted to modify the resources section, you could instead do .Safely using an editor to modify a subsection of the cluster configuration ====== -[source,C] -------- # cibadmin --query --obj_type resources > tmp.xml # vi tmp.xml # cibadmin --replace --obj_type resources --xml-file tmp.xml -------- ====== to avoid modifying any other part of the configuration. == Quickly Deleting Part of the Configuration == Identify the object you wish to delete. Eg. run .Searching for STONITH related configuration items ====== -[source,C] +-------- # cibadmin -Q | grep stonith +-------- [source,XML] -------- -------- ====== Next identify the resource's tag name and id (in this case we'll choose +primitive+ and +child_DoFencing+). Then simply execute: -[source,C] +---- # cibadmin --delete --crm_xml '' +---- == Updating the Configuration Without Using XML == Some common tasks can also be performed with one of the higher level tools that avoid the need to read or edit XML. To enable stonith for example, one could run: -[source,C] +---- # crm_attribute --attr-name stonith-enabled --attr-value true +---- Or, to see if +somenode+ is allowed to run resources, there is: -[source,C] +---- # crm_standby --get-value --node-uname somenode +---- Or, to find the current location of +my-test-rsc+, one can use: -[source,C] +---- # crm_resource --locate --resource my-test-rsc +---- [[s-config-sandboxes]] == Making Configuration Changes in a Sandbox == Often it is desirable to preview the effects of a series of changes before updating the configuration atomically. For this purpose we have created `crm_shadow` which creates a "shadow" copy of the configuration and arranges for all the command line tools to use it. To begin, simply invoke `crm_shadow` and give it the name of a configuration to create footnote:[Shadow copies are identified with a name, making it possible to have more than one.] ; be sure to follow the simple on-screen instructions. WARNING: Read the above carefully, failure to do so could result in you destroying the cluster's active configuration! .Creating and displaying the active sandbox ====== -[source,Bash] --------- +---- # crm_shadow --create test Setting up shadow instance Type Ctrl-D to exit the crm_shadow shell shadow[test]: shadow[test] # crm_shadow --which test --------- +---- ====== From this point on, all cluster commands will automatically use the shadow copy instead of talking to the cluster's active configuration. Once you have finished experimenting, you can either commit the changes, or discard them as shown below. Again, be sure to follow the on-screen instructions carefully. For a full list of `crm_shadow` options and commands, invoke it with the --help option. .Using a sandbox to make multiple changes atomically ====== -[source,Bash] --------- +---- shadow[test] # crm_failcount -G -r rsc_c001n01 name=fail-count-rsc_c001n01 value=0 shadow[test] # crm_standby -v on -n c001n02 shadow[test] # crm_standby -G -n c001n02 name=c001n02 scope=nodes value=on shadow[test] # cibadmin --erase --force shadow[test] # cibadmin --query shadow[test] # crm_shadow --delete test --force Now type Ctrl-D to exit the crm_shadow shell shadow[test] # exit # crm_shadow --which No shadow instance provided # cibadmin -Q --------- +---- ====== Making changes in a sandbox and verifying the real configuration is untouched [[s-config-testing-changes]] == Testing Your Configuration Changes == We saw previously how to make a series of changes to a "shadow" copy of the configuration. Before loading the changes back into the cluster (eg. `crm_shadow --commit mytest --force`), it is often advisable to simulate the effect of the changes with +crm_simulate+, eg. -[source,C] +---- # crm_simulate --live-check -VVVVV --save-graph tmp.graph --save-dotfile tmp.dot +---- The tool uses the same library as the live cluster to show what it would have done given the supplied input. It's output, in addition to a significant amount of logging, is stored in two files +tmp.graph+ and +tmp.dot+, both are representations of the same thing -- the cluster's response to your changes. In the graph file is stored the complete transition, containing a list of all the actions, their parameters and their pre-requisites. Because the transition graph is not terribly easy to read, the tool also generates a Graphviz dot-file representing the same information. == Interpreting the Graphviz output == * Arrows indicate ordering dependencies * Dashed-arrows indicate dependencies that are not present in the transition graph * Actions with a dashed border of any color do not form part of the transition graph * Actions with a green border form part of the transition graph * Actions with a red border are ones the cluster would like to execute but cannot run * Actions with a blue border are ones the cluster does not feel need to be executed * Actions with orange text are pseudo/pretend actions that the cluster uses to simplify the graph * Actions with black text are sent to the LRM * Resource actions have text of the form pass:[rsc]_pass:[action]_pass:[interval] pass:[node] * Any action depending on an action with a red border will not be able to execute. * Loops are _really_ bad. Please report them to the development team. === Small Cluster Transition === image::images/Policy-Engine-small.png["An example transition graph as represented by Graphviz",width="16cm",height="6cm",align="center"] In the above example, it appears that a new node, +pcmk-2+, has come online and that the cluster is checking to make sure +rsc1+, +rsc2+ and +rsc3+ are not already running there (Indicated by the +*_monitor_0+ entries). Once it did that, and assuming the resources were not active there, it would have liked to stop +rsc1+ and +rsc2+ on +pcmk-1+ and move them to +pcmk-2+. However, there appears to be some problem and the cluster cannot or is not permitted to perform the stop actions which implies it also cannot perform the start actions. For some reason the cluster does not want to start +rsc3+ anywhere. For information on the options supported by `crm_simulate`, use the `--help` option. === Complex Cluster Transition === image::images/Policy-Engine-big.png["Another, slightly more complex, transition graph that you're not expected to be able to read",width="16cm",height="20cm",align="center"] == Do I Need to Update the Configuration on all Cluster Nodes? == No. Any changes are immediately synchronized to the other active members of the cluster. To reduce bandwidth, the cluster only broadcasts the incremental updates that result from your changes and uses MD5 checksums to ensure that each copy is completely consistent. diff --git a/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt b/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt index b4eaf49804..84d272b42c 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt @@ -1,665 +1,667 @@ = Resource Constraints = indexterm:[Resource,Constraints] == Scores == Scores of all kinds are integral to how the cluster works. Practically everything from moving a resource to deciding which resource to stop in a degraded cluster is achieved by manipulating scores in some way. Scores are calculated on a per-resource basis and any node with a negative score for a resource can't run that resource. After calculating the scores for a resource, the cluster then chooses the node with the highest one. === Infinity Math === +INFINITY+ is currently defined as 1,000,000 and addition/subtraction with it follows these three basic rules: * Any value + +INFINITY+ = +INFINITY+ * Any value - +INFINITY+ = -+INFINITY+ * +INFINITY+ - +INFINITY+ = -+INFINITY+ == Deciding Which Nodes a Resource Can Run On == indexterm:[Location Constraints] indexterm:[Resource,Constraints,Location] There are two alternative strategies for specifying which nodes a resources can run on. One way is to say that by default they can run anywhere and then create location constraints for nodes that are not allowed. The other option is to have nodes "opt-in"... to start with nothing able to run anywhere and selectively enable allowed nodes. === Options === .Options for Simple Location Constraints [width="95%",cols="2m,1,5<",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the constraint indexterm:[id,Location Constraints] indexterm:[Constraints,Location,id] |rsc | |A resource name indexterm:[rsc,Location Constraints] indexterm:[Constraints,Location,rsc] |node | |A node's name indexterm:[node,Location Constraints] indexterm:[Constraints,Location,node] |score | |Positive values indicate the resource should run on this node. Negative values indicate the resource should not run on this node. Values of \+/- +INFINITY+ change "should"/"should not" to "must"/"must not". indexterm:[score,Location Constraints] indexterm:[Constraints,Location,score] |resource-discovery |+always+ |Indicates whether or not Pacemaker should perform resource discovery on this node for the specified resource. Limiting resource discovery to a subset of nodes the resource is physically capable of running on can significantly boost performance when a large set of nodes are preset. When pacemaker_remote is in use to expand the node count into the 100s of nodes range, this option should be considered. * 'always' - Always perform resource discovery for the specified resource on this node. * 'never' - Never perform resource discovery for the specified resource on this node. This option should generally be used with a -INFINITY score. Although that is not strictly required. * 'exclusive' - Only perform resource discovery for the specified resource on this node. Multiple location constraints using 'exclusive' discovery for the same resource across different nodes creates a subset of nodes resource-discovery is exclusive to. If a resource is marked for 'exclusive' discovery on one or more nodes, that resource is only allowed to be placed within that subset of nodes. indexterm:[Resource Discovery,Location Constraints] indexterm:[Constraints,Location,Resource Discovery] |========================================================= === Asymmetrical "Opt-In" Clusters === indexterm:[Asymmetrical Opt-In Clusters] indexterm:[Cluster Type,Asymmetrical Opt-In] To create an opt-in cluster, start by preventing resources from running anywhere by default: -[source,C] +---- # crm_attribute --attr-name symmetric-cluster --attr-value false +---- Then start enabling nodes. The following fragment says that the web server prefers +sles-1+, the database prefers +sles-2+ and both can fail over to +sles-3+ if their most preferred node fails. .Example set of opt-in location constraints ====== [source,XML] ------- ------- ====== === Symmetrical "Opt-Out" Clusters === indexterm:[Symmetrical Opt-Out Clusters] indexterm:[Cluster Type,Symmetrical Opt-Out] To create an opt-out cluster, start by allowing resources to run anywhere by default: -[source,C] +---- # crm_attribute --attr-name symmetric-cluster --attr-value true +---- Then start disabling nodes. The following fragment is the equivalent of the above opt-in configuration. .Example set of opt-out location constraints ====== [source,XML] ------- ------- ====== Whether you should choose opt-in or opt-out depends both on your personal preference and the make-up of your cluster. If most of your resources can run on most of the nodes, then an opt-out arrangement is likely to result in a simpler configuration. On the other-hand, if most resources can only run on a small subset of nodes an opt-in configuration might be simpler. [[node-score-equal]] === What if Two Nodes Have the Same Score === If two nodes have the same score, then the cluster will choose one. This choice may seem random and may not be what was intended, however the cluster was not given enough information to know any better. .Example of two resources that prefer two nodes equally ====== [source,XML] ------- ------- ====== In the example above, assuming no other constraints and an inactive cluster, Webserver would probably be placed on sles-1 and Database on sles-2. It would likely have placed Webserver based on the node's uname and Database based on the desire to spread the resource load evenly across the cluster. However other factors can also be involved in more complex configurations. [[s-resource-ordering]] == Specifying in which Order Resources Should Start/Stop == indexterm:[Resource,Constraints,Ordering] indexterm:[Resource,Start Order] indexterm:[Ordering Constraints] The way to specify the order in which resources should start is by creating +rsc_order+ constraints. .Properties of an Ordering Constraint [width="95%",cols="2m,5<",options="header",align="center"] |========================================================= |Field |Description |id |A unique name for the constraint indexterm:[id,Ordering Constraints] indexterm:[Constraints,Ordering,id] |first |The name of a resource that must be started before the +then+ resource is allowed to. indexterm:[first,Ordering Constraints] indexterm:[Constraints,Ordering,first] |then |The name of a resource. This resource will start after the +first+ resource. indexterm:[then,Ordering Constraints] indexterm:[Constraints,Ordering,then] |kind |How to enforce the constraint. ('Since 1.1.2') * Optional - Just a suggestion. Only applies if both resources are starting/stopping. * Mandatory - Always. If 'first' is stopping or cannot be started, 'then' must be stopped. * Serialize - Ensure that no two stop/start actions occur concurrently for a set of resources. indexterm:[kind,Ordering Constraints] indexterm:[Constraints,Ordering,kind] |symmetrical |If true, which is the default, stop the resources in the reverse order. Default value: _true_ indexterm:[symmetrical,Ordering Constraints] indexterm:[Ordering Constraints,symmetrical] |========================================================= === Mandatory Ordering === When the +then+ resource cannot run without the +first+ resource being active, one should use mandatory constraints. To specify a constraint is mandatory, use scores greater than zero. This will ensure that the then resource will react when the first resource changes state. * If the +first+ resource was running and is stopped, the +then+ resource will also be stopped (if it is running). * If the +first+ resource was not running and cannot be started, the +then+ resource will be stopped (if it is running). * If the +first+ resource is (re)started while the +then+ resource is running, the +then+ resource will be stopped and restarted. === Advisory Ordering === On the other hand, when +score="0"+ is specified for a constraint, the constraint is considered optional and only has an effect when both resources are stopping and/or starting. Any change in state by the +first+ resource will have no effect on the +then+ resource. .Example of an optional and mandatory ordering constraint ====== [source,XML] ------- ------- ====== Some additional information on ordering constraints can be found in the document http://clusterlabs.org/doc/Ordering_Explained.pdf[Ordering Explained]. [[s-resource-colocation]] == Placing Resources Relative to other Resources == indexterm:[Resource,Constraints,Colocation] indexterm:[Resource,Location Relative to other Resources] When the location of one resource depends on the location of another one, we call this colocation. There is an important side-effect of creating a colocation constraint between two resources: it affects the order in which resources are assigned to a node. If you think about it, it's somewhat obvious. You can't place A relative to B unless you know where B is. footnote:[ While the human brain is sophisticated enough to read the constraint in any order and choose the correct one depending on the situation, the cluster is not quite so smart. Yet. ] So when you are creating colocation constraints, it is important to consider whether you should colocate A with B or B with A. Another thing to keep in mind is that, assuming A is collocated with B, the cluster will also take into account A's preferences when deciding which node to choose for B. For a detailed look at exactly how this occurs, see the http://www.clusterlabs.org/mediawiki/images/6/61/Colocation_Explained.pdf[Colocation Explained] document. === Options === .Properties of a Collocation Constraint [width="95%",cols="2m,5<",options="header",align="center"] |========================================================= |Field |Description |id |A unique name for the constraint. indexterm:[id,Colocation Constraints] indexterm:[Constraints,Colocation,id] |rsc |The colocation source. If the constraint cannot be satisfied, the cluster may decide not to allow the resource to run at all. indexterm:[rsc,Colocation Constraints] indexterm:[Constraints,Colocation,rsc] |with-rsc |The colocation target. The cluster will decide where to put this resource first and then decide where to put the resource in the +rsc+ field. indexterm:[with-rsc,Colocation Constraints] indexterm:[Constraints,Colocation,with-rsc] |score |Positive values indicate the resource should run on the same node. Negative values indicate the resources should not run on the same node. Values of \+/- +INFINITY+ change "should" to "must". indexterm:[score,Colocation Constraints] indexterm:[Constraints,Colocation,score] |========================================================= === Mandatory Placement === Mandatory placement occurs any time the constraint's score is ++INFINITY+ or +-INFINITY+. In such cases, if the constraint can't be satisfied, then the +rsc+ resource is not permitted to run. For +score=INFINITY+, this includes cases where the +with-rsc+ resource is not active. If you need +resource1+ to always run on the same machine as +resource2+, you would add the following constraint: .An example colocation constraint [source,XML] Remember, because +INFINITY+ was used, if +resource2+ can't run on any of the cluster nodes (for whatever reason) then +resource1+ will not be allowed to run. Alternatively, you may want the opposite... that +resource1+ cannot run on the same machine as +resource2+. In this case use +score="-INFINITY"+ .An example anti-colocation constraint [source,XML] Again, by specifying +-INFINTY+, the constraint is binding. So if the only place left to run is where +resource2+ already is, then +resource1+ may not run anywhere. === Advisory Placement === If mandatory placement is about "must" and "must not", then advisory placement is the "I'd prefer if" alternative. For constraints with scores greater than +-INFINITY+ and less than +INFINITY+, the cluster will try and accommodate your wishes but may ignore them if the alternative is to stop some of the cluster resources. Like in life, where if enough people prefer something it effectively becomes mandatory, advisory colocation constraints can combine with other elements of the configuration to behave as if they were mandatory. .An example advisory-only colocation constraint [source,XML] [[s-resource-sets-ordering]] == Ordering Sets of Resources == A common situation is for an administrator to create a chain of ordered resources, such as: .A chain of ordered resources ====== [source,XML] ------- ------- ====== .Visual representation of the four resources' start order for the above constraints image::images/resource-set.png["Ordered set",width="16cm",height="2.5cm",align="center"] === Ordered Set === To simplify this situation, there is an alternate format for ordering constraints: .A chain of ordered resources expressed as a set ====== [source,XML] ------- ------- ====== [WARNING] ========= Always pay attention to how your tools expose this functionality. In some tools +create set A B+ is *NOT* equivalent to +create A then B+. ========= While the set-based format is not less verbose, it is significantly easier to get right and maintain. It can also be expanded to allow ordered sets of (un)ordered resources. In the example below, +rscA+ and +rscB+ can both start in parallel, as can +rscC+ and +rscD+, however +rscC+ and +rscD+ can only start once _both_ +rscA+ _and_ +rscB+ are active. .Ordered sets of unordered resources ====== [source,XML] ------- ------- ====== .Visual representation of the start order for two ordered sets of unordered resources image::images/two-sets.png["Two ordered sets",width="13cm",height="7.5cm",align="center"] Of course either set -- or both sets -- of resources can also be internally ordered (by setting +sequential="true"+) and there is no limit to the number of sets that can be specified. .Advanced use of set ordering - Three ordered sets, two of which are internally unordered ====== [source,XML] ------- ------- ====== .Visual representation of the start order for the three sets defined above image::images/three-sets.png["Three ordered sets",width="16cm",height="7.5cm",align="center"] === Resource Set OR Logic === The unordered set logic discussed so far has all been "AND" logic. To illustrate this take the 3 resource set figure in the previous section. Those sets can be expressed, +(A and B) then (C) then (D) then (E and F)+ Say for example we want change the first set, (A and B), to use "OR" logic so the sets look like this, +(A or B) then (C) then (D) then (E and F)+. This functionality can be achieved through the use of the +require-all+ option. By default this option is 'require-all=true' which is why the "AND" logic is used by default. Changing +require-all=false+ means only one resource in the set needs to be started before continuing on to the next set. Note that the 'require-all=false' option only makes sense to use in conjunction with unordered sets, 'sequential=false'. Think of it like this, 'sequential=false' modifies the set to be an unordered set that uses "AND" logic by default, by adding 'require-all=false' the unordered set's "AND" logic is flipped to "OR" logic. .Resource Set "OR" logic. Three ordered sets, where the first set is internally unordered with "OR" logic. ====== [source,XML] ------- ------- ====== [[s-resource-sets-colocation]] == Collocating Sets of Resources == Another common situation is for an administrator to create a set of collocated resources. Previously this was possible either by defining a resource group (See <>) which could not always accurately express the design; or by defining each relationship as an individual constraint, causing a constraint explosion as the number of resources and combinations grew. .A chain of collocated resources ====== [source,XML] ------- ------- ====== To make things easier, we allow an alternate form of colocation constraints using +resource_sets+. Just like the expanded version, a resource that can't be active also prevents any resource that must be collocated with it from being active. For example, if +B+ was not able to run, then both +C+ (and by inference +D+) must also remain stopped. .The equivalent colocation chain expressed using +resource_sets+ ====== [source,XML] ------- ------- ====== [WARNING] ========= Always pay attention to how your tools expose this functionality. In some tools +create set A B+ is *NOT* equivalent to +create A with B+. ========= .A group resource with the equivalent colocation rules [source,XML] ------- ------- This notation can also be used in this context to tell the cluster that a set of resources must all be located with a common peer, but have no dependencies on each other. In this scenario, unlike the previous, +B would+ be allowed to remain active even if +A or+ +C+ (or both) were inactive. .Using colocation sets to specify a common peer. ====== [source,XML] ------- ------- ====== Of course there is no limit to the number and size of the sets used. The only thing that matters is that in order for any member of set N to be active, all the members of set N+1 must also be active (and naturally on the same node); and if a set has +sequential="true"+, then in order for member M to be active, member M+1 must also be active. You can even specify the role in which the members of a set must be in using the set's role attribute. .A colocation chain where the members of the middle set have no inter-dependencies and the last has master status. ====== [source,XML] ------- ------- ====== .Visual representation of a colocation chain where the members of the middle set have no inter-dependencies image::images/three-sets-complex.png["Colocation chain",width="16cm",height="9cm",align="center"] diff --git a/doc/Pacemaker_Explained/en-US/Ch-Intro.txt b/doc/Pacemaker_Explained/en-US/Ch-Intro.txt index fd05c81ad8..e61065115a 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Intro.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Intro.txt @@ -1,164 +1,23 @@ = Read-Me-First = == The Scope of this Document == The purpose of this document is to definitively explain the concepts used to configure Pacemaker. To achieve this, it will focus exclusively on the XML syntax used to configure the CIB. For those that are allergic to XML, there exist several unified shells and GUIs for Pacemaker. However these tools will not be covered at all in this document footnote:[I hope, however, that the concepts explained here make the functionality of these tools more easily understood.] , precisely because they hide the XML. Additionally, this document is NOT a step-by-step how-to guide for configuring a specific clustering scenario. -Although such guides exist, the purpose of this document is to provide -an understanding of the building blocks that can be used to construct -any type of Pacemaker cluster. +Although such guides exist, +footnote:[For example, see the http://www.clusterlabs.org/doc/[Clusters from Scratch] guide.] +the purpose of this document is to provide an understanding of the building +blocks that can be used to construct any type of Pacemaker cluster. -== What Is Pacemaker? == - -Pacemaker is a cluster resource manager. - -It achieves maximum availability for your cluster services -(aka. resources) by detecting and recovering from node and -resource-level failures by making use of the messaging and membership -capabilities provided by your preferred cluster infrastructure (either -http://www.corosync.org/[Corosync] or -http://linux-ha.org/wiki/Heartbeat[Heartbeat]). - -Pacemaker's key features include: - - * Detection and recovery of node and service-level failures - * Storage agnostic, no requirement for shared storage - * Resource agnostic, anything that can be scripted can be clustered - * Supports STONITH for ensuring data integrity - * Supports large and small clusters - * Supports both quorate and resource driven clusters - * Supports practically any redundancy configuration - * Automatically replicated configuration that can be updated from any node - * Ability to specify cluster-wide service ordering, colocation and anti-colocation - * Support for advanced service types - ** Clones: for services which need to be active on multiple nodes - ** Multi-state: for services with multiple modes (eg. master/slave, primary/secondary) - * Unified, scriptable, cluster management tools. - -== Pacemaker Architecture == - -At the highest level, the cluster is made up of three pieces: - - * Non-cluster aware components. These pieces - include the resources themselves, scripts that start, stop and - monitor them, and also a local daemon that masks the differences - between the different standards these scripts implement. - - * Resource management. Pacemaker provides the brain that processes - and reacts to events regarding the cluster. These events include - nodes joining or leaving the cluster; resource events caused by - failures, maintenance, scheduled activities; and other - administrative actions. Pacemaker will compute the ideal state of - the cluster and plot a path to achieve it after any of these - events. This may include moving resources, stopping nodes and even - forcing them offline with remote power switches. - - * Low level infrastructure. Projects like Corosync, CMAN and - Heartbeat provide reliable messaging, membership and quorum - information about the cluster. - -When combined with Corosync, Pacemaker also supports popular open -source cluster filesystems. -footnote:[ -Even though Pacemaker also supports Heartbeat, the filesystems need to -use the stack for messaging and membership and Corosync seems to be -what they're standardizing on. - -Technically it would be possible for them to support Heartbeat as -well, however there seems little interest in this. -] - -Due to past standardization within the cluster filesystem community, -they make use of a common distributed lock manager which makes use of -Corosync for its messaging and membership capabilities (which nodes -are up/down) and Pacemaker for fencing services. - -.The Pacemaker Stack -image::images/pcmk-stack.png["The Pacemaker stack",width="10cm",height="7.5cm",align="center"] - -=== Internal Components === - -Pacemaker itself is composed of five key components: - - * CIB (aka. Cluster Information Base) - * CRMd (aka. Cluster Resource Management daemon) - * LRMd (aka. Local Resource Management daemon) - * PEngine (aka. PE or Policy Engine) - * STONITHd - -.Internal Components -image::images/pcmk-internals.png["Subsystems of a Pacemaker cluster",align="center",scaledwidth="65%"] - -The CIB uses XML to represent both the cluster's configuration and -current state of all resources in the cluster. The contents of the CIB -are automatically kept in sync across the entire cluster and are used -by the PEngine to compute the ideal state of the cluster and how it -should be achieved. - -This list of instructions is then fed to the DC (Designated -Controller). Pacemaker centralizes all cluster decision making by -electing one of the CRMd instances to act as a master. Should the -elected CRMd process, or the node it is on, fail... a new one is -quickly established. - -The DC carries out the PEngine's instructions in the required order by -passing them to either the LRMd (Local Resource Management daemon) or -CRMd peers on other nodes via the cluster messaging infrastructure -(which in turn passes them on to their LRMd process). - -The peer nodes all report the results of their operations back to the -DC and, based on the expected and actual results, will either execute -any actions that needed to wait for the previous one to complete, or -abort processing and ask the PEngine to recalculate the ideal cluster -state based on the unexpected results. - -In some cases, it may be necessary to power off nodes in order to -protect shared data or complete resource recovery. For this Pacemaker -comes with STONITHd. - -STONITH is an acronym for Shoot-The-Other-Node-In-The-Head and is -usually implemented with a remote power switch. - -In Pacemaker, STONITH devices are modeled as resources (and configured -in the CIB) to enable them to be easily monitored for failure, however -STONITHd takes care of understanding the STONITH topology such that -its clients simply request a node be fenced and it does the rest. - -== Types of Pacemaker Clusters == - -Pacemaker makes no assumptions about your environment, this allows it -to support practically any -http://en.wikipedia.org/wiki/High-availability_cluster#Node_configurations[redundancy -configuration] including Active/Active, Active/Passive, N+1, N+M, -N-to-1 and N-to-N. - -.Active/Passive Redundancy -image::images/pcmk-active-passive.png["Active/Passive Redundancy",width="10cm",height="7.5cm",align="center"] - -Two-node Active/Passive clusters using Pacemaker and DRBD are a -cost-effective solution for many High Availability situations. - -.Shared Failover -image::images/pcmk-shared-failover.png["Shared Failover",width="10cm",height="7.5cm",align="center"] - -By supporting many nodes, Pacemaker can dramatically reduce hardware -costs by allowing several active/passive clusters to be combined and -share a common backup node - -.N to N Redundancy -image::images/pcmk-active-active.png["N to N Redundancy",width="10cm",height="7.5cm",align="center"] - -When shared storage is available, every node can potentially be used -for failover. Pacemaker can even run multiple copies of services to -spread out the workload. +include::../../shared/en-US/pacemaker-intro.txt[] diff --git a/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt b/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt index efd2f7a5b2..18b320b222 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt @@ -1,361 +1,354 @@ = Multi-Site Clusters and Tickets = [[Multisite]] == Abstract == Apart from local clusters, Pacemaker also supports multi-site clusters. That means you can have multiple, geographically dispersed sites with a local cluster each. Failover between these clusters can be coordinated by a higher level entity, the so-called `CTR (Cluster Ticket Registry)`. == Challenges for Multi-Site Clusters == Typically, multi-site environments are too far apart to support synchronous communication between the sites and synchronous data replication. That leads to the following challenges: - How to make sure that a cluster site is up and running? - How to make sure that resources are only started once? - How to make sure that quorum can be reached between the different sites and a split brain scenario can be avoided? - How to manage failover between the sites? - How to deal with high latency in case of resources that need to be stopped? In the following sections, learn how to meet these challenges. == Conceptual Overview == Multi-site clusters can be considered as “overlay” clusters where each cluster site corresponds to a cluster node in a traditional cluster. The overlay cluster can be managed by a `CTR (Cluster Ticket Registry)` mechanism. It guarantees that the cluster resources will be highly available across different cluster sites. This is achieved by using so-called `tickets` that are treated as failover domain between cluster sites, in case a site should be down. The following list explains the individual components and mechanisms that were introduced for multi-site clusters in more detail. === Components and Concepts === ==== Ticket ==== "Tickets" are, essentially, cluster-wide attributes. A ticket grants the right to run certain resources on a specific cluster site. Resources can be bound to a certain ticket by `rsc_ticket` dependencies. Only if the ticket is available at a site, the respective resources are started. Vice versa, if the ticket is revoked, the resources depending on that ticket need to be stopped. The ticket thus is similar to a 'site quorum'; i.e., the permission to manage/own resources associated with that site. (One can also think of the current `have-quorum` flag as a special, cluster-wide ticket that is granted in case of node majority.) These tickets can be granted/revoked either manually by administrators (which could be the default for the classic enterprise clusters), or via an automated `CTR` mechanism described further below. A ticket can only be owned by one site at a time. Initially, none of the sites has a ticket. Each ticket must be granted once by the cluster administrator. The presence or absence of tickets for a site is stored in the CIB as a cluster status. With regards to a certain ticket, there are only two states for a site: `true` (the site has the ticket) or `false` (the site does not have the ticket). The absence of a certain ticket (during the initial state of the multi-site cluster) is also reflected by the value `false`. ==== Dead Man Dependency ==== A site can only activate the resources safely if it can be sure that the other site has deactivated them. However after a ticket is revoked, it can take a long time until all resources depending on that ticket are stopped "cleanly", especially in case of cascaded resources. To cut that process short, the concept of a `Dead Man Dependency` was introduced: - If the ticket is revoked from a site, the nodes that are hosting dependent resources are fenced. This considerably speeds up the recovery process of the cluster and makes sure that resources can be migrated more quickly. This can be configured by specifying a `loss-policy="fence"` in `rsc_ticket` constraints. ==== CTR (Cluster Ticket Registry) ==== This is for those scenarios where the tickets management is supposed to be automatic (instead of the administrator revoking the ticket somewhere, waiting for everything to stop, and then granting it on the desired site). A `CTR` is a network daemon that handles granting, revoking, and timing out "tickets". The participating clusters would run the daemons that would connect to each other, exchange information on their connectivity details, and vote on which site gets which ticket(s). A ticket would only be granted to a site once they can be sure that it has been relinquished by the previous owner, which would need to be implemented via a timer in most scenarios. If a site loses connection to its peers, its tickets time out and recovery occurs. After the connection timeout plus the recovery timeout has passed, the other sites are allowed to re-acquire the ticket and start the resources again. This can also be thought of as a "quorum server", except that it is not a single quorum ticket, but several. ==== Configuration Replication ==== As usual, the CIB is synchronized within each cluster, but it is not synchronized across cluster sites of a multi-site cluster. You have to configure the resources that will be highly available across the multi-site cluster for every site accordingly. == Configuring Ticket Dependencies == The `rsc_ticket` constraint lets you specify the resources depending on a certain ticket. Together with the constraint, you can set a `loss-policy` that defines what should happen to the respective resources if the ticket is revoked. The attribute `loss-policy` can have the following values: fence:: Fence the nodes that are running the relevant resources. stop:: Stop the relevant resources. freeze:: Do nothing to the relevant resources. demote:: Demote relevant resources that are running in master mode to slave mode. An example to configure a `rsc_ticket` constraint: [source,XML] ------- ------- This creates a constraint with the ID `rsc1-req-ticketA`. It defines that the resource `rsc1` depends on `ticketA` and that the node running the resource should be fenced in case `ticketA` is revoked. If resource `rsc1` was a multi-state resource that can run in master or slave mode, you may want to configure that only `rsc1's` master mode depends on `ticketA`. With the following configuration, `rsc1` will be demoted to slave mode if `ticketA` is revoked: [source,XML] ------- ------- You can create more `rsc_ticket` constraints to let multiple resources depend on the same ticket. `rsc_ticket` also supports resource sets. So one can easily list all the resources in one `rsc_ticket` constraint. For example: [source,XML] ------- ------- In the example, there are two resource sets for listing the resources with different `roles` in one `rsc_ticket` constraint. There's no dependency between the two resource sets. And there's no dependency among the resources within a resource set. Each of the resources just depends on `ticketA`. Referencing resource templates in `rsc_ticket` constraints, and even referencing them within resource sets, is also supported. If you want other resources to depend on further tickets, create as many constraints as necessary with `rsc_ticket`. == Managing Multi-Site Clusters == === Granting and Revoking Tickets Manually === You can grant tickets to sites or revoke them from sites manually. Though if you want to re-distribute a ticket, you should wait for the dependent resources to cleanly stop at the previous site before you grant the ticket to another desired site. Use the `crm_ticket` command line tool to grant and revoke tickets. To grant a ticket to this site: -[source,C] ------- # crm_ticket --ticket ticketA --grant ------- To revoke a ticket from this site: -[source,C] ------- # crm_ticket --ticket ticketA --revoke ------- [IMPORTANT] ==== If you are managing tickets manually. Use the `crm_ticket` command with great care as they cannot help verify if the same ticket is already granted elsewhere. ==== === Granting and Revoking Tickets via a Cluster Ticket Registry === ==== Booth ==== Booth is an implementation of `Cluster Ticket Registry` or so-called `Cluster Ticket Manager`. Booth is the instance managing the ticket distribution and thus, the failover process between the sites of a multi-site cluster. Each of the participating clusters and arbitrators runs a service, the boothd. It connects to the booth daemons running at the other sites and exchanges connectivity details. Once a ticket is granted to a site, the booth mechanism will manage the ticket automatically: If the site which holds the ticket is out of service, the booth daemons will vote which of the other sites will get the ticket. To protect against brief connection failures, sites that lose the vote (either explicitly or implicitly by being disconnected from the voting body) need to relinquish the ticket after a time-out. Thus, it is made sure that a ticket will only be re-distributed after it has been relinquished by the previous site. The resources that depend on that ticket will fail over to the new site holding the ticket. The nodes that have run the resources before will be treated according to the `loss-policy` you set within the `rsc_ticket` constraint. Before the booth can manage a certain ticket within the multi-site cluster, you initially need to grant it to a site manually via `booth client` command. After you have initially granted a ticket to a site, the booth mechanism will take over and manage the ticket automatically. [IMPORTANT] ==== The `booth client` command line tool can be used to grant, list, or revoke tickets. The `booth client` commands work on any machine where the booth daemon is running. If you are managing tickets via `Booth`, only use `booth client` for manual intervention instead of `crm_ticket`. That can make sure the same ticket will only be owned by one cluster site at a time. ==== Booth includes an implementation of http://en.wikipedia.org/wiki/Paxos_algorithm['Paxos'] and 'Paxos Lease' algorithm, which guarantees the distributed consensus among different cluster sites. [NOTE] ==== `Arbitrator` Each site runs one booth instance that is responsible for communicating with the other sites. If you have a setup with an even number of sites, you need an additional instance to reach consensus about decisions such as failover of resources across sites. In this case, add one or more arbitrators running at additional sites. Arbitrators are single machines that run a booth instance in a special mode. As all booth instances communicate with each other, arbitrators help to make more reliable decisions about granting or revoking tickets. An arbitrator is especially important for a two-site scenario: For example, if site `A` can no longer communicate with site `B`, there are two possible causes for that: - `A` network failure between `A` and `B`. - Site `B` is down. However, if site `C` (the arbitrator) can still communicate with site `B`, site `B` must still be up and running. ==== ===== Requirements ===== - All clusters that will be part of the multi-site cluster must be based on Pacemaker. - Booth must be installed on all cluster nodes and on all arbitrators that will be part of the multi-site cluster. The most common scenario is probably a multi-site cluster with two sites and a single arbitrator on a third site. However, technically, there are no limitations with regards to the number of sites and the number of arbitrators involved. Nodes belonging to the same cluster site should be synchronized via NTP. However, time synchronization is not required between the individual cluster sites. === General Management of Tickets === Display the information of tickets: -[source,C] ------- # crm_ticket --info ------- Or you can monitor them with: -[source,C] ------- # crm_mon --tickets ------- Display the rsc_ticket constraints that apply to a ticket: -[source,C] ------- # crm_ticket --ticket ticketA --constraints ------- When you want to do maintenance or manual switch-over of a ticket, the ticket could be revoked from the site for any reason, which would trigger the loss-policies. If `loss-policy="fence"`, the dependent resources could not be gracefully stopped/demoted, and even, other unrelated resources could be impacted. The proper way is making the ticket `standby` first with: -[source,C] ------- # crm_ticket --ticket ticketA --standby ------- Then the dependent resources will be stopped or demoted gracefully without triggering the loss-policies. If you have finished the maintenance and want to activate the ticket again, you can run: -[source,C] ------- # crm_ticket --ticket ticketA --activate ------- == For more information == `Multi-site Clusters` http://doc.opensuse.org/products/draft/SLE-HA/SLE-ha-guide_sd_draft/cha.ha.geo.html `Booth` https://github.com/ClusterLabs/booth diff --git a/doc/Pacemaker_Explained/en-US/Ch-Nodes.txt b/doc/Pacemaker_Explained/en-US/Ch-Nodes.txt index 16bf13d9c7..cc4add1c65 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Nodes.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Nodes.txt @@ -1,220 +1,223 @@ = Cluster Nodes = == Defining a Cluster Node == Each node in the cluster will have an entry in the nodes section containing its UUID, uname, and type. .Example Heartbeat cluster node entry ====== [source,XML] ====== .Example Corosync cluster node entry ====== [source,XML] ====== In normal circumstances, the admin should let the cluster populate this information automatically from the communications and membership data. However for Heartbeat, one can use the `crm_uuid` tool to read an existing UUID or define a value before the cluster starts. [[s-node-name]] == Where Pacemaker Gets the Node Name == Traditionally, Pacemaker required nodes to be referred to by the value returned by `uname -n`. This can be problematic for services that require the `uname -n` to be a specific value (ie. for a licence file). Since version 2.0.0 of Pacemaker, this requirement has been relaxed for clusters using Corosync 2.0 or later. The name Pacemaker uses is: . The value stored in 'corosync.conf' under +ring0_addr+ in the +nodelist+, if it does not contain an IP address; otherwise . The value stored in 'corosync.conf' under +name+ in the +nodelist+; otherwise . The value of `uname -n` Pacemaker provides the `crm_node -n` command which displays the name used by a running cluster. If a Corosync nodelist is used, `crm_node --name-for-id $number` is also available to display the name used by the node with the corosync +nodeid+ of '$number', for example: `crm_node --name-for-id 2`. [[s-node-attributes]] == Describing a Cluster Node == indexterm:[Node,attribute] Beyond the basic definition of a node the administrator can also describe the node's attributes, such as how much RAM, disk, what OS or kernel version it has, perhaps even its physical location. This information can then be used by the cluster when deciding where to place resources. For more information on the use of node attributes, see <>. Node attributes can be specified ahead of time or populated later, when the cluster is running, using `crm_attribute`. Below is what the node's definition would look like if the admin ran the command: .The result of using crm_attribute to specify which kernel pcmk-1 is running ====== -[source,C] ------- # crm_attribute --type nodes --node-uname pcmk-1 --attr-name kernel --attr-value `uname -r` ------- [source,XML] ------- ------- ====== A simpler way to determine the current value of an attribute is to use `crm_attribute` command again: -[source,C] +---- # crm_attribute --type nodes --node-uname pcmk-1 --attr-name kernel --get-value +---- By specifying `--type nodes` the admin tells the cluster that this attribute is persistent. There are also transient attributes which are kept in the status section which are "forgotten" whenever the node rejoins the cluster. The cluster uses this area to store a record of how many times a resource has failed on that node but administrators can also read and write to this section by specifying `--type status`. == Corosync == === Adding a New Corosync Node === indexterm:[Corosync,Add Cluster Node] indexterm:[Add Cluster Node,Corosync] Adding a new node is as simple as installing Corosync and Pacemaker, and copying '/etc/corosync/corosync.conf' and '/etc/corosync/authkey' (if it exists) from an existing node. You may need to modify the +mcastaddr+ option to match the new node's IP address. If a log message containing "Invalid digest" appears from Corosync, the keys are not consistent between the machines. === Removing a Corosync Node === indexterm:[Corosync,Remove Cluster Node] indexterm:[Remove Cluster Node,Corosync] Because the messaging and membership layers are the authoritative source for cluster nodes, deleting them from the CIB is not a reliable solution. First one must arrange for corosync to forget about the node (_pcmk-1_ in the example below). On the host to be removed: . Stop the cluster: `/etc/init.d/corosync stop` Next, from one of the remaining active cluster nodes: . Tell Pacemaker to forget about the removed host: + -[source,C] +---- # crm_node -R pcmk-1 +---- + This includes deleting the node from the CIB [NOTE] ====== This proceedure only works for versions after 1.1.8 ====== === Replacing a Corosync Node === indexterm:[Corosync,Replace Cluster Node] indexterm:[Replace Cluster Node,Corosync] The five-step guide to replacing an existing cluster node: . Make sure the old node is completely stopped . Give the new machine the same hostname and IP address as the old one . Install the cluster software :-) . Copy '/etc/corosync/corosync.conf' and '/etc/corosync/authkey' (if it exists) to the new node . Start the new cluster node If a log message containing "Invalid digest" appears from Corosync, the keys are not consistent between the machines. == CMAN == === Adding a New CMAN Node === indexterm:[CMAN,Add Cluster Node] indexterm:[Add Cluster Node,CMAN] === Removing a CMAN Node === indexterm:[CMAN,Remove Cluster Node] indexterm:[Remove Cluster Node,CMAN] == Heartbeat == === Adding a New Heartbeat Node === indexterm:[Heartbeat,Add Cluster Node] indexterm:[Add Cluster Node,Heartbeat] Provided you specified +autojoin any+ in 'ha.cf', adding a new node is as simple as installing heartbeat and copying 'ha.cf' and 'authkeys' from an existing node. If you don't want to use +autojoin+, then after setting up 'ha.cf' and 'authkeys', you must use `hb_addnode` before starting the new node. === Removing a Heartbeat Node === indexterm:[Heartbeat,Remove Cluster Node] indexterm:[Remove Cluster Node,Heartbeat] Because the messaging and membership layers are the authoritative source for cluster nodes, deleting them from the CIB is not a reliable solution. First one must arrange for Heartbeat to forget about the node (pcmk-1 in the example below). On the host to be removed: . Stop the cluster: `/etc/init.d/corosync stop` Next, from one of the remaining active cluster nodes: . Tell Heartbeat the node should be removed -[source,C] +---- # hb_delnode pcmk-1 +---- . Tell Pacemaker to forget about the removed host: -[source,C] +---- # crm_node -R pcmk-1 +---- [NOTE] ====== This proceedure only works for versions after 1.1.8 ====== === Replacing a Heartbeat Node === indexterm:[Heartbeat,Replace Cluster Node] indexterm:[Replace Cluster Node,Heartbeat] The seven-step guide to replacing an existing cluster node: . Make sure the old node is completely stopped . Give the new machine the same hostname as the old one . Go to an active cluster node and look up the UUID for the old node in '/var/lib/heartbeat/hostcache' . Install the cluster software . Copy 'ha.cf' and 'authkeys' to the new node . On the new node, populate it's UUID using `crm_uuid -w` and the UUID from step 2 . Start the new cluster node diff --git a/doc/Pacemaker_Explained/en-US/Ch-Options.txt b/doc/Pacemaker_Explained/en-US/Ch-Options.txt index 3a6ee0b0e2..6f9eecda05 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Options.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Options.txt @@ -1,387 +1,393 @@ = Cluster Options = == Special Options == The reason for these fields to be placed at the top level instead of with the rest of cluster options is simply a matter of parsing. These options are used by the configuration database which is, by design, mostly ignorant of the content it holds. So the decision was made to place them in an easy to find location. == Configuration Version == indexterm:[Configuration Version,Cluster] indexterm:[Cluster,Option,Configuration Version] When a node joins the cluster, the cluster will perform a check to see who has the best configuration based on the fields below. It then asks the node with the highest (+admin_epoch+, +epoch+, +num_updates+) tuple to replace the configuration on all the nodes - which makes setting them, and setting them correctly, very important. .Configuration Version Properties [width="95%",cols="2m,5<",options="header",align="center"] |========================================================= |Field |Description | admin_epoch | indexterm:[admin_epoch,Cluster Option] indexterm:[Cluster,Option,admin_epoch] Never modified by the cluster. Use this to make the configurations on any inactive nodes obsolete. _Never set this value to zero_, in such cases the cluster cannot tell the difference between your configuration and the "empty" one used when nothing is found on disk. | epoch | indexterm:[epoch,Cluster Option] indexterm:[Cluster,Option,epoch] Incremented every time the configuration is updated (usually by the admin) | num_updates | indexterm:[num_updates,Cluster Option] indexterm:[Cluster,Option,num_updates] Incremented every time the configuration or status is updated (usually by the cluster) |========================================================= == Other Fields == .Properties Controlling Validation [width="95%",cols="2m,5<",options="header",align="center"] |========================================================= |Field |Description | validate-with | indexterm:[validate-with,Cluster Option] indexterm:[Cluster,Option,validate-with] Determines the type of validation being done on the configuration. If set to "none", the cluster will not verify that updates conform to the DTD (nor reject ones that don't). This option can be useful when operating a mixed version cluster during an upgrade. |========================================================= == Fields Maintained by the Cluster == .Properties Maintained by the Cluster [width="95%",cols="2m,5<",options="header",align="center"] |========================================================= |Field |Description |cib-last-written | indexterm:[cib-last-written,Cluster Property] indexterm:[Cluster,Property,cib-last-written] Indicates when the configuration was last written to disk. Informational purposes only. |dc-uuid | indexterm:[dc-uuid,Cluster Property] indexterm:[Cluster,Property,dc-uuid] Indicates which cluster node is the current leader. Used by the cluster when placing resources and determining the order of some events. |have-quorum | indexterm:[have-quorum,Cluster Property] indexterm:[Cluster,Property,have-quorum] Indicates if the cluster has quorum. If false, this may mean that the cluster cannot start resources or fence other nodes. See +no-quorum-policy+ below. | dc-version | indexterm:[dc-version,Cluster Property] indexterm:[Cluster,Property,dc-version] Version of Pacemaker on the cluster's DC. Often includes the hash which identifies the exact Git changeset it was built from. Used for diagnostic purposes. | cluster-infrastructure | indexterm:[cluster-infrastructure,Cluster Property] indexterm:[Cluster,Property,cluster-infrastructure] The messaging stack on which Pacemaker is currently running. Used for informational and diagnostic purposes. | expected-quorum-votes | indexterm:[expected-quorum-votes,Cluster Property] indexterm:[Cluster,Property,expected-quorum-votes] The number of nodes expected to be in the cluster Used to calculate quorum in Corosync 1.x (not CMAN) based clusters. |========================================================= Note that although these fields can be written to by the admin, in most cases the cluster will overwrite any values specified by the admin with the "correct" ones. To change the +admin_epoch+, for example, one would use: -[source,C] +---- # cibadmin --modify --crm_xml '' +---- A complete set of fields will look something like this: .An example of the fields set for a cib object ====== [source,XML] ------- ------- ====== == Cluster Options == Cluster options, as you might expect, control how the cluster behaves when confronted with certain situations. They are grouped into sets and, in advanced configurations, there may be more than one. footnote:[This will be described later in the section on <> where we will show how to have the cluster use different sets of options during working hours (when downtime is usually to be avoided at all costs) than it does during the weekends (when resources can be moved to the their preferred hosts without bothering end users)] For now we will describe the simple case where each option is present at most once. == Available Cluster Options == .Cluster Options [width="95%",cols="5m,2,11<",options="header",align="center"] |========================================================= |Option |Default |Description | batch-limit | 30 | indexterm:[batch-limit,Cluster Option] indexterm:[Cluster,Option,batch-limit] The number of jobs that the TE is allowed to execute in parallel. The "correct" value will depend on the speed and load of your network and cluster nodes. | migration-limit | -1 (unlimited) | indexterm:[migration-limit,Cluster Option] indexterm:[Cluster,Option,migration-limit] The number of migration jobs that the TE is allowed to execute in parallel on a node. | no-quorum-policy | stop | indexterm:[no-quorum-policy,Cluster Option] indexterm:[Cluster,Option,no-quorum-policy] What to do when the cluster does not have quorum. Allowed values: * ignore - continue all resource management * freeze - continue resource management, but don't recover resources from nodes not in the affected partition * stop - stop all resources in the affected cluster partition * suicide - fence all nodes in the affected cluster partition | symmetric-cluster | TRUE | indexterm:[symmetric-cluster,Cluster Option] indexterm:[Cluster,Option,symmetric-cluster] Can all resources run on any node by default? | stonith-enabled | TRUE | indexterm:[stonith-enabled,Cluster Option] indexterm:[Cluster,Option,stonith-enabled] Should failed nodes and nodes with resources that can't be stopped be shot? If you value your data, set up a STONITH device and enable this. If true, or unset, the cluster will refuse to start resources unless one or more STONITH resources have been configured also. | stonith-action | reboot | indexterm:[stonith-action,Cluster Option] indexterm:[Cluster,Option,stonith-action] Action to send to STONITH device. Allowed values: reboot, off. The value 'poweroff' is also allowed, but is only used for legacy devices. | cluster-delay | 60s | indexterm:[cluster-delay,Cluster Option] indexterm:[Cluster,Option,cluster-delay] Round trip delay over the network (excluding action execution). The "correct" value will depend on the speed and load of your network and cluster nodes. | stop-all-resources | FALSE | indexterm:[stop-all-resources,Cluster Option] indexterm:[Cluster,Option,stop-all-resources] Should the cluster stop all resources | resources-orphan-resources | TRUE | indexterm:[stop-orphan-resources,Cluster Option] indexterm:[Cluster,Option,stop-orphan-resources] Should deleted resources be stopped? | stop-orphan-actions | TRUE | indexterm:[stop-orphan-actions,Cluster Option] indexterm:[Cluster,Option,stop-orphan-actions] Should deleted actions be cancelled? | start-failure-is-fatal | TRUE | indexterm:[start-failure-is-fatal,Cluster Option] indexterm:[Cluster,Option,start-failure-is-fatal] When set to FALSE, the cluster will instead use the resource's +failcount+ and value for +resource-failure-stickiness+. | pe-error-series-max | -1 (all) | indexterm:[pe-error-series-max,Cluster Option] indexterm:[Cluster,Option,pe-error-series-max] The number of PE inputs resulting in ERRORs to save. Used when reporting problems. | pe-warn-series-max | -1 (all) | indexterm:[pe-warn-series-max,Cluster Option] indexterm:[Cluster,Option,pe-warn-series-max] The number of PE inputs resulting in WARNINGs to save. Used when reporting problems. | pe-input-series-max | -1 (all) | indexterm:[pe-input-series-max,Cluster Option] indexterm:[Cluster,Option,pe-input-series-max] The number of "normal" PE inputs to save. Used when reporting problems. |default-resource-stickiness | 0 | indexterm:[default-resource-stickiness,Cluster Option] indexterm:[Cluster,Option,default-resource-stickiness] +Deprecated:+ See <> instead | is-managed-default | TRUE | indexterm:[is-managed-default,Cluster Option] indexterm:[Cluster,Option,is-managed-default] +Deprecated:+ See <> instead | maintenance-mode | FALSE | indexterm:[maintenance-mode,Cluster Option] indexterm:[Cluster,Option,maintenance-mode] Should the cluster monitor resources and start/stop them as required | stonith-timeout | 60s | indexterm:[stonith-timeout,Cluster Option] indexterm:[Cluster,Option,stonith-timeout] How long to wait for the STONITH action to complete | default-action-timeout | 20s | indexterm:[default-action-timeout,Cluster Option] indexterm:[Cluster,Option,default-action-timeout] +Deprecated:+ See <> instead | dc-deadtime | 20s | indexterm:[dc-deadtime,Cluster Option] indexterm:[Cluster,Option,dc-deadtime] How long to wait for a response from other nodes during startup. The "correct" value will depend on the speed/load of your network and the type of switches used. | cluster-recheck-interval | 15min | indexterm:[cluster-recheck-interval,Cluster Option] indexterm:[Cluster,Option,cluster-recheck-interval] Polling interval for time based changes to options, resource parameters and constraints. The Cluster is primarily event driven, however the configuration can have elements that change based on time. To ensure these changes take effect, we can optionally poll the cluster's status for changes. Allowed values: Zero disables polling. Positive values are an interval in seconds (unless other SI units are specified. eg. 5min) | election-timeout | 2min | indexterm:[election-timeout,Cluster Option] indexterm:[Cluster,Option,election-timeout] +Advanced Use Only+ If need to adjust this value, it probably indicates the presence of a bug. | shutdown-escalation | 20min | indexterm:[shutdown-escalation,Cluster Option] indexterm:[Cluster,Option,shutdown-escalation] +Advanced Use Only+ If need to adjust this value, it probably indicates the presence of a bug. | crmd-integration-timeout | 3min | indexterm:[crmd-integration-timeout,Cluster Option] indexterm:[Cluster,Option,crmd-integration-timeout] +Advanced Use Only+ If need to adjust this value, it probably indicates the presence of a bug. | crmd-finalization-timeout | 30min | indexterm:[crmd-finalization-timeout,Cluster Option] indexterm:[Cluster,Option,crmd-finalization-timeout] +Advanced Use Only+ If need to adjust this value, it probably indicates the presence of a bug. | crmd-transition-delay | | indexterm:[crmd-transition-delay,Cluster Option] indexterm:[Cluster,Option,crmd-transition-delay] +Advanced Use Only+ Enabling this option will slow down cluster recovery under all conditions. Delay cluster recovery for the configured interval to allow for additional/related events to occur. Useful if your configuration is sensitive to the order in which ping updates arrive. |========================================================= You can always obtain an up-to-date list of cluster options, including their default values, by running the `man pengine` and `man crmd` commands. == Querying and Setting Cluster Options == indexterm:[Querying,Cluster Option] indexterm:[Setting,Cluster Option] indexterm:[Cluster,Querying Options] indexterm:[Cluster,Setting Options] Cluster options can be queried and modified using the `crm_attribute` tool. To get the current value of +cluster-delay+, simply use: -[source,C] +---- # crm_attribute --attr-name cluster-delay --get-value +---- which is more simply written as -[source,C] +---- # crm_attribute --get-value -n cluster-delay +---- If a value is found, you'll see a result like this: -[source,C] +---- # crm_attribute --get-value -n cluster-delay name=cluster-delay value=60s +---- However, if no value is found, the tool will display an error: -[source,C] +---- # crm_attribute --get-value -n clusta-deway` name=clusta-deway value=(null) Error performing operation: The object/attribute does not exist +---- To use a different value, eg. +30+, simply run: -[source,C] +---- # crm_attribute --attr-name cluster-delay --attr-value 30s +---- To go back to the cluster's default value you can delete the value, for example with this command: -[source,C] +---- # crm_attribute --attr-name cluster-delay --delete-attr +---- == When Options are Listed More Than Once == If you ever see something like the following, it means that the option you're modifying is present more than once. .Deleting an option that is listed twice ======= -[source,C] ------ # crm_attribute --attr-name batch-limit --delete-attr Multiple attributes match name=batch-limit in crm_config: Value: 50 (set=cib-bootstrap-options, id=cib-bootstrap-options-batch-limit) Value: 100 (set=custom, id=custom-batch-limit) Please choose from one of the matches above and supply the 'id' with --attr-id ------- ======= In such cases follow the on-screen instructions to perform the requested action. To determine which value is currently being used by the cluster, please refer to <>. diff --git a/doc/Pacemaker_Explained/en-US/Ch-Resource-Templates.txt b/doc/Pacemaker_Explained/en-US/Ch-Resource-Templates.txt index 5c34ae7ef7..3a0eaf7a0f 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Resource-Templates.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Resource-Templates.txt @@ -1,216 +1,218 @@ = Resource Templates = == Abstract == If you want to create lots of resources with similar configurations, defining a resource template simplifies the task. Once defined, it can be referenced in primitives or in certain types of constraints. == Configuring Resources with Templates == The primitives referencing the template will inherit all meta attributes, instance attributes, utilization attributes and operations defined in the template. And you can define specific attributes and operations for any of the primitives. If any of these are defined in both the template and the primitive, the values defined in the primitive will take precedence over the ones defined in the template. Hence, resource templates help to reduce the amount of configuration work. If any changes are needed, they can be done to the template definition and will take effect globally in all resource definitions referencing that template. Resource templates have a similar syntax like primitives. For example: [source,XML] ---- ---- Once you defined the new resource template, you can use it in primitives: [source,XML] ---- ---- The new primitive `vm1` is going to inherit everything from the `vm-template`. For example, the equivalent of the above two would be: [source,XML] ---- ---- If you want to overwrite some attributes or operations, add them to the particular primitive's definition. For instance, the following new primitive `vm2` has special attribute values. Its `monitor` operation has a longer `timeout` and `interval`, and the primitive has an additional `stop` operation. [source,XML] ---- ---- The following command shows the resulting definition of a resource: -[source,C] +---- # crm_resource --query-xml --resource vm2 +---- The following command shows its raw definition in cib: -[source,C] +---- # crm_resource --query-xml-raw --resource vm2 +---- == Referencing Templates in Constraints == A resource template can be referenced in the following types of constraints: - `order` constraints - `colocation` constraints, - `rsc_ticket` constraints (for multi-site clusters). Resource templates referenced in constraints stand for all primitives which are derived from that template. This means, the constraint applies to all primitive resources referencing the resource template. Referencing resource templates in constraints is an alternative to resource sets and can simplify the cluster configuration considerably. For example: [source,XML] is the equivalent of the following constraint configuration: [source,XML] ---- ---- [NOTE] ====== In a colocation constraint, only one template may be referenced from either `rsc` or `with-rsc`, and the other reference must be a regular resource. ====== Resource templates can also be referenced in resource sets. For example: [source,XML] ---- ---- is the equivalent of the following constraint configuration: [source,XML] ---- ---- If the resources referencing the template can run in parallel: [source,XML] ---- ---- is the equivalent of the following constraint configuration: [source,XML] ---- ---- diff --git a/doc/Pacemaker_Explained/en-US/Ch-Resources.txt b/doc/Pacemaker_Explained/en-US/Ch-Resources.txt index fb88c15d44..784ef720ad 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Resources.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Resources.txt @@ -1,715 +1,718 @@ = Cluster Resources = == What is a Cluster Resource == indexterm:[Resource] The role of a resource agent is to abstract the service it provides and present a consistent view to the cluster, which allows the cluster to be agnostic about the resources it manages. The cluster doesn't need to understand how the resource works because it relies on the resource agent to do the right thing when given a +start+, +stop+ or +monitor+ command. For this reason it is crucial that resource agents are well tested. Typically resource agents come in the form of shell scripts, however they can be written using any technology (such as C, Python or Perl) that the author is comfortable with. [[s-resource-supported]] == Supported Resource Classes == indexterm:[Resource,class] There are six classes of agents supported by Pacemaker: * OCF * LSB * Upstart * Systemd * Fencing * Service * Nagios indexterm:[Resource,Heartbeat] indexterm:[Heartbeat,Resources] Version 1 of Heartbeat came with its own style of resource agents and it is highly likely that many people have written their own agents based on its conventions. footnote:[ See http://wiki.linux-ha.org/HeartbeatResourceAgent for more information ] Although deprecated with the release of Heartbeat v2, they were supported by Pacemaker up until the release of 1.1.8 to enable administrators to continue to use these agents. === Open Cluster Framework === indexterm:[Resource,OCF] indexterm:[OCF,Resources] indexterm:[Open Cluster Framework,Resources] The OCF standard footnote:[ http://www.opencf.org/cgi-bin/viewcvs.cgi/specs/ra/resource-agent-api.txt?rev=HEAD - at least as it relates to resource agents. ] footnote:[ The Pacemaker implementation has been somewhat extended from the OCF Specs, but none of those changes are incompatible with the original OCF specification. ] is basically an extension of the Linux Standard Base conventions for init scripts to: * support parameters, * make them self describing and * extensible OCF specs have strict definitions of the exit codes that actions must return. footnote:[ Included with the cluster is the ocf-tester script, which can be useful in this regard. ] The cluster follows these specifications exactly, and giving the wrong exit code will cause the cluster to behave in ways you will likely find puzzling and annoying. In particular, the cluster needs to distinguish a completely stopped resource from one which is in some erroneous and indeterminate state. Parameters are passed to the script as environment variables, with the special prefix +OCF_RESKEY_+. So, a parameter which the user thinks of as ip it will be passed to the script as +OCF_RESKEY_ip+. The number and purpose of the parameters is completely arbitrary, however your script should advertise any that it supports using the +meta-data+ command. The OCF class is the most preferred one as it is an industry standard, highly flexible (allowing parameters to be passed to agents in a non-positional manner) and self-describing. For more information, see the http://www.linux-ha.org/wiki/OCF_Resource_Agents[reference] and <>. === Linux Standard Base === indexterm:[Resource,LSB] indexterm:[LSB,Resources] indexterm:[Linux Standard Base,Resources] LSB resource agents are those found in '/etc/init.d'. Generally they are provided by the OS/distribution and, in order to be used with the cluster, they must conform to the LSB Spec. footnote:[ See http://refspecs.linux-foundation.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html for the LSB Spec (as it relates to init scripts). ] Many distributions claim LSB compliance but ship with broken init scripts. For details on how to check if your init script is LSB-compatible, see <>. The most common problems are: * Not implementing the status operation at all * Not observing the correct exit status codes for start/stop/status actions * Starting a started resource returns an error (this violates the LSB spec) * Stopping a stopped resource returns an error (this violates the LSB spec) === Systemd === indexterm:[Resource,Systemd] indexterm:[Systemd,Resources] Some newer distributions have replaced the old http://en.wikipedia.org/wiki/Init#SysV-style[SYS-V] style of initialization daemons (and scripts) with an alternative called http://www.freedesktop.org/wiki/Software/systemd[Systemd]. Pacemaker is able to manage these services _if they are present_. Instead of +init scripts+, systemd has +unit files+. Generally the services (or unit files) are provided by the OS/distribution but there are some instructions for converting from init scripts at: http://0pointer.de/blog/projects/systemd-for-admins-3.html [NOTE] ====== Remember to make sure the computer is +not+ configured to start any services at boot time that should be controlled by the cluster. ====== === Upstart === indexterm:[Resource,Upstart] indexterm:[Upstart,Resources] Some newer distributions have replaced the old http://en.wikipedia.org/wiki/Init#SysV-style[SYS-V] style of initialization daemons (and scripts) with an alternative called http://upstart.ubuntu.com[Upstart]. Pacemaker is able to manage these services _if they are present_. Instead of +init scripts+, upstart has +jobs+. Generally the services (or jobs) are provided by the OS/distribution. [NOTE] ====== Remember to make sure the computer is +not+ configured to start any services at boot time that should be controlled by the cluster. ====== === System Services === indexterm:[Resource,System Services] indexterm:[System Service,Resources] Since there are now many "common" types of system services (+systemd+, +upstart+, and +lsb+), Pacemaker supports a special alias which intelligently figures out which one applies to a given cluster node. This is particularly useful when the cluster contains a mix of +systemd+, +upstart+, and +lsb+. In order, Pacemaker will try to find the named service as: . an LSB (SYS-V) init script . a Systemd unit file . an Upstart job === STONITH === indexterm:[Resource,STONITH] indexterm:[STONITH,Resources] There is also an additional class, STONITH, which is used exclusively for fencing related resources. This is discussed later in <>. === Nagios Plugins === indexterm:[Resource,Nagios Plugins] indexterm:[Nagios Plugins,Resources] Nagios plugins allow us to monitor services on the remote hosts. http://nagiosplugins.org[Nagios Plugins]. Pacemaker is able to do remote monitoring with the plugins _if they are present_. An use case is to configure them as resources belonging to a resource container, which usually is a VM, and the container will be restarted if any of them has failed. While they can also be configured as ordinary resources to be just used for monitoring hosts or services via network. The supported parameters are same as the long options of a nagios plugin. [[primitive-resource]] == Resource Properties == These values tell the cluster which script to use for the resource, where to find that script and what standards it conforms to. .Properties of a Primitive Resource [width="95%",cols="1m,6<",options="header",align="center"] |========================================================= |Field |Description |id |Your name for the resource indexterm:[id,Resource] indexterm:[Resource,Property,id] |class |The standard the script conforms to. Allowed values: +ocf+, +service+, +upstart+, +systemd+, +lsb+, +stonith+ indexterm:[class,Resource] indexterm:[Resource,Property,class] |type |The name of the Resource Agent you wish to use. Eg. _IPaddr_ or _Filesystem_ indexterm:[type,Resource] indexterm:[Resource,Property,type] |provider |The OCF spec allows multiple vendors to supply the same ResourceAgent. To use the OCF resource agents supplied with Heartbeat, you should specify +heartbeat+ here. indexterm:[provider,Resource] indexterm:[Resource,Property,provider] |========================================================= Resource definitions can be queried with the `crm_resource` tool. For example -[source,C] +---- # crm_resource --resource Email --query-xml +---- might produce: .An example system resource ===== [source,XML] ===== [NOTE] ===== One of the main drawbacks to system services (such as LSB, Systemd and Upstart) resources is that they do not allow any parameters! ===== .An example OCF resource ===== [source,XML] ------- ------- ===== [[s-resource-options]] == Resource Options == Options are used by the cluster to decide how your resource should behave and can be easily set using the `--meta` option of the `crm_resource` command. .Options for a Primitive Resource [width="95%",cols="1m,1,4<",options="header",align="center"] |========================================================= |Field |Default |Description |priority |+0+ |If not all resources can be active, the cluster will stop lower priority resources in order to keep higher priority ones active. indexterm:[priority,Resource Option] indexterm:[Resource,Option,priority] |target-role |+Started+ |What state should the cluster attempt to keep this resource in? Allowed values: * 'Stopped' - Force the resource to be stopped * 'Started' - Allow the resource to be started (In the case of <> resources, they will not promoted to master) * 'Master' - Allow the resource to be started and, if appropriate, promoted indexterm:[target-role,Resource Option] indexterm:[Resource,Option,target-role] |is-managed |+TRUE+ |Is the cluster allowed to start and stop the resource? Allowed values: +true+, +false+ indexterm:[is-managed,Resource Option] indexterm:[Resource,Option,is-managed] |resource-stickiness |Calculated |How much does the resource prefer to stay where it is? Defaults to the value of +resource-stickiness+ in the +rsc_defaults+ section indexterm:[resource-stickiness,Resource Option] indexterm:[Resource,Option,resource-stickiness] |requires |Calculated |Under what conditions can the resource be started. ('Since 1.1.8') Defaults to +fencing+ unless +stonith-enabled+ is 'false' or +class+ is 'stonith' - under those conditions the default is +quorum+. Possible values: * 'nothing' - can always be started * 'quorum' - The cluster can only start this resource if a majority of the configured nodes are active * 'fencing' - The cluster can only start this resource if a majority of the configured nodes are active _and_ any failed or unknown nodes have been powered off. * 'unfencing' - The cluster can only start this resource if a majority of the configured nodes are active _and_ any failed or unknown nodes have been powered off _and_ only on nodes that have been 'unfenced' indexterm: Option[requires,Resource] indexterm:[Resource,Option,requires] |migration-threshold |+INFINITY+ (disabled) |How many failures may occur for this resource on a node, before this node is marked ineligible to host this resource. indexterm:[migration-threshold,Resource Option] indexterm:[Resource,Option,migration-threshold] |failure-timeout |+0+ (disabled) |How many seconds to wait before acting as if the failure had not occurred, and potentially allowing the resource back to the node on which it failed. indexterm:[failure-timeout,Resource Option] indexterm:[Resource,Option,failure-timeout] |multiple-active |+stop_start+ |What should the cluster do if it ever finds the resource active on more than one node. Allowed values: * 'block' - mark the resource as unmanaged * 'stop_only' - stop all active instances and leave them that way * 'stop_start' - stop all active instances and start the resource in one location only indexterm:[multiple-active,Resource Option] indexterm:[Resource,Option,multiple-active] |remote-node |++ (disabled) |The name of the remote-node this resource defines. This both enables the resource as a remote-node and defines the unique name used to identify the remote-node. If no other parameters are set, this value will also be assumed as the hostname to connect to at port 3121. +WARNING+ This value cannot overlap with any resource or node IDs. |remote-port |+3121+ |Configure a custom port to use for the guest connection to pacemaker_remote. |remote-addr |+remote-node+ value used as hostname |The ip address or hostname to connect to if remote-node's name is not the hostname of the guest. |+remote-connect-timeout+ |+60s+ |How long before a pending guest connection will time out. |========================================================= If you performed the following commands on the previous LSB Email resource -[source,C] ------- # crm_resource --meta --resource Email --set-parameter priority --property-value 100 # crm_resource --meta --resource Email --set-parameter multiple-active --property-value block ------- the resulting resource definition would be .An LSB resource with cluster options ===== [source,XML] ------- ------- ===== [[s-resource-defaults]] == Setting Global Defaults for Resource Options == To set a default value for a resource option, simply add it to the +rsc_defaults+ section with `crm_attribute`. Thus, -[source,C] +---- # crm_attribute --type rsc_defaults --attr-name is-managed --attr-value false +---- would prevent the cluster from starting or stopping any of the resources in the configuration (unless of course the individual resources were specifically enabled and had +is-managed+ set to +true+). == Instance Attributes == The scripts of some resource classes (LSB not being one of them) can be given parameters which determine how they behave and which instance of a service they control. If your resource agent supports parameters, you can add them with the `crm_resource` command. For instance -[source,C] +---- # crm_resource --resource Public-IP --set-parameter ip --property-value 1.2.3.4 +---- would create an entry in the resource like this: .An example OCF resource with instance attributes ===== [source,XML] ------- ------- ===== For an OCF resource, the result would be an environment variable called +OCF_RESKEY_ip+ with a value of +1.2.3.4+. The list of instance attributes supported by an OCF script can be found by calling the resource script with the `meta-data` command. The output contains an XML description of all the supported attributes, their purpose and default values. .Displaying the metadata for the Dummy resource agent template ===== -[source,C] ------- # export OCF_ROOT=/usr/lib/ocf # $OCF_ROOT/resource.d/pacemaker/Dummy meta-data ------- [source,XML] ------- 1.0 This is a Dummy Resource Agent. It does absolutely nothing except keep track of whether its running or not. Its purpose in life is for testing and to serve as a template for RA writers. Dummy resource agent Location to store the resource state in. State file Dummy attribute that can be changed to cause a reload Dummy attribute that can be changed to cause a reload ------- ===== == Resource Operations == indexterm:[Resource,Action] === Monitoring Resources for Failure === By default, the cluster will not ensure your resources are still healthy. To instruct the cluster to do this, you need to add a +monitor+ operation to the resource's definition. .An OCF resource with a recurring health check ===== [source,XML] ------- ------- ===== .Properties of an Operation [width="95%",cols="1m,6<",options="header",align="center"] |========================================================= |Field |Description |id |Your name for the action. Must be unique. indexterm:[id,Action Property] indexterm:[Action,Property,id] |name |The action to perform. Common values: +monitor+, +start+, +stop+ indexterm:[name,Action Property] indexterm:[Action,Property,name] |interval |How frequently (in seconds) to perform the operation. Default value: +0+, meaning never. indexterm:[interval,Action Property] indexterm:[Action,Property,interval] |timeout |How long to wait before declaring the action has failed. indexterm:[timeout,Action Property] indexterm:[Action,Property,timeout] |on-fail |The action to take if this action ever fails. Allowed values: * 'ignore' - Pretend the resource did not fail * 'block' - Don't perform any further operations on the resource * 'stop' - Stop the resource and do not start it elsewhere * 'restart' - Stop the resource and start it again (possibly on a different node) * 'fence' - STONITH the node on which the resource failed * 'standby' - Move _all_ resources away from the node on which the resource failed The default for the +stop+ operation is +fence+ when STONITH is enabled and +block+ otherwise. All other operations default to +restart+. indexterm:[on-fail,Action Property] indexterm:[Action,Property,on-fail] |enabled |If +false+, the operation is treated as if it does not exist. Allowed values: +true+, +false+ indexterm:[enabled,Action Property] indexterm:[Action,Property,enabled] |record-pending |If +true+, the intention to perform the operation is recorded so that GUIs and CLI tools can indicate that an operation is in progress. This is best set as an 'operation default' (see next section). Allowed values: +true+, +false+. indexterm:[enabled,Action Property] indexterm:[Action,Property,enabled] |========================================================= [[s-operation-defaults]] === Setting Global Defaults for Operations === To set a default value for a operation option, simply add it to the +op_defaults+ section with `crm_attribute`. Thus, -[source,C] +---- # crm_attribute --type op_defaults --attr-name timeout --attr-value 20s +---- would default each operation's +timeout+ to 20 seconds. If an operation's definition also includes a value for +timeout+, then that value would be used instead (for that operation only). ==== When Resources Take a Long Time to Start/Stop ==== There are a number of implicit operations that the cluster will always perform - +start+, +stop+ and a non-recurring +monitor+ operation (used at startup to check the resource isn't already active). If one of these is taking too long, then you can create an entry for them and simply specify a new value. .An OCF resource with custom timeouts for its implicit actions ===== [source,XML] ------- ------- ===== ==== Multiple Monitor Operations ==== Provided no two operations (for a single resource) have the same name and interval you can have as many monitor operations as you like. In this way you can do a superficial health check every minute and progressively more intense ones at higher intervals. To tell the resource agent what kind of check to perform, you need to provide each monitor with a different value for a common parameter. The OCF standard creates a special parameter called +OCF_CHECK_LEVEL+ for this purpose and dictates that it is _"made available to the resource agent without the normal +OCF_RESKEY+ prefix"_. Whatever name you choose, you can specify it by adding an +instance_attributes+ block to the op tag. Note that it is up to each resource agent to look for the parameter and decide how to use it. .An OCF resource with two recurring health checks, performing different levels of checks - specified via +OCF_CHECK_LEVEL+. ===== [source,XML] ------- ------- ===== ==== Disabling a Monitor Operation ==== The easiest way to stop a recurring monitor is to just delete it. However, there can be times when you only want to disable it temporarily. In such cases, simply add +enabled="false"+ to the operation's definition. .Example of an OCF resource with a disabled health check ===== [source,XML] ------- ------- ===== This can be achieved from the command-line by executing -[source,C] +---- # cibadmin -M -X '' +---- Once you've done whatever you needed to do, you can then re-enable it with diff --git a/doc/Pacemaker_Explained/en-US/Ch-Stonith.txt b/doc/Pacemaker_Explained/en-US/Ch-Stonith.txt index fae0fe5c54..b27524c646 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Stonith.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Stonith.txt @@ -1,741 +1,739 @@ = Configure STONITH = //// We prefer [[ch-stonith]], but older versions of asciidoc dont deal well with that construct for chapter headings //// anchor:ch-stonith[Chapter 13, STONITH] indexterm:[STONITH, Configuration] == What Is STONITH == STONITH is an acronym for Shoot-The-Other-Node-In-The-Head and it protects your data from being corrupted by rogue nodes or concurrent access. Just because a node is unresponsive, this doesn't mean it isn't accessing your data. The only way to be 100% sure that your data is safe, is to use STONITH so we can be certain that the node is truly offline, before allowing the data to be accessed from another node. STONITH also has a role to play in the event that a clustered service cannot be stopped. In this case, the cluster uses STONITH to force the whole node offline, thereby making it safe to start the service elsewhere. == What STONITH Device Should You Use == It is crucial that the STONITH device can allow the cluster to differentiate between a node failure and a network one. The biggest mistake people make in choosing a STONITH device is to use remote power switch (such as many on-board IMPI controllers) that shares power with the node it controls. In such cases, the cluster cannot be sure if the node is really offline, or active and suffering from a network fault. Likewise, any device that relies on the machine being active (such as SSH-based "devices" used during testing) are inappropriate. == Differences of STONITH Resources == Stonith resources are somewhat special in Pacemaker. In previous versions, only "running" resources could be used by Pacemaker for fencing. This requirement has been relaxed to allow other parts of the cluster (such as resources like DRBD) to reliably initiate fencing. footnote:[Fencing a node while Pacemaker was moving stonith resources around would otherwise fail] Now all nodes have access to their definitions and instantiate them on-the-fly when needed, however preference is given to 'verified' instances which are the ones the cluster has explicitly started. In the case of a cluster split, the partition with a verified instance will have a slight advantage as stonith-ng in the other partition will have to hear from all its current peers before choosing a node to perform the fencing. [NOTE] =========== To disable a fencing device/resource, 'target-role' can be set as you would for a normal resource. =========== [NOTE] =========== To prevent a specific node from using a fencing device, location constraints will work as expected. =========== [IMPORTANT] =========== Currently there is a limitation that fencing resources may only have a one set of meta-attributes and one set of instance-attributes. This can be revisited if it becomes a significant limitation for people. =========== .Properties of Fencing Devices [width="95%",cols="1m,1m,1m,5<",options="header",align="center"] |========================================================= |Field |Type |Default |Description |stonith-timeout |time |60s |How long to wait for the STONITH action to complete per a stonith device. Overrides the stonith-timeout cluster property indexterm:[stonith-timeout,Fencing] indexterm:[Fencing,Property,stonith-timeout] |priority |integer |0 |The priority of the stonith resource. Devices are tried in order of highest priority to lowest. indexterm:[priority,Fencing] indexterm:[Fencing,Property,priority] |pcmk_host_argument |string |port |Advanced use only: An alternate parameter to supply instead of 'port' Some devices do not support the standard 'port' parameter or may provide additional ones. Use this to specify an alternate, device-specific, parameter that should indicate the machine to be fenced. A value of 'none' can be used to tell the cluster not to supply any additional parameters. indexterm:[pcmk_host_argument,Fencing] indexterm:[Fencing,Property,pcmk_host_argument] |pcmk_host_map |string | |A mapping of host names to ports numbers for devices that do not support host names. Eg. node1:1;node2:2,3 would tell the cluster to use port 1 for node1 and ports 2 and 3 for node2 indexterm:[pcmk_host_map,Fencing] indexterm:[Fencing,Property,pcmk_host_map] |pcmk_host_list |string | |A list of machines controlled by this device (Optional unless pcmk_host_check=static-list). indexterm:[pcmk_host_list,Fencing] indexterm:[Fencing,Property,pcmk_host_list] |pcmk_host_check |string |dynamic-list |How to determin which machines are controlled by the device. Allowed values: dynamic-list (query the device), static-list (check the pcmk_host_list attribute), none (assume every device can fence every machine) indexterm:[pcmk_host_check,Fencing] indexterm:[Fencing,Property,pcmk_host_check] |pcmk_reboot_action |string |reboot |Advanced use only: An alternate command to run instead of 'reboot' Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific, command that implements the 'reboot' action. indexterm:[pcmk_reboot_action,Fencing] indexterm:[Fencing,Property,pcmk_reboot_action] |pcmk_reboot_timeout |time |60s |Advanced use only: Specify an alternate timeout to use for reboot actions instead of stonith-timeout Some devices need much more/less time to complete than normal. Use this to specify an alternate, device-specific, timeout for 'reboot' actions. indexterm:[pcmk_reboot_timeout,Fencing] indexterm:[Fencing,Property,pcmk_reboot_timeout] |pcmk_reboot_retries |integer |2 |Advanced use only: The maximum number of times to retry the 'reboot' command within the timeout period Some devices do not support multiple connections. Operations may 'fail' if the device is busy with another task so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries 'reboot' actions before giving up. indexterm:[pcmk_reboot_retries,Fencing] indexterm:[Fencing,Property,pcmk_reboot_retries] |pcmk_off_action |string |off |Advanced use only: An alternate command to run instead of 'off' Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific, command that implements the 'off' action. indexterm:[pcmk_off_action,Fencing] indexterm:[Fencing,Property,pcmk_off_action] |pcmk_off_timeout |time |60s |Advanced use only: Specify an alternate timeout to use for off actions instead of stonith-timeout Some devices need much more/less time to complete than normal. Use this to specify an alternate, device-specific, timeout for 'off' actions. indexterm:[pcmk_off_timeout,Fencing] indexterm:[Fencing,Property,pcmk_off_timeout] |pcmk_off_retries |integer |2 |Advanced use only: The maximum number of times to retry the 'off' command within the timeout period Some devices do not support multiple connections. Operations may 'fail' if the device is busy with another task so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries 'off' actions before giving up. indexterm:[pcmk_off_retries,Fencing] indexterm:[Fencing,Property,pcmk_off_retries] |pcmk_list_action |string |list |Advanced use only: An alternate command to run instead of 'list' Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific, command that implements the 'list' action. indexterm:[pcmk_list_action,Fencing] indexterm:[Fencing,Property,pcmk_list_action] |pcmk_list_timeout |time |60s |Advanced use only: Specify an alternate timeout to use for list actions instead of stonith-timeout Some devices need much more/less time to complete than normal. Use this to specify an alternate, device-specific, timeout for 'list' actions. indexterm:[pcmk_list_timeout,Fencing] indexterm:[Fencing,Property,pcmk_list_timeout] |pcmk_list_retries |integer |2 |Advanced use only: The maximum number of times to retry the 'list' command within the timeout period Some devices do not support multiple connections. Operations may 'fail' if the device is busy with another task so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries 'list' actions before giving up. indexterm:[pcmk_list_retries,Fencing] indexterm:[Fencing,Property,pcmk_list_retries] |pcmk_monitor_action |string |monitor |Advanced use only: An alternate command to run instead of 'monitor' Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific, command that implements the 'monitor' action. indexterm:[pcmk_monitor_action,Fencing] indexterm:[Fencing,Property,pcmk_monitor_action] |pcmk_monitor_timeout |time |60s |Advanced use only: Specify an alternate timeout to use for monitor actions instead of stonith-timeout Some devices need much more/less time to complete than normal. Use this to specify an alternate, device-specific, timeout for 'monitor' actions. indexterm:[pcmk_monitor_timeout,Fencing] indexterm:[Fencing,Property,pcmk_monitor_timeout] |pcmk_monitor_retries |integer |2 |Advanced use only: The maximum number of times to retry the 'monitor' command within the timeout period Some devices do not support multiple connections. Operations may 'fail' if the device is busy with another task so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries 'monitor' actions before giving up. indexterm:[pcmk_monitor_retries,Fencing] indexterm:[Fencing,Property,pcmk_monitor_retries] |pcmk_status_action |string |status |Advanced use only: An alternate command to run instead of 'status' Some devices do not support the standard commands or may provide additional ones. Use this to specify an alternate, device-specific, command that implements the 'status' action. indexterm:[pcmk_status_action,Fencing] indexterm:[Fencing,Property,pcmk_status_action] |pcmk_status_timeout |time |60s |Advanced use only: Specify an alternate timeout to use for status actions instead of stonith-timeout Some devices need much more/less time to complete than normal. Use this to specify an alternate, device-specific, timeout for 'status' actions. indexterm:[pcmk_status_timeout,Fencing] indexterm:[Fencing,Property,pcmk_status_timeout] |pcmk_status_retries |integer |2 |Advanced use only: The maximum number of times to retry the 'status' command within the timeout period Some devices do not support multiple connections. Operations may 'fail' if the device is busy with another task so Pacemaker will automatically retry the operation, if there is time remaining. Use this option to alter the number of times Pacemaker retries 'status' actions before giving up. indexterm:[pcmk_status_retries,Fencing] indexterm:[Fencing,Property,pcmk_status_retries] |========================================================= == Configuring STONITH == [NOTE] =========== Both configuration shells include functionality to simplify the process below, particularly the step for deciding which parameters are required. However since this document deals only with core components, you should refer to the Stonith chapter of +Clusters from Scratch+ for those details. =========== . Find the correct driver: +stonith_admin --list-installed+ . Find the required parameters associated with the device: +stonith_admin --metadata --agent + . Create a file called +stonith.xml+ containing a primitive resource with a class of 'stonith', a type of and a parameter for each of the values returned in step 2. . If the device does not know how to fence nodes based on their uname, you may also need to set the special +pcmk_host_map+ parameter. See +man stonithd+ for details. . If the device does not support the list command, you may also need to set the special +pcmk_host_list+ and/or +pcmk_host_check+ parameters. See +man stonithd+ for details. . If the device does not expect the victim to be specified with the port parameter, you may also need to set the special +pcmk_host_argument+ parameter. See +man stonithd+ for details. . Upload it into the CIB using cibadmin: +cibadmin -C -o resources --xml-file stonith.xml+ . Set stonith-enabled to true. +crm_attribute -t crm_config -n stonith-enabled -v true+ . Once the stonith resource is running, you can test it by executing: +stonith_admin --reboot nodename+. Although you might want to stop the cluster on that machine first. === Example === Assuming we have an chassis containing four nodes and an IPMI device active on 10.0.0.1, then we would chose the fence_ipmilan driver in step 2 and obtain the following list of parameters .Obtaining a list of STONITH Parameters -[source,C] ---- # stonith_admin --metadata -a fence_ipmilan ---- [source,XML] ---- fence_ipmilan is an I/O Fencing agent which can be used with machines controlled by IPMI. This agent calls support software using ipmitool (http://ipmitool.sf.net/). To use fence_ipmilan with HP iLO 3 you have to enable lanplus option (lanplus / -P) and increase wait after operation to 4 seconds (power_wait=4 / -T 4) IPMI Lan Auth type (md5, password, or none) IPMI Lan IP to talk to Password (if required) to control power on IPMI device Script to retrieve password (if required) Use Lanplus Username/Login (if required) to control power on IPMI device Operation to perform. Valid operations: on, off, reboot, status, list, diag, monitor or metadata Timeout (sec) for IPMI operation Ciphersuite to use (same as ipmitool -C parameter) Method to fence (onoff or cycle) Wait X seconds after on/off operation Wait X seconds before fencing is started Verbose mode ---- from which we would create a STONITH resource fragment that might look like this: .Sample STONITH Resource [source,XML] ---- ---- And finally, since we disabled it earlier, we need to re-enable STONITH. -[source,Bash] ---- # crm_attribute -t crm_config -n stonith-enabled -v true ---- == Advanced Fencing Configurations == Some people consider that having one fencing device is a single point of failure footnote:[Not true, since a node or resource must fail before fencing even has a chance to], others prefer removing the node from the storage and network instead of turning it off. Whatever the reason, Pacemaker supports fencing nodes with multiple devices through a feature called fencing topologies. Simply create the individual devices as you normally would and then define one or more fencing levels in the fencing-topology section in the configuration. * Each level is attempted in +ascending index+ order * If a device fails, +processing terminates+ for the current level. No further devices in that level are exercised and the next level is attempted instead. * If the operation succeeds for all the listed devices in a level, the level is deemed to have passed * The operation is finished +when a level has passed+ (success), or all levels have been attempted (failed) * If the operation failed, the next step is determined by the Policy Engine and/or crmd. Some possible uses of topologies include: * try poison-pill and fail back to power * try disk and network, and fall back to power if either fails * initiate a kdump and then poweroff the node .Properties of Fencing Levels [width="95%",cols="1m,6<",options="header",align="center"] |========================================================= |Field |Description |id |Your name for the level indexterm:[id,fencing-level] indexterm:[Fencing,fencing-level,id] |target |The node to which this level applies indexterm:[target,fencing-level] indexterm:[Fencing,fencing-level,target] |index |The order in which to attempt the levels. Levels are attempted in +ascending index+ order +until one succeeds+. indexterm:[index,fencing-level] indexterm:[Fencing,fencing-level,index] |devices |A comma separated list of devices for which the indexterm:[devices,fencing-level] indexterm:[Fencing,fencing-level,devices] |========================================================= === Example use of Fencing Topologies === [source,XML] ---- ... ... ---- === Example use of advanced Fencing Topologies: dual layer and dual devices === The following example illustrates an advanced use of +fencing_topology+ in a cluster with the following properties: * 3 nodes (2 active prod-mysql nodes, 1 prod_mysql-rep in standby for quorum purposes) * the active nodes have an IPMI-controlled power board reached at 10.10.10.1 and 10.10.10.2 * the active nodes also have two independant PSUs (Power Supplu Units) connected to two independant PDUs (Power Distribution Unit) reached at 10.20.1.1 (port 10 and port 11) and 10.20.2.1 (port 10 and port 11) * the first fencing method uses the +fence_ipmi+ agent * the second fencing method uses the +fence_apc_snmp+ agent targetting 2 fencing devices (one per PSU, either port 10 or 11) * fencing is only implemented for the active nodes and has location constraints * fencing topology is set to try IPMI fencing first then default to a "sure-kill" dual PDU fencing In a normal failure scenario, STONITH will first select +fence_ipmi+ to try and kill the faulty node. Using a +fencing_topology+, if that first method fails, STONITH will then move on to selecting +fence_apc_snmp+ twice: * once for the first PDU * again for the second PDU The fence action is considered successful only if both PDUs report the required status. If any of them fails, STONITH loops back to the first fencing method, +fence_ipmi+, and so on until the node is fenced or fencing action is cancelled. .First fencing method: single IPMI device Each cluster node has it own dedicated IPMI channel that can be called for fencing using the following primitives: [source,XML] ---- ---- .Second fencing method: dual PDU devices Each cluster node also has two distinct power channels controlled by two distinct PDUs. That means a total of 4 fencing devices configured as follows: - Node 1, PDU 1, PSU 1 @ port 10 - Node 1, PDU 2, PSU 2 @ port 10 - Node 2, PDU 1, PSU 1 @ port 11 - Node 2, PDU 2, PSU 2 @ port 11 The matching fencing agents are configured as follows: [source,XML] ---- ---- .Location Constraints To prevent STONITH from running a fencing agent on the very same node it is supposed to fence, constraints are placed on all the fencing primitives: [source,XML] ---- ---- .Fencing topology Now that all the fencing resources are defined, it's time to create the right topology. We want to first fence using IPMI and if that does not work, fence both PDUs to effectively and surely kill the node. [source,XML] ---- ---- Please note, in +fencing_topology+, the lower index value determines the priority of the first fencing method. .Final configuration Put together, the configuration looks like this: [source,XML] ---- ... ... ---- diff --git a/doc/Pacemaker_Explained/en-US/Ch-Utilization.txt b/doc/Pacemaker_Explained/en-US/Ch-Utilization.txt index 6eeb063a8a..99b1fe8776 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Utilization.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Utilization.txt @@ -1,221 +1,222 @@ = Utilization and Placement Strategy = == Background == Pacemaker decides where to place a resource according to the resource allocation scores on every node. The resource will be allocated to the node where the resource has the highest score. If the resource allocation scores on all the nodes are equal, by the `default` placement strategy, Pacemaker will choose a node with the least number of allocated resources for balancing the load. If the number of resources on each node is equal, the first eligible node listed in cib will be chosen to run the resource. Though resources are different. They may consume different amounts of the capacities of the nodes. Actually, we cannot ideally balance the load just according to the number of resources allocated to a node. Besides, if resources are placed such that their combined requirements exceed the provided capacity, they may fail to start completely or run with degraded performance. To take these into account, Pacemaker allows you to specify the following configurations: . The `capacity` a certain `node provides`. . The `capacity` a certain `resource requires`. . An overall `strategy` for placement of resources. == Utilization attributes == To configure the capacity a node provides and the resource's requirements, use `utilization` attributes. You can name the `utilization` attributes according to your preferences and define as many `name/value` pairs as your configuration needs. However, the attribute's values must be `integers`. First, specify the capacities the nodes provide: [source,XML] ---- ---- Then, specify the capacities the resources require: [source,XML] ---- ---- A node is considered eligible for a resource if it has sufficient free capacity to satisfy the resource's requirements. The nature of the required or provided capacities is completely irrelevant for Pacemaker, it just makes sure that all capacity requirements of a resource are satisfied before placing a resource to a node. == Placement Strategy == After you have configured the capacities your nodes provide and the capacities your resources require, you need to set the `placement-strategy` in the global cluster options, otherwise the capacity configurations have `no effect`. Four values are available for the `placement-strategy`: `default`:: Utilization values are not taken into account at all, per default. Resources are allocated according to allocation scores. If scores are equal, resources are evenly distributed across nodes. `utilization`:: Utilization values are taken into account when deciding whether a node is considered eligible if it has sufficient free capacity to satisfy the resource's requirements. However, load-balancing is still done based on the number of resources allocated to a node. `balanced`:: Utilization values are taken into account when deciding whether a node is eligible to serve a resource; an attempt is made to spread the resources evenly, optimizing resource performance. `minimal`:: Utilization values are taken into account when deciding whether a node is eligible to serve a resource; an attempt is made to concentrate the resources on as few nodes as possible, thereby enabling possible power savings on the remaining nodes. Set `placement-strategy` with `crm_attribute`: -[source,C] +---- # crm_attribute --attr-name placement-strategy --attr-value balanced +---- Now Pacemaker will ensure the load from your resources will be distributed evenly throughout the cluster - without the need for convoluted sets of colocation constraints. == Allocation Details == === Which node is preferred to be chosen to get consumed first on allocating resources? === - The node that is most healthy (which has the highest node weight) gets consumed first. - If their weights are equal: * If `placement-strategy="default|utilization"`, the node that has the least number of allocated resources gets consumed first. ** If their numbers of allocated resources are equal, the first eligible node listed in cib gets consumed first. * If `placement-strategy="balanced"`, the node that has more free capacity gets consumed first. ** If the free capacities of the nodes are equal, the node that has the least number of allocated resources gets consumed first. *** If their numbers of allocated resources are equal, the first eligible node listed in cib gets consumed first. * If `placement-strategy="minimal"`, the first eligible node listed in cib gets consumed first. ==== Which node has more free capacity? ==== This will be quite clear if we only define one type of `capacity`. While if we define multiple types of `capacity`, for example: - If `nodeA` has more free `cpus`, `nodeB` has more free `memory`, their free capacities are equal. - If `nodeA` has more free `cpus`, while `nodeB` has more free `memory` and `storage`, `nodeB` has more free capacity. === Which resource is preferred to be chosen to get assigned first? === - The resource that has the highest priority gets allocated first. - If their priorities are equal, check if they are already running. The resource that has the highest score on the node where it's running gets allocated first (to prevent resource shuffling). - If the scores above are equal or they are not running, the resource has the highest score on the preferred node gets allocated first. - If the scores above are equal, the first runnable resource listed in cib gets allocated first. == Limitations == This type of problem Pacemaker is dealing with here is known as the http://en.wikipedia.org/wiki/Knapsack_problem[knapsack problem] and falls into the http://en.wikipedia.org/wiki/NP-complete[NP-complete] category of computer science problems - which is fancy way of saying "it takes a really long time to solve". Clearly in a HA cluster, it's not acceptable to spend minutes, let alone hours or days, finding an optional solution while services remain unavailable. So instead of trying to solve the problem completely, Pacemaker uses a 'best effort' algorithm for determining which node should host a particular service. This means it arrives at a solution much faster than traditional linear programming algorithms, but by doing so at the price of leaving some services stopped. In the contrived example above: - `rsc-small` would be allocated to `node1` - `rsc-medium` would be allocated to `node2` - `rsc-large` would remain inactive Which is not ideal. == Strategies for Dealing with the Limitations == - Ensure you have sufficient physical capacity. It might sounds obvious, but if the physical capacity of your nodes is (close to) maxed out by the cluster under normal conditions, then failover isn't going to go well. Even without the Utilization feature, you'll start hitting timeouts and getting secondary failures'. - Build some buffer into the capabilities advertised by the nodes. Advertise slightly more resources than we physically have on the (usually valid) assumption that a resource will not use 100% of the configured number of cpu/memory/etc `all` the time. This practice is also known as 'over commit'. - Specify resource priorities. If the cluster is going to sacrifice services, it should be the ones you care (comparatively) about the least. Ensure that resource priorities are properly set so that your most important resources are scheduled first. diff --git a/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt b/doc/shared/en-US/pacemaker-intro.txt similarity index 85% copy from doc/Clusters_from_Scratch/en-US/Ch-Intro.txt copy to doc/shared/en-US/pacemaker-intro.txt index ca81b217f7..bf432fc26d 100644 --- a/doc/Clusters_from_Scratch/en-US/Ch-Intro.txt +++ b/doc/shared/en-US/pacemaker-intro.txt @@ -1,164 +1,141 @@ -= Read-Me-First = - -== The Scope of this Document == - -Computer clusters can be used to provide highly available services or -resources. The redundancy of multiple machines is used to guard -against failures of many types. - -This document will walk through the installation and setup of simple -clusters using the &DISTRO; distribution, version &DISTRO_VERSION;. - -The clusters described here will use Pacemaker and Corosync to provide -resource management and messaging. Required packages and modifications -to their configuration files are described along with the use of the -Pacemaker command line tool for generating the XML used for cluster -control. - -Pacemaker is a central component and provides the resource management -required in these systems. This management includes detecting and -recovering from the failure of various nodes, resources and services -under its control. - -When more in depth information is required and for real world usage, -please refer to the http://www.clusterlabs.org/doc/[Pacemaker Explained] manual. == What Is Pacemaker? == Pacemaker is a cluster resource manager. It achieves maximum availability for your cluster services (aka. resources) by detecting and recovering from node- and resource-level failures by making use of the messaging and membership capabilities provided by your preferred cluster infrastructure (either http://www.corosync.org/[Corosync] or http://linux-ha.org/wiki/Heartbeat[Heartbeat]). Pacemaker's key features include: * Detection and recovery of node and service-level failures * Storage agnostic, no requirement for shared storage * Resource agnostic, anything that can be scripted can be clustered * Supports fencing (aka. STONITH) for ensuring data integrity * Supports large and small clusters * Supports both quorate and resource-driven clusters * Supports practically any redundancy configuration * Automatically replicated configuration that can be updated from any node * Ability to specify cluster-wide service ordering, colocation and anti-colocation * Support for advanced service types ** Clones: for services which need to be active on multiple nodes ** Multi-state: for services with multiple modes (eg. master/slave, primary/secondary) * Unified, scriptable, cluster management tools. == Pacemaker Architecture == At the highest level, the cluster is made up of three pieces: * Non-cluster-aware components. These pieces include the resources themselves; scripts that start, stop and monitor them; and a local daemon that masks the differences between the different standards these scripts implement. * Resource management. Pacemaker provides the brain that processes and reacts to events regarding the cluster. These events include nodes joining or leaving the cluster; resource events caused by failures, maintenance and scheduled activities; and other administrative actions. Pacemaker will compute the ideal state of the cluster and plot a path to achieve it after any of these events. This may include moving resources, stopping nodes and even forcing them offline with remote power switches. * Low-level infrastructure. Projects like Corosync, CMAN and Heartbeat provide reliable messaging, membership and quorum information about the cluster. When combined with Corosync, Pacemaker also supports popular open source cluster filesystems. footnote:[Even though Pacemaker also supports Heartbeat, the filesystems need to use the stack for messaging and membership, and Corosync seems to be what they're standardizing on. Technically, it would be possible for them to support Heartbeat as well, but there seems little interest in this.] Due to past standardization within the cluster filesystem community, cluster filesystems make use of a common distributed lock manager, which makes use of Corosync for its messaging and membership capabilities (which nodes are up/down) and Pacemaker for fencing services. .The Pacemaker Stack image::images/pcmk-stack.png["The Pacemaker stack",width="10cm",height="7.5cm",align="center"] === Internal Components === Pacemaker itself is composed of five key components: * Cluster Information Base (CIB) * Cluster Resource Management daemon (CRMd) * Local Resource Management daemon (LRMd) * Policy Engine (PEngine or PE) * Fencing daemon (STONITHd) .Internal Components image::images/pcmk-internals.png["Subsystems of a Pacemaker cluster",align="center",scaledwidth="65%"] The CIB uses XML to represent both the cluster's configuration and current state of all resources in the cluster. The contents of the CIB are automatically kept in sync across the entire cluster and are used by the PEngine to compute the ideal state of the cluster and how it should be achieved. This list of instructions is then fed to the Designated Controller (DC). Pacemaker centralizes all cluster decision making by electing one of the CRMd instances to act as a master. Should the elected CRMd process (or the node it is on) fail, a new one is quickly established. The DC carries out the PEngine's instructions in the required order by passing them to either the Local Resource Management daemon (LRMd) or CRMd peers on other nodes via the cluster messaging infrastructure (which in turn passes them on to their LRMd process). The peer nodes all report the results of their operations back to the DC and, based on the expected and actual results, will either execute any actions that needed to wait for the previous one to complete, or abort processing and ask the PEngine to recalculate the ideal cluster state based on the unexpected results. In some cases, it may be necessary to power off nodes in order to protect shared data or complete resource recovery. For this, Pacemaker comes with STONITHd. STONITH is an acronym for Shoot-The-Other-Node-In-The-Head and is usually implemented with a remote power switch. In Pacemaker, STONITH devices are modeled as resources (and configured in the CIB) to enable them to be easily monitored for failure, however STONITHd takes care of understanding the STONITH topology such that its clients simply request a node be fenced, and it does the rest. == Types of Pacemaker Clusters == Pacemaker makes no assumptions about your environment. This allows it to support practically any http://en.wikipedia.org/wiki/High-availability_cluster#Node_configurations[redundancy configuration] including Active/Active, Active/Passive, N+1, N+M, N-to-1 and N-to-N. .Active/Passive Redundancy image::images/pcmk-active-passive.png["Active/Passive Redundancy",width="10cm",height="7.5cm",align="center"] Two-node Active/Passive clusters using Pacemaker and DRBD are a cost-effective solution for many High Availability situations. .Shared Failover image::images/pcmk-shared-failover.png["Shared Failover",width="10cm",height="7.5cm",align="center"] By supporting many nodes, Pacemaker can dramatically reduce hardware costs by allowing several active/passive clusters to be combined and share a common backup node .N to N Redundancy image::images/pcmk-active-active.png["N to N Redundancy",width="10cm",height="7.5cm",align="center"] When shared storage is available, every node can potentially be used for failover. Pacemaker can even run multiple copies of services to spread out the workload. +