diff --git a/doc/Pacemaker_Explained/en-US/Author_Group.xml b/doc/Pacemaker_Explained/en-US/Author_Group.xml index 7f3c297cee..08fc1f72ed 100644 --- a/doc/Pacemaker_Explained/en-US/Author_Group.xml +++ b/doc/Pacemaker_Explained/en-US/Author_Group.xml @@ -1,53 +1,59 @@ AndrewBeekhof Red Hat Primary author andrew@beekhof.net + + KenGaillot + Red Hat + Co-author + kgaillot@redhat.com + PhilippMarek LINBit Style and formatting updates. Indexing. philipp.marek@linbit.com TanjaRoth SUSE Utilization chapter Resource Templates chapter Multi-Site Clusters chapter taroth@suse.com LarsMarowsky-Bree SUSE Multi-Site Clusters chapter lmb@suse.com YanGao SUSE Utilization chapter Resource Templates chapter Multi-Site Clusters chapter ygao@suse.com ThomasSchraitle SUSE Utilization chapter Resource Templates chapter Multi-Site Clusters chapter toms@suse.com DejanMuhamedagic SUSE Resource Templates chapter dmuhamedagic@suse.com diff --git a/doc/Pacemaker_Explained/en-US/Book_Info.xml b/doc/Pacemaker_Explained/en-US/Book_Info.xml index da196e34ae..3da61de4f7 100644 --- a/doc/Pacemaker_Explained/en-US/Book_Info.xml +++ b/doc/Pacemaker_Explained/en-US/Book_Info.xml @@ -1,35 +1,35 @@ Configuration Explained An A-Z guide to Pacemaker's Configuration Options Pacemaker 2.0 - 11 + 12 0 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 Pacemaker's Cluster Information Base (CIB). diff --git a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt index d0aba3914f..dd74e59735 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt @@ -1,729 +1,732 @@ :compat-mode: legacy = Advanced Configuration = [[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 in the middle of the business day -- hardly desirable. To specify a date and 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, its 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 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] ===== [[s-failure-handling]] == Handling Resource Failure == By default, Pacemaker will attempt to recover failed resources by restarting them. However, failure recovery is highly configurable. === Failure Counts === Pacemaker tracks resource failures for each combination of node, resource, and operation (start, stop, monitor, etc.). You can query the fail count for a particular node, resource, and/or operation using the `crm_failcount` command. For example, to see how many times the 10-second monitor for +myrsc+ has failed on +node1+, run: ---- # crm_failcount --query -r myrsc -N node1 -n monitor -I 10s ---- If you omit the node, `crm_failcount` will use the local node. If you omit the operation and interval, `crm_failcount` will display the sum of the fail counts for all operations on the resource. You can use `crm_resource --cleanup` or `crm_failcount --delete` to clear fail counts. For example, to clear the above monitor failures, run: ---- # crm_resource --cleanup -r myrsc -N node1 -n monitor -I 10s ---- If you omit the resource, `crm_resource --cleanup` will clear failures for all resources. If you omit the node, it will clear failures on all nodes. If you omit the operation and interval, it will clear the failures for all operations on the resource. [NOTE] ==== Even when cleaning up only a single operation, all failed operations will disappear from the status display. This allows us to trigger a re-check of the resource's current status. ==== Higher-level tools may provide other commands for querying and clearing fail counts. The `crm_mon` tool shows the current cluster status, including any failed operations. To see the current fail counts for any failed resources, call `crm_mon` with the `--failcounts` option. This shows the fail counts per resource (that is, the sum of any operation fail counts for the resource). === Failure Response === Normally, if a running resource fails, pacemaker will try to stop it and start it again. Pacemaker will choose the best location to start it each time, which may be the same node that it failed on. However, if a resource fails repeatedly, it is possible that there is an underlying problem on that node, and you might desire trying a different node in such a case. Pacemaker allows you to set your preference via the +migration-threshold+ resource meta-attribute. footnote:[ The naming of this option was perhaps unfortunate as it is easily confused with live 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. ] If you define +migration-threshold=pass:[N]+ for a resource, it will be banned from the original node after 'N' failures. [NOTE] ==== The +migration-threshold+ is per 'resource', even though fail counts are tracked per 'operation'. The operation fail counts are added together to compare against the +migration-threshold+. ==== By default, fail counts remain until manually cleared by an administrator using `crm_resource --cleanup` or `crm_failcount --delete` (hopefully after first fixing the failure's cause). It is possible to have fail counts expire automatically by setting the +failure-timeout+ resource meta-attribute. [IMPORTANT] ==== A successful operation does not clear past failures. If a recurring monitor operation fails once, succeeds many times, then fails again days later, its fail count is 2. Fail counts are cleared only by manual intervention or falure timeout. ==== For example, 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 stickiness and constraint scores) after one minute. [NOTE] ==== +failure-timeout+ is measured since the most recent failure. That is, older failures do not individually time out and lower the fail count. Instead, all failures are timed out simultaneously (and the fail count is reset to 0) if there is no new failure for the timeout period. ==== There are two exceptions to the migration threshold concept: when a resource either fails to start or fails to stop. If the cluster property +start-failure-is-fatal+ is set to +true+ (which is the default), start failures cause the fail count 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 <> to understand how timeouts work before configuring a +failure-timeout+. == Moving Resources == indexterm:[Moving,Resources] indexterm:[Resource,Moving] === Moving Resources Manually === There are primarily two occasions when you would want to move a resource from its current location: when the whole node is under maintenance, and when a single resource needs to be moved. ==== Standby Mode ==== Since everything eventually comes down to a score, you could create constraints for every resource to prevent them from running on one node. While pacemaker 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, run: ---- # crm_standby -G ---- A value of +on+ indicates that the node is _not_ able to host any resources, while a value of +off+ says that it _can_. You can also check the status of other nodes in the cluster by specifying the `--node` option: ---- # crm_standby -G --node sles-2 ---- To change the current node's standby status, use `-v` instead of `-G`: ---- # crm_standby -v on ---- Again, you can change another host's value by supplying a hostname with `--node`. +A cluster node in standby mode will not run resources, but still contributes to +quorum, and may fence or be fenced by nodes. + ==== Moving One Resource ==== When only one resource is required to move, we could 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+ were running on +sles-1+ and you wanted it moved to a specific location, the command would look something like: ---- # 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 ---- # 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: ---- # 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`: ---- # 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: ---- # crm_resource -B -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 creating both positive and negative constraints. E.g. +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. === Moving Resources Due to Connectivity Changes === You can configure the cluster to move resources when external connectivity is lost in two steps. ==== Tell Pacemaker to Monitor Connectivity ==== First, add an *ocf:pacemaker:ping* resource to the cluster. The *ping* resource uses the system utility of the same name to a test whether list of machines (specified by DNS hostname or IPv4/IPv6 address) are reachable and uses the results to maintain a node attribute called +pingd+ by default. footnote:[ The attribute name is customizable, in order to allow multiple ping groups to be defined. ] [NOTE] =========== Older versions of Pacemaker used a different agent *ocf:pacemaker:pingd* which is now deprecated in favor of *ping*. If your version of Pacemaker does not contain the *ping* resource agent, download the latest version from https://github.com/ClusterLabs/pacemaker/tree/master/extra/resources/ping =========== Normally, the ping resource should 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 ==== [IMPORTANT] ====== Before attempting the following, make sure you understand <>. ====== There are a number of ways to use the connectivity data. The most common setup is for people to have a single ping target (e.g. the service network's default gateway), to prevent the cluster from running a resource on any unconnected node. .Don't run a resource on unconnected nodes ===== [source,XML] ------- ------- ===== A more complex setup is to have a number of ping targets 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 targets. ===== [source,XML] ------- ... ... ... ------- ===== Alternatively, 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 five ping nodes but *sles-2* is only connected to two, then it would be as if you instead had the following constraints in your configuration: .How the cluster translates the above location 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] ------- ------- ===== [[s-migrating-resources]] === Migrating Resources === Normally, when the cluster needs to move a resource, it fully restarts the resource (i.e. stops the resource on the current node and starts it on the new node). However, some types of resources, such as Xen virtual guests, are able to move to another location without loss of state (often referred to as live migration or hot migration). In pacemaker, this is called resource migration. Pacemaker can be configured to migrate a resource when moving it, rather than restarting it. 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; and * 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 special 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 for a resource agent to implement migration, 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 agent must support +migrate_to+ and +migrate_from+ actions, and advertise them in its metadata. * The resource must have the +allow-migrate+ meta-attribute set to +true+ (which is not the default). If an otherwise migratable resource depends on another resource via an ordering constraint, there are special situations in which it will be restarted rather than migrated. For example, if the resource depends on a clone, and at the time the resource needs to be moved, the clone has instances that are stopping and instances that are starting, then the resource will be restarted. The scheduler is not yet able to model this situation correctly and so takes the safer (if less optimal) path. Also, if a migratable resource depends on a non-migratable resource, and both need to be moved, the migratable resource will be restarted. [[s-node-health]] == Tracking Node Health == A node may be functioning adequately as far as cluster membership is concerned, and yet be "unhealthy" in some respect that makes it an undesirable location for resources. For example, a disk drive may be reporting SMART errors, or the CPU may be highly loaded. Pacemaker offers a way to automatically move resources off unhealthy nodes. === Node Health Attributes === Pacemaker will treat any node attribute whose name starts with +#health+ as an indicator of node health. Node health attributes may have one of the following values: .Allowed Values for Node Health Attributes [width="95%",cols="1,<3",options="header",align="center"] |========================================================= |Value |Intended significance |+red+ |This indicator is unhealthy indexterm:[Node health,red] |+yellow+ |This indicator is becoming unhealthy indexterm:[Node health,yellow] |+green+ |This indicator is healthy indexterm:[Node health,green] |'integer' |A numeric score to apply to all resources on this node (0 or positive is healthy, negative is unhealthy) indexterm:[Node health,score] |========================================================= === Node Health Strategy === Pacemaker assigns a node health score to each node, as the sum of the values of all its node health attributes. This score will be used as a location constraint applied to this node for all resources. The +node-health-strategy+ cluster option controls how Pacemaker responds to changes in node health attributes, and how it translates +red+, +yellow+, and +green+ to scores. Allowed values are: .Node Health Strategies [width="95%",cols="1m,<3",options="header",align="center"] |========================================================= |Value |Effect |none |Do not track node health attributes at all. indexterm:[Node health,none] |migrate-on-red |Assign the value of +-INFINITY+ to +red+, and 0 to +yellow+ and +green+. This will cause all resources to move off the node if any attribute is +red+. indexterm:[Node health,migrate-on-red] |only-green |Assign the value of +-INFINITY+ to +red+ and +yellow+, and 0 to +green+. This will cause all resources to move off the node if any attribute is +red+ or +yellow+. indexterm:[Node health,only-green] |progressive |Assign the value of the +node-health-red+ cluster option to +red+, the value of +node-health-yellow+ to +yellow+, and the value of +node-health-green+ to +green+. Each node is additionally assigned a score of +node-health-base+ (this allows resources to start even if some attributes are +yellow+). This strategy gives the administrator finer control over how important each value is. indexterm:[Node health,progressive] |custom |Track node health attributes using the same values as +progressive+ for +red+, +yellow+, and +green+, but do not take them into account. The administrator is expected to implement a policy by defining rules (see <>) referencing node health attributes. indexterm:[Node health,custom] |========================================================= === Measuring Node Health === Since Pacemaker calculates node health based on node attributes, any method that sets node attributes may be used to measure node health. The most common ways are resource agents or separate daemons. Pacemaker provides examples that can be used directly or as a basis for custom code. The +ocf:pacemaker:HealthCPU+ and +ocf:pacemaker:HealthSMART+ resource agents set node health attributes based on CPU and disk parameters. The +ipmiservicelogd+ daemon sets node health attributes based on IPMI values (the +ocf:pacemaker:SystemHealth+ resource agent can be used to manage the daemon as a cluster resource). == Reloading Services After a Definition Change == The cluster automatically detects changes to the definition of services it manages. 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, the resource agent must: . Accept the +reload+ operation and perform any required actions. _The actions here depend completely on your application!_ + .The DRBD agent's logic for supporting +reload+ ===== [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 field changes. [NOTE] ====== Metadata will not be re-read unless the resource needs to be 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-Advanced-Resources.txt b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.txt index 9a358aed2f..339d2b7bd7 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.txt @@ -1,1455 +1,1468 @@ :compat-mode: legacy = Advanced Resource Types = [[group-resources]] == Groups - A Syntactic Shortcut == indexterm:[Group Resources] indexterm:[Resource,Groups] One of the most common elements of a cluster is a set of resources that need to be located together, start sequentially, and stop in the reverse order. To simplify this configuration, we support the concept of groups. .A group of two primitive resources ====== [source,XML] ------- ------- ====== Although the example above contains only two resources, there is no limit to the number of resources a group can contain. The example is also sufficient to explain the fundamental properties of a group: * Resources are started in the order they appear in (+Public-IP+ first, then +Email+) * Resources are stopped in the reverse order to which they appear in (+Email+ first, then +Public-IP+) If a resource in the group can't run anywhere, then nothing after that is allowed to run, too. * If +Public-IP+ can't run anywhere, neither can +Email+; * but if +Email+ can't run anywhere, this does not affect +Public-IP+ in any way The group above is logically equivalent to writing: .How the cluster sees a group resource ====== [source,XML] ------- ------- ====== Obviously as the group grows bigger, the reduced configuration effort can become significant. Another (typical) example of a group is a DRBD volume, the filesystem mount, an IP address, and an application that uses them. === Group Properties === .Properties of a Group Resource [width="95%",cols="3m,<5",options="header",align="center"] |========================================================= |Field |Description |id |A unique name for the group indexterm:[id,Group Resource Property] indexterm:[Resource,Group Property,id] |========================================================= === Group Options === Groups inherit the +priority+, +target-role+, and +is-managed+ properties from primitive resources. See <> for information about those properties. === Group Instance Attributes === Groups have no instance attributes. However, any that are set for the group object will be inherited by the group's children. === Group Contents === Groups may only contain a collection of cluster resources (see <>). To refer to a child of a group resource, just use the child's +id+ instead of the group's. === Group Constraints === Although it is possible to reference a group's children in constraints, it is usually preferable to reference the group itself. .Some constraints involving groups ====== [source,XML] ------- ------- ====== === Group Stickiness === indexterm:[resource-stickiness,Groups] Stickiness, the measure of how much a resource wants to stay where it is, is additive in groups. Every active resource of the group will contribute its stickiness value to the group's total. So if the default +resource-stickiness+ is 100, and a group has seven members, five of which are active, then the group as a whole will prefer its current location with a score of 500. [[s-resource-clone]] == Clones - Resources That Can Have Multiple Active Instances == indexterm:[Clone Resources] indexterm:[Resource,Clones] 'Clone' resources are resources that can have more than one copy active at the same time. This allows you, for example, to run a copy of a daemon on every node. You can clone any primitive or group resource. footnote:[ Of course, the service must support running multiple instances. ] === Anonymous versus Unique Clones === A clone resource is configured to be either 'anonymous' or 'globally unique'. Anonymous clones are the simplest. These behave completely identically everywhere they are running. Because of this, there can be only one instance of an anonymous clone active per node. The instances of globally unique clones are distinct entities. All instances are launched identically, but one instance of the clone is not identical to any other instance, whether running on the same node or a different node. As an example, a cloned IP address can use special kernel functionality such that each instance handles a subset of requests for the same IP address. [[s-resource-promotable]] === Promotable clones === indexterm:[Promotable Clone Resources] indexterm:[Resource,Promotable] If a clone is 'promotable', its instances can perform a special role that Pacemaker will manage via the +promote+ and +demote+ actions of the resource agent. Services that support such a special role have various terms for the special role and the default role: primary and secondary, master and replica, controller and worker, etc. Pacemaker uses the terms 'master' and 'slave', footnote:[ These are historical terms that will eventually be replaced, but the extensive use of them and the need for backward compatibility makes it a long process. You may see examples using a +master+ tag instead of a +clone+ tag with the +promotable+ meta-attribute set to +true+; the +master+ tag is supported, but deprecated, and will be removed in a future version. You may also see such services referred to as 'multi-state' or 'stateful'; these means the same thing as 'promotable'. ] but is agnostic to what the service calls them or what they do. All that Pacemaker cares about is that an instance comes up in the default role when started, and the resource agent supports the +promote+ and +demote+ actions to manage entering and exiting the special role. === Clone Properties === .Properties of a Clone Resource [width="95%",cols="3m,<5",options="header",align="center"] |========================================================= |Field |Description |id |A unique name for the clone indexterm:[id,Clone Property] indexterm:[Clone,Property,id] |========================================================= === Clone Options === <> inherited from primitive resources: +priority, target-role, is-managed+ .Clone-specific configuration options [width="95%",cols="1m,1,<3",options="header",align="center"] |========================================================= |Field |Default |Description |globally-unique |false |If +true+, each clone instance performs a distinct function indexterm:[globally-unique,Clone Option] indexterm:[Clone,Option,globally-unique] |clone-max |number of nodes in cluster |The maximum number of clone instances that can be started across the entire cluster indexterm:[clone-max,Clone Option] indexterm:[Clone,Option,clone-max] |clone-node-max |1 |If +globally-unique+ is +true+, the maximum number of clone instances that can be started on a single node indexterm:[clone-node-max,Clone Option] indexterm:[Clone,Option,clone-node-max] |clone-min |0 |Require at least this number of clone instances to be runnable before allowing resources depending on the clone to be runnable. A value of 0 means require all clone instances to be runnable. indexterm:[clone-min,Clone Option] indexterm:[Clone,Option,clone-min] |notify |false |Call the resource agent's +notify+ action for all active instances, before and after starting or stopping any clone instance. The resource agent must support this action. Allowed values: +false+, +true+ indexterm:[notify,Clone Option] indexterm:[Clone,Option,notify] |ordered |false |If +true+, clone instances must be started sequentially instead of in parallel Allowed values: +false+, +true+ indexterm:[ordered,Clone Option] indexterm:[Clone,Option,ordered] |interleave |false |When this clone is ordered relative to another clone, if this option is +false+ (the default), the ordering is relative to 'all' instances of the other clone, whereas if this option is +true+, the ordering is relative only to instances on the same node. Allowed values: +false+, +true+ indexterm:[interleave,Clone Option] indexterm:[Clone,Option,interleave] |promotable |false |If +true+, clone instances can perform a special role that Pacemaker will manage via the resource agent's +promote+ and +demote+ actions. The resource agent must support these actions. Allowed values: +false+, +true+ indexterm:[promotable,Clone Option] indexterm:[Clone,Option,promotable] |promoted-max |1 |If +promotable+ is +true+, the number of instances that can be promoted at one time across the entire cluster indexterm:[promoted-max,Clone Option] indexterm:[Clone,Option,promoted-max] |promoted-node-max |1 |If +promotable+ is +true+ and +globally-unique+ is +false+, the number of clone instances can be promoted at one time on a single node indexterm:[promoted-node-max,Clone Option] indexterm:[Clone,Option,promoted-node-max] |========================================================= For backward compatibility, +master-max+ and +master-node-max+ are accepted as aliases for +promoted-max+ and +promoted-node-max+, but are deprecated since 2.0.0, and support for them will be removed in a future version. === Clone Contents === Clones must contain exactly one primitive or group resource. .A clone that runs a web server on all nodes ==== [source,XML] ---- ---- ==== [WARNING] You should never reference the name of a clone's child (the primitive or group resource being cloned). If you think you need to do this, you probably need to re-evaluate your design. === Clone Instance Attributes === Clones have no instance attributes; however, any that are set here will be inherited by the clone's child. === Clone Constraints === In most cases, a clone will have a single instance on each active cluster node. If this is not the case, you can indicate which nodes the cluster should preferentially assign copies to with resource location constraints. These constraints are written no differently from those for primitive resources except that the clone's +id+ is used. .Some constraints involving clones ====== [source,XML] ------- ------- ====== Ordering constraints behave slightly differently for clones. In the example above, +apache-stats+ will wait until all copies of +apache-clone+ that need to be started have done so before being started itself. Only if _no_ copies can be started will +apache-stats+ be prevented from being active. Additionally, the clone will wait for +apache-stats+ to be stopped before stopping itself. Colocation of a primitive or group resource with a clone means that the resource can run on any node with an active instance of the clone. The cluster will choose an instance based on where the clone is running and the resource's own location preferences. Colocation between clones is also possible. If one clone +A+ is colocated with another clone +B+, the set of allowed locations for +A+ is limited to nodes on which +B+ is (or will be) active. Placement is then performed normally. ==== Promotable Clone Constraints ==== For promotable clone resources, the +first-action+ and/or +then-action+ fields for ordering constraints may be set to +promote+ or +demote+ to constrain the master role, and colocation constraints may contain +rsc-role+ and/or +with-rsc-role+ fields. .Additional colocation constraint options for promotable clone resources [width="95%",cols="1m,1,<3",options="header",align="center"] |========================================================= |Field |Default |Description |rsc-role |Started |An additional attribute of colocation constraints that specifies the role that +rsc+ must be in. Allowed values: +Started+, +Master+, +Slave+. indexterm:[rsc-role,Ordering Constraints] indexterm:[Constraints,Ordering,rsc-role] |with-rsc-role |Started |An additional attribute of colocation constraints that specifies the role that +with-rsc+ must be in. Allowed values: +Started+, +Master+, +Slave+. indexterm:[with-rsc-role,Ordering Constraints] indexterm:[Constraints,Ordering,with-rsc-role] |========================================================= .Constraints involving promotable clone resources ====== [source,XML] ------- ------- ====== In the example above, +myApp+ will wait until one of the database copies has been started and promoted to master before being started itself on the same node. Only if no copies can be promoted will +myApp+ be prevented from being active. Additionally, the cluster will wait for +myApp+ to be stopped before demoting the database. Colocation of a primitive or group resource with a promotable clone resource means that it can run on any node with an active instance of the promotable clone resource that has the specified role (+master+ or +slave+). In the example above, the cluster will choose a location based on where database is running as a +master+, and if there are multiple +master+ instances it will also factor in +myApp+'s own location preferences when deciding which location to choose. Colocation with regular clones and other promotable clone resources is also possible. In such cases, the set of allowed locations for the +rsc+ clone is (after role filtering) limited to nodes on which the +with-rsc+ promotable clone resource is (or will be) in the specified role. Placement is then performed as normal. ==== Using Promotable Clone Resources in Colocation Sets ==== .Additional colocation set options relevant to promotable clone resources [width="95%",cols="1m,1,<6",options="header",align="center"] |========================================================= |Field |Default |Description |role |Started |The role that 'all members' of the set must be in. Allowed values: +Started+, +Master+, +Slave+. indexterm:[role,Ordering Constraints] indexterm:[Constraints,Ordering,role] |========================================================= In the following example +B+'s master must be located on the same node as +A+'s master. Additionally resources +C+ and +D+ must be located on the same node as +A+'s and +B+'s masters. .Colocate C and D with A's and B's master instances ====== [source,XML] ------- ------- ====== ==== Using Promotable Clone Resources in Ordered Sets ==== .Additional ordered set options relevant to promotable clone resources [width="95%",cols="1m,1,<3",options="header",align="center"] |========================================================= |Field |Default |Description |action |value of +first-action+ |An additional attribute of ordering constraint sets that specifies the action that applies to 'all members' of the set. Allowed values: +start+, +stop+, +promote+, +demote+. indexterm:[action,Ordering Constraints] indexterm:[Constraints,Ordering,action] |========================================================= .Start C and D after first promoting A and B ====== [source,XML] ------- ------- ====== In the above example, +B+ cannot be promoted to a master role until +A+ has been promoted. Additionally, resources +C+ and +D+ must wait until +A+ and +B+ have been promoted before they can start. [[s-clone-stickiness]] === Clone Stickiness === indexterm:[resource-stickiness,Clones] To achieve a stable allocation pattern, clones are slightly sticky by default. If no value for +resource-stickiness+ is provided, the clone will use a value of 1. Being a small value, it causes minimal disturbance to the score calculations of other resources but is enough to prevent Pacemaker from needlessly moving copies around the cluster. [NOTE] ==== For globally unique clones, this may result in multiple instances of the clone staying on a single node, even after another eligible node becomes active (for example, after being put into standby mode then made active again). If you do not want this behavior, specify a +resource-stickiness+ of 0 for the clone temporarily and let the cluster adjust, then set it back to 1 if you want the default behavior to apply again. ==== +[IMPORTANT] +==== +If +resource-stickiness+ is set in the +rsc_defaults+ section, it will +apply to clone instances as well. This means an explicit +resource-stickiness+ +of 0 in +rsc_defaults+ works differently from the implicit default used when ++resource-stickiness+ is not specified. +==== + === Clone Resource Agent Requirements === Any resource can be used as an anonymous clone, as it requires no additional support from the resource agent. Whether it makes sense to do so depends on your resource and its resource agent. ==== Resource Agent Requirements for Globally Unique Clones ==== Globally unique clones require additional support in the resource agent. In particular, it must only respond with +$\{OCF_SUCCESS}+ if the node has that exact instance active. All other probes for instances of the clone should result in +$\{OCF_NOT_RUNNING}+ (or one of the other OCF error codes if they are failed). Individual instances of a clone are identified by appending a colon and a numerical offset, e.g. +apache:2+. Resource agents can find out how many copies there are by examining the +OCF_RESKEY_CRM_meta_clone_max+ environment variable and which instance it is by examining +OCF_RESKEY_CRM_meta_clone+. The resource agent must not make any assumptions (based on +OCF_RESKEY_CRM_meta_clone+) about which numerical instances are active. In particular, the list of active copies will not always be an unbroken sequence, nor always start at 0. ==== Resource Agent Requirements for Promotable Clones ==== Promotable clone resources require two extra actions, +demote+ and +promote+, which are responsible for changing the state of the resource. Like +start+ and +stop+, they should return +$\{OCF_SUCCESS}+ if they completed successfully or a relevant error code if they did not. The states can mean whatever you wish, but when the resource is started, it must come up in the mode called +slave+. From there the cluster will decide which instances to promote to +master+. In addition to the clone requirements for monitor actions, agents must also _accurately_ report which state they are in. The cluster relies on the agent to report its status (including role) accurately and does not indicate to the agent what role it currently believes it to be in. .Role implications of OCF return codes [width="95%",cols="1,<1",options="header",align="center"] |========================================================= |Monitor Return Code |Description |OCF_NOT_RUNNING |Stopped indexterm:[Return Code,OCF_NOT_RUNNING] |OCF_SUCCESS |Running (Slave) indexterm:[Return Code,OCF_SUCCESS] |OCF_RUNNING_MASTER |Running (Master) indexterm:[Return Code,OCF_RUNNING_MASTER] |OCF_FAILED_MASTER |Failed (Master) indexterm:[Return Code,OCF_FAILED_MASTER] |Other |Failed (Slave) |========================================================= ==== Clone Notifications ==== If the clone has the +notify+ meta-attribute set to +true+, and the resource agent supports the +notify+ action, Pacemaker will call the action when appropriate, passing a number of extra variables which, when combined with additional context, can be used to calculate the current state of the cluster and what is about to happen to it. .Environment variables supplied with Clone notify actions [width="95%",cols="5,<3",options="header",align="center"] |========================================================= |Variable |Description |OCF_RESKEY_CRM_meta_notify_type |Allowed values: +pre+, +post+ indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,type] indexterm:[type,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_operation |Allowed values: +start+, +stop+ indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,operation] indexterm:[operation,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_start_resource |Resources to be started indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,start_resource] indexterm:[start_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_stop_resource |Resources to be stopped indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,stop_resource] indexterm:[stop_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_active_resource |Resources that are running indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,active_resource] indexterm:[active_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_inactive_resource |Resources that are not running indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,inactive_resource] indexterm:[inactive_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_start_uname |Nodes on which resources will be started indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,start_uname] indexterm:[start_uname,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_stop_uname |Nodes on which resources will be stopped indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,stop_uname] indexterm:[stop_uname,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_active_uname |Nodes on which resources are running indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,active_uname] indexterm:[active_uname,Notification Environment Variable] |========================================================= The variables come in pairs, such as +OCF_RESKEY_CRM_meta_notify_start_resource+ and +OCF_RESKEY_CRM_meta_notify_start_uname+ and should be treated as an array of whitespace-separated elements. +OCF_RESKEY_CRM_meta_notify_inactive_resource+ is an exception as the matching +uname+ variable does not exist since inactive resources are not running on any node. Thus in order to indicate that +clone:0+ will be started on +sles-1+, +clone:2+ will be started on +sles-3+, and +clone:3+ will be started on +sles-2+, the cluster would set .Notification variables ====== [source,Bash] ------- OCF_RESKEY_CRM_meta_notify_start_resource="clone:0 clone:2 clone:3" OCF_RESKEY_CRM_meta_notify_start_uname="sles-1 sles-3 sles-2" ------- ====== +[NOTE] +==== +Pacemaker will log but otherwise ignore failures of notify actions. +==== + ==== Interpretation of Notification Variables ==== .Pre-notification (stop): * Active resources: +$OCF_RESKEY_CRM_meta_notify_active_resource+ * Inactive resources: +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ .Post-notification (stop) / Pre-notification (start): * Active resources ** +$OCF_RESKEY_CRM_meta_notify_active_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Inactive resources ** +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources that were started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources that were stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ .Post-notification (start): * Active resources: ** +$OCF_RESKEY_CRM_meta_notify_active_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Inactive resources: ** +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources that were started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources that were stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ==== Extra Notifications for Promotable Clones ==== .Extra environment variables supplied for promotable clones [width="95%",cols="5,<3",options="header",align="center"] |========================================================= |OCF_RESKEY_CRM_meta_notify_master_resource |Resources that are running in +Master+ mode indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,master_resource] indexterm:[master_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_slave_resource |Resources that are running in +Slave+ mode indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,slave_resource] indexterm:[slave_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_promote_resource |Resources to be promoted indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,promote_resource] indexterm:[promote_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_demote_resource |Resources to be demoted indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,demote_resource] indexterm:[demote_resource,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_promote_uname |Nodes on which resources will be promoted indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,promote_uname] indexterm:[promote_uname,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_demote_uname |Nodes on which resources will be demoted indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,demote_uname] indexterm:[demote_uname,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_master_uname |Nodes on which resources are running in +Master+ mode indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,master_uname] indexterm:[master_uname,Notification Environment Variable] |OCF_RESKEY_CRM_meta_notify_slave_uname |Nodes on which resources are running in +Slave+ mode indexterm:[Environment Variable,OCF_RESKEY_CRM_meta_notify_,slave_uname] indexterm:[slave_uname,Notification Environment Variable] |========================================================= ==== Interpretation of Promotable Notification Variables ==== .Pre-notification (demote): * +Active+ resources: +$OCF_RESKEY_CRM_meta_notify_active_resource+ * +Master+ resources: +$OCF_RESKEY_CRM_meta_notify_master_resource+ * +Slave+ resources: +$OCF_RESKEY_CRM_meta_notify_slave_resource+ * Inactive resources: +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources to be demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ .Post-notification (demote) / Pre-notification (stop): * +Active+ resources: +$OCF_RESKEY_CRM_meta_notify_active_resource+ * +Master+ resources: ** +$OCF_RESKEY_CRM_meta_notify_master_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * +Slave+ resources: +$OCF_RESKEY_CRM_meta_notify_slave_resource+ * Inactive resources: +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources to be demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources that were demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ .Post-notification (stop) / Pre-notification (start) * +Active+ resources: ** +$OCF_RESKEY_CRM_meta_notify_active_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * +Master+ resources: ** +$OCF_RESKEY_CRM_meta_notify_master_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * +Slave+ resources: ** +$OCF_RESKEY_CRM_meta_notify_slave_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Inactive resources: ** +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources to be demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources that were demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources that were stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ .Post-notification (start) / Pre-notification (promote) * +Active+ resources: ** +$OCF_RESKEY_CRM_meta_notify_active_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * +Master+ resources: ** +$OCF_RESKEY_CRM_meta_notify_master_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * +Slave+ resources: ** +$OCF_RESKEY_CRM_meta_notify_slave_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Inactive resources: ** +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources to be demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources that were started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources that were demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources that were stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ .Post-notification (promote) * +Active+ resources: ** +$OCF_RESKEY_CRM_meta_notify_active_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * +Master+ resources: ** +$OCF_RESKEY_CRM_meta_notify_master_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_demote_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * +Slave+ resources: ** +$OCF_RESKEY_CRM_meta_notify_slave_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_start_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Inactive resources: ** +$OCF_RESKEY_CRM_meta_notify_inactive_resource+ ** plus +$OCF_RESKEY_CRM_meta_notify_stop_resource+ ** minus +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources to be promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources to be demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources to be stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ * Resources that were started: +$OCF_RESKEY_CRM_meta_notify_start_resource+ * Resources that were promoted: +$OCF_RESKEY_CRM_meta_notify_promote_resource+ * Resources that were demoted: +$OCF_RESKEY_CRM_meta_notify_demote_resource+ * Resources that were stopped: +$OCF_RESKEY_CRM_meta_notify_stop_resource+ === Monitoring Promotable Clone Resources === The usual monitor actions are insufficient to monitor a promotable clone resource, because Pacemaker needs to verify not only that the resource is active, but also that its actual role matches its intended one. Define two monitoring actions: the usual one will cover the slave role, and an additional one with +role="master"+ will cover the master role. .Monitoring both states of a promotable clone resource ====== [source,XML] ------- ------- ====== [IMPORTANT] =========== It is crucial that _every_ monitor operation has a different interval! Pacemaker currently differentiates between operations only by resource and interval; so if (for example) a promotable clone resource had the same monitor interval for both roles, Pacemaker would ignore the role when checking the status -- which would cause unexpected return codes, and therefore unnecessary complications. =========== [[s-promotion-scores]] === Determining Which Instance is Promoted === Pacemaker can choose a promotable clone instance to be promoted in one of two ways: * Promotion scores: These are node attributes set via the `crm_master` utility, which generally would be called by the resource agent's start action if it supports promotable clones. This tool automatically detects both the resource and host, and should be used to set a preference for being promoted. Based on this, +promoted-max+, and +promoted-node-max+, the instance(s) with the highest preference will be promoted. * Constraints: Location constraints can indicate which nodes are most preferred as masters. .Explicitly preferring node1 to be promoted to master ====== [source,XML] ------- ------- ====== [[s-resource-bundle]] == Bundles - Isolated Environments == indexterm:[bundle] indexterm:[Resource,bundle] indexterm:[Docker,bundle] indexterm:[rkt,bundle] Pacemaker supports a special syntax for launching a https://en.wikipedia.org/wiki/Operating-system-level_virtualization[container] with any infrastructure it requires: the 'bundle'. Pacemaker bundles support https://www.docker.com/[Docker] and https://coreos.com/rkt/[rkt] container technologies. footnote:[Docker is a trademark of Docker, Inc. No endorsement by or association with Docker, Inc. is implied.] .A bundle for a containerized web server ==== [source,XML] ---- ---- ==== === Bundle Properties === .Properties of a Bundle [width="95%",cols="3m,<5",options="header",align="center"] |========================================================= |Field |Description |id |A unique name for the bundle (required) indexterm:[id,bundle] indexterm:[bundle,Property,id] |description |Arbitrary text (not used by Pacemaker) indexterm:[description,bundle] indexterm:[bundle,Property,description] |========================================================= A bundle must contain exactly one ++ or ++ element. === Docker Properties === Before configuring a Docker bundle in Pacemaker, the user must install Docker and supply a fully configured Docker image on every node allowed to run the bundle. Pacemaker will create an implicit +ocf:heartbeat:docker+ resource to manage a bundle's Docker container. The user must ensure that resource agent is installed on every node allowed to run the bundle. .Properties of a Bundle's Docker Element [width="95%",cols="3m,4,<5",options="header",align="center"] |========================================================= |Field |Default |Description |image | |Docker image tag (required) indexterm:[image,Docker] indexterm:[Docker,Property,image] |replicas |Value of +promoted-max+ if that is positive, else 1 |A positive integer specifying the number of container instances to launch indexterm:[replicas,Docker] indexterm:[Docker,Property,replicas] |replicas-per-host |1 |A positive integer specifying the number of container instances allowed to run on a single node indexterm:[replicas-per-host,Docker] indexterm:[Docker,Property,replicas-per-host] |promoted-max |0 |A non-negative integer that, if positive, indicates that the containerized service should be treated as a promotable service, with this many replicas allowed to run the service in the master role indexterm:[promoted-max,Docker] indexterm:[Docker,Property,promoted-max] |network | |If specified, this will be passed to +docker run+ as the https://docs.docker.com/engine/reference/run/#network-settings[network setting] for the Docker container. indexterm:[network,Docker] indexterm:[Docker,Property,network] |run-command |`/usr/sbin/pacemaker-remoted` if bundle contains a +primitive+, otherwise none |This command will be run inside the container when launching it ("PID 1"). If the bundle contains a +primitive+, this command 'must' start pacemaker-remoted (but could, for example, be a script that does other stuff, too). If the container image has a pre-2.0.0 version of Pacemaker, set this to +/usr/sbin/pacemaker_remoted+ (note the underbar instead of dash). indexterm:[run-command,Docker] indexterm:[Docker,Property,run-command] |options | |Extra command-line options to pass to `docker run` indexterm:[options,Docker] indexterm:[Docker,Property,options] |========================================================= For backward compatibility, +masters+ is accepted as an alias for +promoted-max+, but is deprecated since 2.0.0, and support for it will be removed in a future version. === rkt Properties === Before configuring a rkt bundle in Pacemaker, the user must install rkt and supply a fully configured container image on every node allowed to run the bundle. Pacemaker will create an implicit +ocf:heartbeat:rkt+ resource to manage a bundle's rkt container. The user must ensure that resource agent is installed on every node allowed to run the bundle. .Properties of a Bundle's rkt Element [width="95%",cols="3m,4,<5",options="header",align="center"] |========================================================= |Field |Default |Description |image | |Container image tag (required) indexterm:[image,rkt] indexterm:[rkt,Property,image] |replicas |Value of +promoted-max+ if that is positive, else 1 |A positive integer specifying the number of container instances to launch indexterm:[replicas,rkt] indexterm:[rkt,Property,replicas] |replicas-per-host |1 |A positive integer specifying the number of container instances allowed to run on a single node indexterm:[replicas-per-host,rkt] indexterm:[rkt,Property,replicas-per-host] |promoted-max |0 |A non-negative integer that, if positive, indicates that the containerized service should be treated as a promotable service, with this many replicas allowed to run the service in the master role indexterm:[promoted-max,rkt] indexterm:[rkt,Property,promoted-max] |network | |If specified, this will be passed to +rkt run+ as the network setting for the rkt container. indexterm:[network,rkt] indexterm:[rkt,Property,network] |run-command |`/usr/sbin/pacemaker-remoted` if bundle contains a +primitive+, otherwise none |This command will be run inside the container when launching it ("PID 1"). If the bundle contains a +primitive+, this command 'must' start pacemaker-remoted (but could, for example, be a script that does other stuff, too). If the container image has a pre-2.0.0 version of Pacemaker, set this to +/usr/sbin/pacemaker_remoted+ (note the underbar instead of dash). indexterm:[run-command,rkt] indexterm:[rkt,Property,run-command] |options | |Extra command-line options to pass to `rkt run` indexterm:[options,rkt] indexterm:[rkt,Property,options] |========================================================= For backward compatibility, +masters+ is accepted as an alias for +promoted-max+, but is deprecated since 2.0.0, and support for it will be removed in a future version. === Bundle Network Properties === A bundle may optionally contain one ++ element. indexterm:[bundle,network] .Properties of a Bundle's Network Element [width="95%",cols="2m,1,<4",options="header",align="center"] |========================================================= |Field |Default |Description |add-host |TRUE |If TRUE, and +ip-range-start+ is used, Pacemaker will automatically ensure that +/etc/hosts+ inside the containers has entries for each <> and its assigned IP. indexterm:[add-host,network] indexterm:[network,Property,add-host] |ip-range-start | |If specified, Pacemaker will create an implicit +ocf:heartbeat:IPaddr2+ resource for each container instance, starting with this IP address, using up to +replicas+ sequential addresses. These addresses can be used from the host's network to reach the service inside the container, though it is not visible within the container itself. Only IPv4 addresses are currently supported. indexterm:[ip-range-start,network] indexterm:[network,Property,ip-range-start] |host-netmask |32 |If +ip-range-start+ is specified, the IP addresses are created with this CIDR netmask (as a number of bits). indexterm:[host-netmask,network] indexterm:[network,Property,host-netmask] |host-interface | |If +ip-range-start+ is specified, the IP addresses are created on this host interface (by default, it will be determined from the IP address). indexterm:[host-interface,network] indexterm:[network,Property,host-interface] |control-port |3121 |If the bundle contains a +primitive+, the cluster will use this integer TCP port for communication with Pacemaker Remote inside the container. Changing this is useful when the container is unable to listen on the default port, for example, when the container uses the host's network rather than +ip-range-start+ (in which case +replicas-per-host+ must be 1), or when the bundle may run on a Pacemaker Remote node that is already listening on the default port. Any PCMK_remote_port environment variable set on the host or in the container is ignored for bundle connections. indexterm:[control-port,network] indexterm:[network,Property,control-port] |========================================================= [[s-resource-bundle-note-replica-names]] [NOTE] ==== Replicas are named by the bundle id plus a dash and an integer counter starting with zero. For example, if a bundle named +httpd-bundle+ has +replicas=2+, its containers will be named +httpd-bundle-0+ and +httpd-bundle-1+. ==== Additionally, a ++ element may optionally contain one or more ++ elements. indexterm:[bundle,network,port-mapping] .Properties of a Bundle's Port-Mapping Element [width="95%",cols="2m,1,<4",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the port mapping (required) indexterm:[id,port-mapping] indexterm:[port-mapping,Property,id] |port | |If this is specified, connections to this TCP port number on the host network (on the container's assigned IP address, if +ip-range-start+ is specified) will be forwarded to the container network. Exactly one of +port+ or +range+ must be specified in a +port-mapping+. indexterm:[port,port-mapping] indexterm:[port-mapping,Property,port] |internal-port |value of +port+ |If +port+ and this are specified, connections to +port+ on the host's network will be forwarded to this port on the container network. indexterm:[internal-port,port-mapping] indexterm:[port-mapping,Property,internal-port] |range | |If this is specified, connections to these TCP port numbers (expressed as 'first_port'-'last_port') on the host network (on the container's assigned IP address, if +ip-range-start+ is specified) will be forwarded to the same ports in the container network. Exactly one of +port+ or +range+ must be specified in a +port-mapping+. indexterm:[range,port-mapping] indexterm:[port-mapping,Property,range] |========================================================= [NOTE] ==== If the bundle contains a +primitive+, Pacemaker will automatically map the +control-port+, so it is not necessary to specify that port in a +port-mapping+. ==== === Bundle Storage Properties === A bundle may optionally contain one ++ element. A ++ element has no properties of its own, but may contain one or more ++ elements. indexterm:[bundle,storage,storage-mapping] .Properties of a Bundle's Storage-Mapping Element [width="95%",cols="2m,1,<4",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the storage mapping (required) indexterm:[id,storage-mapping] indexterm:[storage-mapping,Property,id] |source-dir | |The absolute path on the host's filesystem that will be mapped into the container. Exactly one of +source-dir+ and +source-dir-root+ must be specified in a +storage-mapping+. indexterm:[source-dir,storage-mapping] indexterm:[storage-mapping,Property,source-dir] |source-dir-root | |The start of a path on the host's filesystem that will be mapped into the container, using a different subdirectory on the host for each container instance. The subdirectory will be named the same as the <>. Exactly one of +source-dir+ and +source-dir-root+ must be specified in a +storage-mapping+. indexterm:[source-dir-root,storage-mapping] indexterm:[storage-mapping,Property,source-dir-root] |target-dir | |The path name within the container where the host storage will be mapped (required) indexterm:[target-dir,storage-mapping] indexterm:[storage-mapping,Property,target-dir] |options | |File system mount options to use when mapping the storage indexterm:[options,storage-mapping] indexterm:[storage-mapping,Property,options] |========================================================= [NOTE] ==== Pacemaker does not define the behavior if the source directory does not already exist on the host. However, it is expected that the container technology and/or its resource agent will create the source directory in that case. ==== [NOTE] ==== If the bundle contains a +primitive+, Pacemaker will automatically map the equivalent of +source-dir=/etc/pacemaker/authkey target-dir=/etc/pacemaker/authkey+ and +source-dir-root=/var/log/pacemaker/bundles target-dir=/var/log+ into the container, so it is not necessary to specify those paths in a +storage-mapping+. ==== [IMPORTANT] ==== The +PCMK_authkey_location+ environment variable must not be set to anything other than the default of `/etc/pacemaker/authkey` on any node in the cluster. ==== === Bundle Primitive === A bundle may optionally contain one ++ resource (see <>). The primitive may have operations, instance attributes and meta-attributes defined, as usual. If a bundle contains a primitive resource, the container image must include the Pacemaker Remote daemon, and at least one of +ip-range-start+ or +control-port+ must be configured in the bundle. Pacemaker will create an implicit +ocf:pacemaker:remote+ resource for the connection, launch Pacemaker Remote within the container, and monitor and manage the primitive resource via Pacemaker Remote. If the bundle has more than one container instance (replica), the primitive resource will function as an implicit clone (see <>) -- a promotable clone if the bundle has +masters+ greater than zero (see <>). [IMPORTANT] ==== Containers in bundles with a +primitive+ must have an accessible networking environment, so that Pacemaker on the cluster nodes can contact Pacemaker Remote inside the container. For example, the Docker option `--net=none` should not be used with a +primitive+. The default (using a distinct network space inside the container) works in combination with +ip-range-start+. If the Docker option `--net=host` is used (making the container share the host's network space), a unique +control-port+ should be specified for each bundle. Any firewall must allow access to the +control-port+. ==== [[s-bundle-attributes]] === Bundle Node Attributes === If the bundle has a +primitive+, the primitive's resource agent may want to set node attributes such as <>. However, with containers, it is not apparent which node should get the attribute. If the container uses shared storage that is the same no matter which node the container is hosted on, then it is appropriate to use the promotion score on the bundle node itself. On the other hand, if the container uses storage exported from the underlying host, then it may be more appropriate to use the promotion score on the underlying host. Since this depends on the particular situation, the +container-attribute-target+ resource meta-attribute allows the user to specify which approach to use. If it is set to +host+, then user-defined node attributes will be checked on the underlying host. If it is anything else, the local node (in this case the bundle node) is used as usual. This only applies to user-defined attributes; the cluster will always check the local node for cluster-defined attributes such as +#uname+. If +container-attribute-target+ is +host+, the cluster will pass additional environment variables to the primitive's resource agent that allow it to set node attributes appropriately: +CRM_meta_container_attribute_target+ (identical to the meta-attribute value) and +CRM_meta_physical_host+ (the name of the underlying host). [NOTE] ==== When called by a resource agent, the attrd_updater and crm_attribute commands will automatically check those environment variables and set attributes appropriately. ==== === Bundle Meta-Attributes === Any meta-attribute set on a bundle will be inherited by the bundle's primitive and any resources implicitly created by Pacemaker for the bundle. This includes options such as +priority+, +target-role+, and +is-managed+. See <> for more information. === Limitations of Bundles === Restarting pacemaker while a bundle is unmanaged or the cluster is in maintenance mode may cause the bundle to fail. Bundles may not be explicitly cloned or included in groups. This includes the bundle's primitive and any resources implicitly created by Pacemaker for the bundle. (If +replicas+ is greater than 1, the bundle will behave like a clone implicitly.) Bundles do not have instance attributes, utilization attributes, or operations, though a bundle's primitive may have them. A bundle with a primitive can run on a Pacemaker Remote node only if the bundle uses a distinct +control-port+. diff --git a/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt b/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt index 32b959e03f..3f76d8a475 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Constraints.txt @@ -1,882 +1,887 @@ :compat-mode: legacy = Resource Constraints = +//// +We prefer [[ch-constraints]], but older versions of asciidoc don't deal well +with that construct for chapter headings +//// +anchor:ch-constraints[Chapter 7, Alerts] 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 per resource and node. Any node with a negative score for a resource can't run that resource. The cluster places a resource on the node with the highest score for it. === Infinity Math === Pacemaker implements +INFINITY+ (or equivalently, ++INFINITY+) internally as a score of 1,000,000. Addition and subtraction with it follow these three basic rules: * Any value + +INFINITY+ = +INFINITY+ * Any value - +INFINITY+ = +-INFINITY+ * +INFINITY+ - +INFINITY+ = +-INFINITY+ [NOTE] ====== What if you want to use a score higher than 1,000,000? Typically this possibility arises when someone wants to base the score on some external metric that might go above 1,000,000. The short answer is you can't. The long answer is it is sometimes possible work around this limitation creatively. You may be able to set the score to some computed value based on the external metric rather than use the metric directly. For nodes, you can store the metric as a node attribute, and query the attribute when computing the score (possibly as part of a custom resource agent). ====== == Deciding Which Nodes a Resource Can Run On == indexterm:[Location Constraints] indexterm:[Resource,Constraints,Location] 'Location constraints' tell the cluster which nodes a resource can run on. There are two alternative strategies. One way is to say that, by default, resources can run anywhere, and then the location constraints specify nodes that are not allowed (an 'opt-out' cluster). The other way is to start with nothing able to run anywhere, and use location constraints to selectively enable allowed nodes (an 'opt-in' cluster). Whether you should choose opt-in or opt-out depends 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. === Location Properties === .Properties of a rsc_location Constraint [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 | |The name of the resource to which this constraint applies indexterm:[rsc,Location Constraints] indexterm:[Constraints,Location,rsc] |rsc-pattern | |An extended regular expression (as defined in http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04[POSIX]) matching the names of resources to which this constraint applies, if +rsc+ is not specified; if the regular expression contains submatches and the constraint is governed by a rule (see <>), the submatches can be referenced as +%0+ through +%9+ in the rule's +score-attribute+ or a rule expression's +attribute+ indexterm:[rsc-pattern,Location Constraints] indexterm:[Constraints,Location,rsc-pattern] |node | |A node's name indexterm:[node,Location Constraints] indexterm:[Constraints,Location,node] |score | |Positive values indicate a preference for running the affected resource(s) on this node -- the higher the value, the stronger the preference. Negative values indicate the resource(s) should avoid this node (a value of +-INFINITY+ changes "should" to "must"). indexterm:[score,Location Constraints] indexterm:[Constraints,Location,score] |resource-discovery |always a|Whether Pacemaker should perform resource discovery (that is, check whether the resource is already running) for this resource on this node. This should normally be left as the default, so that rogue instances of a service can be stopped when they are running where they are not supposed to be. However, there are two situations where disabling resource discovery is a good idea: when a service is not installed on a node, discovery might return an error (properly written OCF agents will not, so this is usually only seen with other agent types); and when Pacemaker Remote is used to scale a cluster to hundreds of nodes, limiting resource discovery to allowed nodes can significantly boost performance. * +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:+ Perform resource discovery for the specified resource only on this node (and other nodes similarly marked as +exclusive+). 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] |========================================================= [WARNING] ========= Setting resource-discovery to +never+ or +exclusive+ removes Pacemaker's ability to detect and stop unwanted instances of a service running where it's not supposed to be. It is up to the system administrator (you!) to make sure that the service can 'never' be active on nodes without resource-discovery (such as by leaving the relevant software uninstalled). ========= === 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: ---- # crm_attribute --name symmetric-cluster --update 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. .Opt-in location constraints for two resources ====== [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: ---- # crm_attribute --name symmetric-cluster --update true ---- Then start disabling nodes. The following fragment is the equivalent of the above opt-in configuration. .Opt-out location constraints for two resources ====== [source,XML] ------- ------- ====== [[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. .Constraints where a resource prefers 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 the Order in which Resources Should Start/Stop == indexterm:[Resource,Constraints,Ordering] indexterm:[Resource,Start Order] indexterm:[Ordering Constraints] 'Ordering constraints' tell the cluster the order in which resources should start. [IMPORTANT] ==== Ordering constraints affect 'only' the ordering of resources; they do 'not' require that the resources be placed on the same node. If you want resources to be started on the same node 'and' in a specific order, you need both an ordering constraint 'and' a colocation constraint (see <>), or alternatively, a group (see <>). ==== === Ordering Properties === .Properties of a rsc_order Constraint [width="95%",cols="1m,1,<4",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the constraint indexterm:[id,Ordering Constraints] indexterm:[Constraints,Ordering,id] |first | |Name of the resource that the +then+ resource depends on indexterm:[first,Ordering Constraints] indexterm:[Constraints,Ordering,first] |then | |Name of the dependent resource indexterm:[then,Ordering Constraints] indexterm:[Constraints,Ordering,then] |first-action |start |The action that the +first+ resource must complete before +then-action+ can be initiated for the +then+ resource. Allowed values: +start+, +stop+, +promote+, +demote+. indexterm:[first-action,Ordering Constraints] indexterm:[Constraints,Ordering,first-action] |then-action |value of +first-action+ |The action that the +then+ resource can execute only after the +first-action+ on the +first+ resource has completed. Allowed values: +start+, +stop+, +promote+, +demote+. indexterm:[then-action,Ordering Constraints] indexterm:[Constraints,Ordering,then-action] |kind |Mandatory a|How to enforce the constraint. Allowed values: * +Optional:+ Just a suggestion. Only applies if both resources are executing the specified actions. Any change in state by the +first+ resource will have no effect on the +then+ resource. * +Mandatory:+ Always. If +first+ does not perform +first-action+, +then+ will not be allowed to performed +then-action+. If +first+ is restarted, +then+ (if running) will be stopped beforehand and started afterward. * +Serialize:+ Ensure that no two stop/start actions occur concurrently for the resources. +First+ and +then+ can start in either order, but one must complete starting before the other can be started. A typical use case is when resource start-up puts a high load on the host. indexterm:[kind,Ordering Constraints] indexterm:[Constraints,Ordering,kind] |symmetrical |TRUE for +Mandatory+ and +Optional+ kinds. FALSE for +Serialize+ kind. |If true, the reverse of the constraint applies for the opposite action (for example, if B starts after A starts, then B stops before A stops). +Serialize+ orders cannot be symmetrical. indexterm:[symmetrical,Ordering Constraints] indexterm:[Ordering Constraints,symmetrical] |========================================================= +Promote+ and +demote+ apply to the master role of <> resources. === Optional and mandatory ordering === Here is an example of ordering constraints where +Database+ 'must' start before +Webserver+, and +IP+ 'should' start before +Webserver+ if they both need to be started: .Optional and mandatory ordering constraints ====== [source,XML] ------- ------- ====== Because the above example lets +symmetrical+ default to TRUE, +Webserver+ must be stopped before +Database+ can be stopped, and +Webserver+ should be stopped before +IP+ if they both need to be stopped. [[s-resource-colocation]] == Placing Resources Relative to other Resources == indexterm:[Resource,Constraints,Colocation] indexterm:[Resource,Location Relative to other Resources] 'Colocation constraints' tell the cluster that the location of one resource depends on the location of another one. Colocation has an important side-effect: it affects the order in which resources are assigned to a node. Think about it: 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 colocated with B, the cluster will take into account A's preferences when deciding which node to choose for B. For a detailed look at exactly how this occurs, see http://clusterlabs.org/doc/Colocation_Explained.pdf[Colocation Explained]. [IMPORTANT] ==== Colocation constraints affect 'only' the placement of resources; they do 'not' require that the resources be started in a particular order. If you want resources to be started on the same node 'and' in a specific order, you need both an ordering constraint (see <>) 'and' a colocation constraint, or alternatively, a group (see <>). ==== === Colocation Properties === .Properties of a rsc_colocation Constraint [width="95%",cols="1m,1,<4",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the constraint (required). indexterm:[id,Colocation Constraints] indexterm:[Constraints,Colocation,id] |rsc | |The name of a resource that should be located relative to +with-rsc+ (required). indexterm:[rsc,Colocation Constraints] indexterm:[Constraints,Colocation,rsc] |with-rsc | |The name of the resource used as the colocation target. The cluster will decide where to put this resource first and then decide where to put +rsc+ (required). indexterm:[with-rsc,Colocation Constraints] indexterm:[Constraints,Colocation,with-rsc] |node-attribute |#uname |The node attribute that must be the same on the node running +rsc+ and the node running +with-rsc+ for the constraint to be satisfied. (For details, see <>.) indexterm:[node-attribute,Colocation Constraints] indexterm:[Constraints,Colocation,node-attribute] |score | |Positive values indicate the resources should run on the same node. Negative values indicate the resources should run on different nodes. Values of \+/- +INFINITY+ change "should" to "must". indexterm:[score,Colocation Constraints] indexterm:[Constraints,Colocation,score] |========================================================= === Mandatory Placement === Mandatory placement occurs when 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 resource +A+ to always run on the same machine as resource +B+, you would add the following constraint: .Mandatory colocation constraint for two resources ==== [source,XML] ==== Remember, because +INFINITY+ was used, if +B+ can't run on any of the cluster nodes (for whatever reason) then +A+ will not be allowed to run. Whether +A+ is running or not has no effect on +B+. Alternatively, you may want the opposite -- that +A+ 'cannot' run on the same machine as +B+. In this case, use +score="-INFINITY"+. .Mandatory anti-colocation constraint for two resources ==== [source,XML] ==== Again, by specifying +-INFINITY+, the constraint is binding. So if the only place left to run is where +B+ already is, then +A+ may not run anywhere. As with +INFINITY+, +B+ can run even if +A+ is stopped. However, in this case +A+ also can run if +B+ is stopped, because it still meets the constraint of +A+ and +B+ not running on the same node. === 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 to accommodate your wishes but may ignore them if the alternative is to stop some of the cluster resources. As 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. .Advisory colocation constraint for two resources ==== [source,XML] ==== [[s-coloc-attribute]] === Colocation by Node Attribute === The +node-attribute+ property of a colocation constraints allows you to express the requirement, "these resources must be on similar nodes". As an example, imagine that you have two Storage Area Networks (SANs) that are not controlled by the cluster, and each node is connected to one or the other. You may have two resources +r1+ and +r2+ such that +r2+ needs to use the same SAN as +r1+, but doesn't necessarily have to be on the same exact node. In such a case, you could define a <> named +san+, with the value +san1+ or +san2+ on each node as appropriate. Then, you could colocate +r2+ with +r1+ using +node-attribute+ set to +san+. [[s-resource-sets]] == Resource Sets == 'Resource sets' allow multiple resources to be affected by a single constraint. .A set of 3 resources ==== [source,XML] ---- ---- ==== Resource sets are valid inside +rsc_location+, +rsc_order+ (see <>), +rsc_colocation+ (see <>), and +rsc_ticket+ (see <>) constraints. A resource set has a number of properties that can be set, though not all have an effect in all contexts. .Properties of a resource_set [width="95%",cols="2m,1,<5",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the set indexterm:[id,Resource Sets] indexterm:[Constraints,Resource Sets,id] |sequential |true |Whether the members of the set must be acted on in order. Meaningful within +rsc_order+ and +rsc_colocation+. indexterm:[sequential,Resource Sets] indexterm:[Constraints,Resource Sets,sequential] |require-all |true |Whether all members of the set must be active before continuing. With the current implementation, the cluster may continue even if only one member of the set is started, but if more than one member of the set is starting at the same time, the cluster will still wait until all of those have started before continuing (this may change in future versions). Meaningful within +rsc_order+. indexterm:[require-all,Resource Sets] indexterm:[Constraints,Resource Sets,require-all] |role | |Limit the effect of the constraint to the specified role. Meaningful within +rsc_location+, +rsc_colocation+ and +rsc_ticket+. indexterm:[role,Resource Sets] indexterm:[Constraints,Resource Sets,role] |action | |Limit the effect of the constraint to the specified action. Meaningful within +rsc_order+. indexterm:[action,Resource Sets] indexterm:[Constraints,Resource Sets,action] |score | |'Advanced use only.' Use a specific score for this set within the constraint. indexterm:[score,Resource Sets] indexterm:[Constraints,Resource Sets,score] |========================================================= [[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, resource sets (see <>) can be used within ordering constraints: .A chain of ordered resources expressed as a set ====== [source,XML] ------- ------- ====== While the set-based format is not less verbose, it is significantly easier to get right and maintain. [IMPORTANT] ========= If you use a higher-level tool, pay attention to how it exposes this functionality. Depending on the tool, creating a set +A B+ may be equivalent to +A then B+, or +B then A+. ========= === Ordering Multiple Sets === The syntax can be expanded to allow sets of resources to be ordered relative to each other, where the members of each individual set may be ordered or unordered (controlled by the +sequential+ property). In the example below, +A+ and +B+ can both start in parallel, as can +C+ and +D+, however +C+ and +D+ can only start once _both_ +A+ _and_ +B+ 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"] [IMPORTANT] ==== An ordered set with +sequential=false+ makes sense only if there is another set in the constraint. Otherwise, the constraint has no effect. ==== === 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 to 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. This option defaults to TRUE which is why the "AND" logic is used by default. Setting +require-all=false+ means only one resource in the set needs to be started before continuing on to the next set. .Resource Set "OR" logic: Three ordered sets, where the first set is internally unordered with "OR" logic ====== [source,XML] ------- ------- ====== [IMPORTANT] ==== An ordered set with +require-all=false+ makes sense only in conjunction with +sequential=false+. Think of it like this: +sequential=false+ modifies the set to be an unordered set using "AND" logic by default, and adding +require-all=false+ flips the unordered set's "AND" logic to "OR" logic. ==== [[s-resource-sets-colocation]] == Colocating Sets of Resources == Another common situation is for an administrator to create a set of colocated resources. One way to do this would be to define a resource group (see <>), but that cannot always accurately express the desired state. Another way would be to define each relationship as an individual constraint, but that causes a constraint explosion as the number of resources and combinations grow. An example of this approach: .Chain of colocated resources ====== [source,XML] ------- ------- ====== To make things easier, resource sets (see <>) can be used within colocation constraints. As with the chained version, a resource that can't be active prevents any resource that must be colocated with it from being active. For example, if +B+ is not able to run, then both +C+ and by inference +D+ must also remain stopped. Here is an example +resource_set+: .Equivalent colocation chain expressed using +resource_set+ ====== [source,XML] ------- ------- ====== [IMPORTANT] ========= If you use a higher-level tool, pay attention to how it exposes this functionality. Depending on the tool, creating a set +A B+ may be equivalent to +A with B+, or +B with A+. ========= This notation can also be used to tell the cluster that sets of resources must be colocated relative to each other, where the individual members of each set may or may not depend on each other being active (controlled by the +sequential+ property). In this example, +A+, +B+, and +C+ will each be colocated with +D+. +D+ must be active, but any of +A+, +B+, or +C+ may be inactive without affecting any other resources. .Using colocated sets to specify a common peer ====== [source,XML] ------- ------- ====== [IMPORTANT] ==== A colocated set with +sequential=false+ makes sense only if there is another set in the constraint. Otherwise, the constraint has no effect. ==== There is no inherent limit to the number and size of the sets used. The only thing that matters is that in order for any member of one set in the constraint to be active, all members of sets listed after it must also be active (and naturally on the same node); and if a set has +sequential="true"+, then in order for one member of that set to be active, all members listed before it must also be active. If desired, you can restrict the dependency to instances of promotable clone resources that are in a specific role, using the set's +role+ property. .Colocation chain in which the members of the middle set have no interdependencies, and the last listed set (which the cluster places first) is restricted to instances in master status. ====== [source,XML] ------- ------- ====== .Visual representation the above example (resources to the left are placed first) image::images/three-sets-complex.png["Colocation chain",width="16cm",height="9cm",align="center"] [NOTE] ==== Pay close attention to the order in which resources and sets are listed. While the colocation dependency for members of any one set is last-to-first, the colocation dependency for multiple sets is first-to-last. In the above example, +B+ is colocated with +A+, but +colocated-set-1+ is colocated with +colocated-set-2+. Unlike ordered sets, colocated sets do not use the +require-all+ option. ==== 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 1ae131fbf2..0d8f289281 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Multi-site-Clusters.txt @@ -1,334 +1,340 @@ :compat-mode: legacy = Multi-Site Clusters and Tickets = Apart from local clusters, Pacemaker also supports multi-site clusters. That means you can have multiple, geographically dispersed sites, each with a local cluster. Failover between these clusters can be coordinated manually by the administrator, or automatically by a higher-level entity called a 'Cluster Ticket Registry (CTR)'. == Challenges for Multi-Site Clusters == Typically, multi-site environments are too far apart to support synchronous communication and data replication between the sites. That leads to significant challenges: - How do we make sure that a cluster site is up and running? - How do we make sure that resources are only started once? - How do we make sure that quorum can be reached between the different sites and a split-brain scenario avoided? - How do we manage failover between sites? - How do we 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 in order to guarantee that any cluster resource will be active on no more than one cluster site. This is achieved by using 'tickets' that are treated as failover domain between cluster sites, in case a site should be down. The following sections explain the individual components and mechanisms that were introduced for multi-site clusters in more detail. === 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+ constraints. Only if the ticket is available at a site can the respective resources be started there. Vice versa, if the ticket is revoked, the resources depending on that ticket must 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.) Tickets can be granted and revoked either manually by administrators (which could be the default for classic enterprise clusters), or via the automated CTR mechanism described 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 the same as the value +false+. === Dead Man Dependency === A site can only activate 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 a dead man dependency is in force, if a 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. === Cluster Ticket Registry === A CTR is a coordinated group of network daemons that automatically handles granting, revoking, and timing out tickets (instead of the administrator revoking the ticket somewhere, waiting for everything to stop, and then granting it on the desired site). Pacemaker does not implement its own CTR, but interoperates with external software designed for that purpose (similar to how resource and fencing agents are not directly part of pacemaker). Participating clusters run the CTR daemons, which connect to each other, exchange information about their connectivity, and vote on which sites gets which tickets. A ticket is granted to a site only once the CTR is sure that the ticket has been relinquished by the previous owner, 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. [[s-ticket-constraints]] == 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. .Constraint that fences node if +ticketA+ is revoked ==== [source,XML] ------- ------- ==== The example above 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 if +ticketA+ is revoked. If resource +rsc1+ were a promotable resource (i.e. it could run in master or slave mode), you might want to configure that only master mode depends on +ticketA+. With the following configuration, +rsc1+ will be demoted to slave mode if +ticketA+ is revoked: .Constraint that demotes +rsc1+ if +ticketA+ is revoked ==== [source,XML] ------- ------- ==== You can create multiple `rsc_ticket` constraints to let multiple resources depend on the same ticket. However, `rsc_ticket` also supports resource sets (see <>), so one can easily list all the resources in one `rsc_ticket` constraint instead. .Ticket constraint for multiple resources ==== [source,XML] ------- ------- ==== In the example above, there are two resource sets, so we can list resources with different roles in a single +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. If you want to re-distribute a ticket, you should wait for the dependent resources to stop cleanly at the previous site before you grant the ticket to the new site. Use the `crm_ticket` command line tool to grant and revoke tickets. +//// +These commands will actually just print a message telling the user that they +requre '--force'. That is probably a good exercise rather than letting novice +users cut and paste '--force' here. +//// + To grant a ticket to this site: ------- # crm_ticket --ticket ticketA --grant ------- To revoke a ticket from this site: ------- # crm_ticket --ticket ticketA --revoke ------- [IMPORTANT] ==== If you are managing tickets manually, use the `crm_ticket` command with great care, because it cannot check whether the same ticket is already granted elsewhere. ==== === Granting and Revoking Tickets via a Cluster Ticket Registry === We will use https://github.com/ClusterLabs/booth[Booth] here as an example of software that can be used with pacemaker as a Cluster Ticket Registry. Booth implements the http://en.wikipedia.org/wiki/Raft_%28computer_science%29[Raft] algorithm to guarantee the distributed consensus among different cluster sites, and manages the ticket distribution (and thus the failover process between sites). Each of the participating clusters and 'arbitrators' runs the Booth daemon `boothd`. An 'arbitrator' is the multi-site equivalent of a quorum-only node in a local cluster. 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. An arbitrator is especially important for a two-site scenario, otherwise there is no way for one site to distinguish between a network failure between it and the other site, and a failure of the other site. The most common multi-site 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. `Boothd` at each site connects to its peers 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 the `booth` command-line tool. After you have initially granted a ticket to a site, `boothd` will take over and manage the ticket automatically. [IMPORTANT] ==== The `booth` command-line tool can be used to grant, list, or revoke tickets and can be run on any machine where `boothd` is running. If you are managing tickets via Booth, use only `booth` for manual intervention, not `crm_ticket`. That ensures the same ticket will only be owned by one cluster site at a time. ==== ==== Booth 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. * 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: ------- # crm_ticket --info ------- Or you can monitor them with: ------- # crm_mon --tickets ------- Display the +rsc_ticket+ constraints that apply to a ticket: ------- # crm_ticket --ticket ticketA --constraints ------- When you want to do maintenance or manual switch-over of a ticket, revoking the ticket would trigger the loss policies. If +loss-policy="fence"+, the dependent resources could not be gracefully stopped/demoted, and other unrelated resources could even be affected. The proper way is making the ticket 'standby' first with: ------- # 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: ------- # crm_ticket --ticket ticketA --activate ------- == For more information == * https://www.suse.com/documentation/sle-ha-geo-12/art_ha_geo_quick/data/art_ha_geo_quick.html[SUSE's Geo Clustering quick start] * https://github.com/ClusterLabs/booth[Booth] diff --git a/doc/Pacemaker_Explained/en-US/Ch-Resources.txt b/doc/Pacemaker_Explained/en-US/Ch-Resources.txt index 61710b64b9..4fa69cd5b1 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Resources.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Resources.txt @@ -1,887 +1,897 @@ :compat-mode: legacy = Cluster Resources = [[s-resource-primitive]] == What is a Cluster Resource? == indexterm:[Resource] A resource is a service made highly available by a cluster. The simplest type of resource, a 'primitive' resource, is described in this chapter. More complex forms, such as groups and clones, are described in later chapters. Every primitive resource has a 'resource agent'. A resource agent is an external program that abstracts the service it provides and present a consistent view to the cluster. This 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]] == Resource Classes == indexterm:[Resource,class] Pacemaker supports several classes of agents: * OCF * LSB * Upstart * Systemd * Service * Fencing * Nagios Plugins === Open Cluster Framework === indexterm:[Resource,OCF] indexterm:[OCF,Resources] indexterm:[Open Cluster Framework,Resources] The OCF standard footnote:[See http://www.opencf.org/cgi-bin/viewcvs.cgi/specs/ra/resource-agent-api.txt?rev=HEAD -- at least as it relates to resource agents. 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 * make them extensible OCF specs have strict definitions of the exit codes that actions must return. footnote:[ The resource-agents source code includes 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 resource agent as environment variables, with the special prefix +OCF_RESKEY_+. So, a parameter which the user thinks of as +ip+ will be passed to the resource agent as +OCF_RESKEY_ip+. The number and purpose of the parameters is left to the resource agent; however, the resource agent should use the `meta-data` command to advertise any that it supports. The OCF class is the most preferred 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 the 'Resource Agents' chapter of 'Pacemaker Administration'. === Linux Standard Base === indexterm:[Resource,LSB] indexterm:[LSB,Resources] indexterm:[Linux Standard Base,Resources] -'LSB' resource agents are rather known as 'init scripts' (service startup -scripts), located in +/etc/init.d+. +'LSB' resource agents are more commonly known as 'init scripts'. If a full path +is not given, they are assumed to be located in +/etc/init.d+. -Commonly, they are provided by the OS distribution and, in order to be used -with the cluster, they must conform to the LSB Spec. +Commonly, they are provided by the OS distribution. In order to be used +with a Pacemaker cluster, they must conform to the LSB specification. 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. ] [WARNING] ==== Many distributions or particular software packages claim LSB compliance but ship with broken init scripts. For details on how to check whether your init script is LSB-compatible, see the 'Resource Agents' chapter of 'Pacemaker Administration'. Common problematic violations of the LSB standard include: * 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 * Stopping a stopped resource returns an error - -Since the LSB standard is pragmatic enough so as _not_ to elaborate -on clean and reliable (busy-waiting-free) service dependency chains beyond -symbolic system facilities names to order against (one of the strongest -guarantees set forth is with _syslog_ in particular, denoting that, -when satisfied, it's actually _operational_ -- something not demanded -universally with the standard) and because explicit dependency-based -ordering is crucial for stacked HA applications, additionally this -imminent setback, possibly rooted deeper in the lack of synchronization -after initial forking in daemons themselves (something that currently -spoils also Pacemaker's own user-facing ones) and hence nothing init -scripts alone could be blamed for, stands out: - -* Insufficient causality discreetness on either service start-up (for - the dependency chains, it's rather essential the service is also - _operational_, with the minimal viable interpretation being that - subsequent +status+ returns success but preferably in the strict - sense, once the respective init script invocation finishes with - success) or shutdown (ditto with no child processes left behind) -footnote:[ -There's an inherent difference between _started_ and _ready_ state -of the service at hand, see discussion at -https://jdebp.eu/FGA/unix-daemon-readiness-protocol-problems.html -also showing how suitably prepared <> may possibly improve on this through a native arrangement scheme. -] ==== [IMPORTANT] ==== Remember to make sure the computer is _not_ configured to start any services at boot time -- that should be controlled by the cluster. ==== [[s-resource-supported-systemd]] === Systemd === indexterm:[Resource,Systemd] indexterm:[Systemd,Resources] Some newer distributions have replaced the old http://en.wikipedia.org/wiki/Init#SysV-style["SysV"] 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 (unit files) are provided by the OS distribution, but there are online guides for converting from init scripts. footnote:[For example, http://0pointer.de/blog/projects/systemd-for-admins-3.html] [IMPORTANT] ==== 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["SysV"] 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 (jobs) are provided by the OS distribution. [IMPORTANT] ==== 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 various types of system services (+systemd+, +upstart+, and +lsb+), Pacemaker supports a special +service+ 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 init script . a Systemd unit file . an Upstart job === STONITH === indexterm:[Resource,STONITH] indexterm:[STONITH,Resources] The STONITH class is used exclusively for fencing-related resources. This is discussed later in <>. === Nagios Plugins === indexterm:[Resource,Nagios Plugins] indexterm:[Nagios Plugins,Resources] Nagios Plugins footnote:[The project has two independent forks, hosted at https://www.nagios-plugins.org/ and https://www.monitoring-plugins.org/. Output from both projects' plugins is similar, so plugins from either project can be used with pacemaker.] allow us to monitor services on remote hosts. Pacemaker is able to do remote monitoring with the plugins _if they are present_. A common use case is to configure them as resources belonging to a resource container (usually a virtual machine), and the container will be restarted if any of them has failed. Another use is to configure them as ordinary resources to be used for monitoring hosts or services via the network. The supported parameters are same as the long options of the plugin. [[primitive-resource]] == Resource Properties == These values tell the cluster which resource agent to use for the resource, where to find that resource agent 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 resource agent conforms to. Allowed values: +lsb+, +nagios+, +ocf+, +service+, +stonith+, +systemd+, +upstart+ indexterm:[class,Resource] indexterm:[Resource,Property,class] |type |The name of the Resource Agent you wish to use. E.g. +IPaddr+ or +Filesystem+ indexterm:[type,Resource] indexterm:[Resource,Property,type] |provider |The OCF spec allows multiple vendors to supply the same resource agent. To use the OCF resource agents supplied by the Heartbeat project, you would specify +heartbeat+ here. indexterm:[provider,Resource] indexterm:[Resource,Property,provider] |========================================================= The XML definition of a resource can be queried with the `crm_resource` tool. For example: ---- # crm_resource --resource Email --query-xml ---- might produce: .A system resource definition ===== [source,XML] ===== [NOTE] ===== One of the main drawbacks to system services (LSB, systemd or Upstart) resources is that they do not allow any parameters! ===== //// See https://tools.ietf.org/html/rfc5737 for choice of example IP address //// .An OCF resource definition ===== [source,XML] ------- ------- ===== [[s-resource-options]] == Resource Options == Resources have two types of options: 'meta-attributes' and 'instance attributes'. Meta-attributes apply to any type of resource, while instance attributes are specific to each resource agent. === Resource Meta-Attributes === Meta-attributes are used by the cluster to decide how a resource should behave and can be easily set using the `--meta` option of the `crm_resource` command. .Meta-attributes of a Primitive Resource [width="95%",cols="2m,2,<5",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 a|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 (and in the case of <>, promoted to master if appropriate) * +Slave:+ Allow the resource to be started, but only in Slave mode if the resource is <> * +Master:+ Equivalent to +Started+ 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 -|value of +resource-stickiness+ in the +rsc_defaults+ section -|How much does the resource prefer to stay where it is? +|1 for individual clone instances, 0 for all other resources +|A score that will be added to the current node when a resource is already + active. This allows running resources to stay where they are, even if + they would be placed elsewhere if they were being started from a stopped + state. indexterm:[resource-stickiness,Resource Option] indexterm:[Resource,Option,resource-stickiness] |requires |+quorum+ for resources with a +class+ of +stonith+, otherwise +unfencing+ if unfencing is active in the cluster, otherwise +fencing+ if +stonith-enabled+ is true, otherwise +quorum+ a|Conditions under which the resource can be started Allowed 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 <> * +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 fenced _and_ only on nodes that have been <> indexterm:[requires,Resource Option] indexterm:[Resource,Option,requires] |migration-threshold |INFINITY |How many failures may occur for this resource on a node, before this node is marked ineligible to host this resource. A value of 0 indicates that this feature is disabled (the node will never be marked ineligible); by constrast, the cluster treats INFINITY (the default) as a very large but finite number. This option has an effect only if the failed operation specifies +on-fail+ as +restart+ (the default), and additionally for failed +start+ operations, if the cluster property +start-failure-is-fatal+ is +false+. indexterm:[migration-threshold,Resource Option] indexterm:[Resource,Option,migration-threshold] |failure-timeout |0 |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. A value of 0 indicates that this feature is disabled. As with any time-based actions, this is not guaranteed to be checked more frequently than the value of +cluster-recheck-interval+ (see <>). indexterm:[failure-timeout,Resource Option] indexterm:[Resource,Option,failure-timeout] |multiple-active |stop_start a|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] |allow-migrate |TRUE for ocf:pacemaker:remote resources, FALSE otherwise |Whether the cluster should try to "live migrate" this resource when it needs to be moved (see <>) |container-attribute-target | |Specific to bundle resources; see <> |remote-node | |The name of the Pacemaker Remote guest node this resource is associated with, if any. If specified, this both enables the resource as a guest node and defines the unique name used to identify the guest node. The guest must be configured to run the Pacemaker Remote daemon when it is started. +WARNING:+ This value cannot overlap with any resource or node IDs. |remote-port |3121 |If +remote-node+ is specified, the port on the guest used for its Pacemaker Remote connection. The Pacemaker Remote daemon on the guest must be configured to listen on this port. |remote-addr |value of +remote-node+ |If +remote-node+ is specified, the IP address or hostname used to connect to the guest via Pacemaker Remote. The Pacemaker Remote daemon on the guest must be configured to accept connections on this address. |remote-connect-timeout |60s |If +remote-node+ is specified, how long before a pending guest connection will time out. |========================================================= As an example of setting resource options, if you performed the following commands on an LSB Email resource: ------- # crm_resource --meta --resource Email --set-parameter priority --parameter-value 100 # crm_resource -m -r Email -p multiple-active -v block ------- the resulting resource definition might be: .An LSB resource with cluster options ===== [source,XML] ------- ------- ===== +In addition to the cluster-defined meta-attributes described above, you may +also configure arbitrary meta-attributes of your own choosing. Most commonly, +this would be done for use in <>. For example, an IT department +might define a custom meta-attribute to indicate which company department each +resource is intended for. To reduce the chance of name collisions with +cluster-defined meta-attributes added in the future, it is recommended to use +a unique, organization-specific prefix for such attributes. + [[s-resource-defaults]] === Setting Global Defaults for Resource Meta-Attributes === To set a default value for a resource option, add it to the +rsc_defaults+ section with `crm_attribute`. For example, ---- # crm_attribute --type rsc_defaults --name is-managed --update 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 by having their +is-managed+ set to +true+). === Resource Instance Attributes === The resource agents of some resource classes (lsb, systemd and upstart 'not' among 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 example, ---- # crm_resource --resource Public-IP --set-parameter ip --parameter-value 192.0.2.2 ---- 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 +192.0.2.2+. The list of instance attributes supported by an OCF resource agent can be found by calling the resource agent 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 ===== ---- # 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. NB: Please pay attention to the timeouts specified in the actions section below. They should be meaningful for the kind of resource the agent manages. They should be the minimum advised timeouts, but they shouldn't/cannot cover _all_ possible resource instances. So, try to be neither overly generous nor too stingy, but moderate. The minimum timeouts should never be below 10 seconds. Example stateless resource agent Location to store the resource state in. State file Fake attribute that can be changed to cause a reload Fake attribute that can be changed to cause a reload Number of seconds to sleep during operations. This can be used to test how the cluster reacts to operation timeouts. Operation sleep duration in seconds. ------- ===== == Resource Operations == indexterm:[Resource,Action] 'Operations' are actions the cluster can perform on a resource by calling the resource agent. Resource agents must support certain common operations such as -start, stop and monitor, and may implement any others. +start, stop, and monitor, and may implement any others. -Some operations are generated by the cluster itself, for example, stopping and -starting resources as needed. +Operations may be explicitly configured for two purposes: to override defaults +for options (such as timeout) that the cluster will use whenever it initiates +the operation, and to run an operation on a recurring basis (for example, to +monitor the resource for failure). -You can configure operations in the cluster configuration. As an example, by -default the cluster will 'not' ensure your resources stay healthy once they are -started. footnote:[Currently, anyway. Automatic monitoring operations may be -added in a future version of Pacemaker.] 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 +.An OCF resource with a non-default start timeout ===== [source,XML] ------- - + ------- ===== +Pacemaker identifies operations by a combination of name and interval, so this +combination must be unique for each resource. That is, you should not configure +two operations for the same resource with the same name and interval. + .Properties of an Operation [width="95%",cols="2m,3,<6",options="header",align="center"] |========================================================= |Field |Default |Description |id | |A unique name for the operation. indexterm:[id,Action Property] indexterm:[Action,Property,id] |name | |The action to perform. This can be any action supported by the agent; common values include +monitor+, +start+, and +stop+. indexterm:[name,Action Property] indexterm:[Action,Property,name] |interval |0 -|How frequently (in seconds) to perform the operation. A value of 0 means never. - A positive value defines a 'recurring action', which is typically used with - <>. +|How frequently (in seconds) to perform the operation. A value of 0 means "when + needed". A positive value defines a 'recurring action', which is typically + used with <>. 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 |restart '(except for +stop+ operations, which default to' fence 'when STONITH is enabled and' block 'otherwise)' a|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. indexterm:[on-fail,Action Property] indexterm:[Action,Property,on-fail] |enabled |TRUE |If +false+, ignore this operation definition. This is typically used to pause a particular recurring +monitor+ operation; for instance, it can complement the respective resource being unmanaged (+is-managed=false+), as this alone will <>. Disabling the operation does not suppress all actions of the given type. Allowed values: +true+, +false+. indexterm:[enabled,Action Property] indexterm:[Action,Property,enabled] |record-pending |FALSE |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). + This is best set as an _operation default_ (see <>). Allowed values: +true+, +false+. indexterm:[enabled,Action Property] indexterm:[Action,Property,enabled] |role | |Run the operation only on node(s) that the cluster thinks should be in the specified role. This only makes sense for recurring +monitor+ operations. Allowed (case-sensitive) values: +Stopped+, +Started+, and in the case of <>, +Slave+ and +Master+. indexterm:[role,Action Property] indexterm:[Action,Property,role] |========================================================= [[s-resource-monitoring]] === Monitoring Resources for Failure === When Pacemaker first starts a resource, it runs one-time +monitor+ operations (referred to as 'probes') to ensure the resource is running where it's supposed to be, and not running where it's not supposed to be. (This behavior can be affected by the +resource-discovery+ location constraint property.) -Other than those initial probes, Pacemaker will not (by default) check that -the resource continues to stay healthy. As in the example above, you must -configure +monitor+ operations explicitly to perform these checks. +Other than those initial probes, Pacemaker will 'not' (by default) check that +the resource continues to stay healthy. +footnote:[Currently, anyway. Automatic monitoring operations may be +added in a future version of Pacemaker.] +You must configure +monitor+ operations explicitly to perform these checks. + +.An OCF resource with a recurring health check +===== +[source,XML] +------- + + + + + + + + + +------- +===== By default, a +monitor+ operation will ensure that the resource is running where it is supposed to. The +target-role+ property can be used for further checking. For example, if a resource has one +monitor+ operation with +interval=10 role=Started+ and a second +monitor+ operation with +interval=11 role=Stopped+, the cluster will run the first monitor on any nodes it thinks 'should' be running the resource, and the second monitor on any nodes that it thinks 'should not' be running the resource (for the truly paranoid, who want to know when an administrator manually starts a service by mistake). +[NOTE] +==== +Currently, monitors with +role=Stopped+ are not implemented for +<> resources. +==== + [[s-monitoring-unmanaged]] === Monitoring Resources When Administration is Disabled === Recurring +monitor+ operations behave differently under various administrative settings: * When a resource is unmanaged (by setting +is-managed=false+): No monitors will be stopped. + If the unmanaged resource is stopped on a node where the cluster thinks it should be running, the cluster will detect and report that it is not, but it will not consider the monitor failed, and will not try to start the resource until it is managed again. + Starting the unmanaged resource on a different node is strongly discouraged and will at least cause the cluster to consider the resource failed, and may require the resource's +target-role+ to be set to +Stopped+ then +Started+ to be recovered. * When a node is put into standby: All resources will be moved away from the node, and all +monitor+ operations will be stopped on the node, except those - specifying +role+ as +Stopped+. Such rather atypical monitoring will - consequently be started on the node if appropriate. + specifying +role+ as +Stopped+ (which will be newly initiated if + appropriate). * When the cluster is put into maintenance mode: All resources will be marked - as unmanaged. All monitor operations will be stopped, except those with - specifying +role+ as +Stopped+. As with single unmanaged resources, starting + as unmanaged. All monitor operations will be stopped, except those + specifying +role+ as +Stopped+ (which will be newly initiated if + appropriate). As with single unmanaged resources, starting a resource on a node other than where the cluster expects it to be will cause problems. [[s-operation-defaults]] === Setting Global Defaults for Operations === You can change the global default values for operation properties in a given cluster. These are defined in an +op_defaults+ section of the CIB's +configuration+ section, and can be set with `crm_attribute`. For example, ---- # crm_attribute --type op_defaults --name timeout --update 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 for that operation instead. === When Implicit Operations Take a Long Time === The cluster will always perform a number of implicit operations: +start+, +stop+ and a non-recurring +monitor+ operation used at startup to check whether the resource is already active. If one of these is taking too long, then you can create an entry for them and specify a longer timeout. .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. 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: ---- # cibadmin --modify --xml-text '' ---- Once you've done whatever you needed to do, you can then re-enable it with ---- # cibadmin --modify --xml-text '' ---- diff --git a/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt b/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt index c0d1883b04..a7569d1412 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt @@ -1,373 +1,376 @@ :compat-mode: legacy = Reusing Parts of the Configuration = Pacemaker provides multiple ways to simplify the configuration XML by reusing parts of it in multiple places. Besides simplifying the XML, this also allows you to manipulate multiple configuration elements with a single reference. == Reusing Resource Definitions == 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 syntax similar to that of primitives. .Resource template for a migratable Xen virtual machine ==== [source,XML] ---- ---- ==== Once you define a resource template, you can use it in primitives by specifying the +template+ property. .Xen primitive resource using a resource template ==== [source,XML] ---- ---- ==== In the example above, the new primitive +vm1+ will inherit everything from +vm-template+. For example, the equivalent of the above two examples would be: .Equivalent Xen primitive resource not using a resource template ==== [source,XML] ---- ---- ==== If you want to overwrite some attributes or operations, add them to the particular primitive's definition. .Xen resource overriding template values ==== [source,XML] ---- ---- ==== In the example above, the new primitive +vm2+ has special attribute values. Its +monitor+ operation has a longer +timeout+ and +interval+, and the primitive has an additional +stop+ operation. To see the resulting definition of a resource, run: ---- # crm_resource --query-xml --resource vm2 ---- To see the raw definition of a resource in the CIB, run: ---- # crm_resource --query-xml-raw --resource vm2 ---- === Using Templates in Constraints === A resource template can be referenced in the following types of constraints: - +order+ constraints (see <>) - +colocation+ constraints (see <>) - +rsc_ticket+ constraints (for multi-site clusters as described in <>) 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, given the example templates earlier in this chapter: [source,XML] would colocate all VMs with +base-rsc+ and 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`; the other reference must be a regular resource. ====== === Using Templates in Resource Sets === Resource templates can also be referenced in resource sets. For example, given the example templates earlier in this section, then: [source,XML] ---- ---- is the equivalent of the following constraint using a sequential resource set: [source,XML] ---- ---- Or, if the resources referencing the template can run in parallel, then: [source,XML] ---- ---- is the equivalent of the following constraint configuration: [source,XML] ---- ---- [[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] ------- ------- ===== ++id-ref+ can similarly be used with +resource_set+ (in any constraint type), ++nvpair+, and +operations+. + == Tagging Configuration Elements == Pacemaker allows you to 'tag' any configuration element that has an XML ID. The main purpose of tagging is to support higher-level user interface tools; Pacemaker itself only uses tags within constraints. Therefore, what you can do with tags mostly depends on the tools you use. === Configuring Tags === A tag is simply a named list of XML IDs. .Tag referencing three resources ==== [source,XML] ---- ---- ==== What you can do with this new tag depends on what your higher-level tools support. For example, a tool might allow you to enable or disable all of the tagged resources at once, or show the status of just the tagged resources. A single configuration element can be listed in any number of tags. === Using Tags in Constraints and Resource Sets === Pacemaker itself only uses tags in constraints. If you supply a tag name instead of a resource name in any constraint, the constraint will apply to all resources listed in that tag. .Constraint using a tag ==== [source,XML] ---- ---- ==== In the example above, assuming the +all-vms+ tag is defined as in the previous example, the constraint will behave the same as: .Equivalent constraints without tags ==== [source,XML] ---- ---- ==== A tag may be used directly in the constraint, or indirectly by being listed in a <> used in the constraint. When used in a resource set, an expanded tag will honor the set's +sequential+ property. diff --git a/doc/Pacemaker_Explained/en-US/Revision_History.xml b/doc/Pacemaker_Explained/en-US/Revision_History.xml index 839f62c750..3da97ac9b8 100644 --- a/doc/Pacemaker_Explained/en-US/Revision_History.xml +++ b/doc/Pacemaker_Explained/en-US/Revision_History.xml @@ -1,144 +1,159 @@ Revision History 1-0 19 Oct 2009 AndrewBeekhofandrew@beekhof.net Import from Pages.app 2-0 26 Oct 2009 AndrewBeekhofandrew@beekhof.net Cleanup and reformatting of docbook xml complete 3-0 Tue Nov 12 2009 AndrewBeekhofandrew@beekhof.net Split book into chapters and pass validation Re-organize book for use with Publican 4-0 Mon Oct 8 2012 AndrewBeekhofandrew@beekhof.net - Converted to asciidoc - (which is converted to docbook for use with - Publican) - + Converted to asciidoc + (which is converted to docbook for use with + Publican) + 5-0 Mon Feb 23 2015 KenGaillotkgaillot@redhat.com - Update for clarity, stylistic consistency and current command-line syntax - + Update for clarity, stylistic consistency and current command-line syntax + 6-0 Tue Dec 8 2015 KenGaillotkgaillot@redhat.com - Update for Pacemaker 1.1.14 - + Update for Pacemaker 1.1.14 + 7-0 Tue May 3 2016 KenGaillotkgaillot@redhat.com - Update for Pacemaker 1.1.15 - + Update for Pacemaker 1.1.15 + 7-1 Fri Oct 28 2016 KenGaillotkgaillot@redhat.com - Overhaul upgrade documentation, and document node health strategies - + Overhaul upgrade documentation, and document node health strategies + 8-0 Tue Oct 25 2016 KenGaillotkgaillot@redhat.com - Update for Pacemaker 1.1.16 - + Update for Pacemaker 1.1.16 + 9-0 Tue Jul 11 2017 KenGaillotkgaillot@redhat.com - Update for Pacemaker 1.1.17 - + Update for Pacemaker 1.1.17 + 10-0 Fri Oct 6 2017 KenGaillotkgaillot@redhat.com - Update for Pacemaker 1.1.18 - + Update for Pacemaker 1.1.18 + 11-0 Fri Jan 12 2018 KenGaillotkgaillot@redhat.com - Update for Pacemaker 2.0.0 - + Update for Pacemaker 2.0.0 + + + + + + 12-0 + Fri Dec 7 2018 + KenGaillotkgaillot@redhat.com + ReidWahlnwahl@redhat.com + JanPokornýjpokorny@redhat.com + + + + Update for Pacemaker 2.0.1, remove "Further Reading" and "FAQ" sections, + and add minor clarifications and reformatting +