diff --git a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.xml b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.xml index fc9b6d0580..0ed6aee091 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.xml +++ b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Resources.xml @@ -1,897 +1,897 @@ Advanced Resource Types
Groups - A Syntactic Shortcut 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. An example group ]]> 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 If Public-IP can’t run anywhere, neither can Email 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 ]]> Obviously as the group grows bigger, the reduced configuration effort can become significant.
Properties Properties of a Group Resource Field Description id Your name for the group
Options Options inherited from simple resources: priority, target-role, is-managed
Using Groups
Instance Attributes Groups have no instance attributes, however any that are set here will be inherited by the group's children.
Contents Groups may only contain a collection of primitive cluster resources. To refer to the child of a group resource, just use the child's id instead of the group's.
Constraints Although it is possible to reference the group's children in constraints, it is usually preferable to use the group's name instead. Example constraints involving groups ]]>
Stickiness Stickiness, the measure of how much a resource wants to stay where it is, is additive in groups. Every active member of the group will contribute its stickiness value to the group's total. So if the default resource-stickiness is 100 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.
Clones - Resources That Should be Active on Multiple Hosts Clones were initially conceived as a convenient way to start N instances of an IP resource and have them distributed throughout the cluster for load balancing. They have turned out to quite useful for a number of purposes including integrating with Red Hat's DLM, the fencing subsystem and OCFS2. You can clone any resource provided the resource agent supports it. Three types of cloned resources exist. Anonymous Globally Unique Stateful Anonymous clones are the simplest type. These resources behave completely identically everywhere they are running. Because of this, there can only be one copy of an anonymous clone active per machine. Globally unique clones are distinct entities. A copy of the clone running on one machine is not equivalent to another instance on another node. Nor would any two copies on the same node be equivalent. Stateful clones are covered later in . An example clone ]]>
Properties Properties of a Clone Resource Field Description id Your name for the clone
Options Options inherited from simple resources: priority, target-role, is-managed Clone specific configuration options Field Description clone-max How many copies of the resource to start. Defaults to the number of nodes in the cluster. clone-node-max How many copies of the resource can be started on a single node. Defaults to 1. notify When stopping or starting a copy of the clone, tell all the other copies beforehand and when the action was successful. Allowed values: true, false globally-unique - Does each copy of the clone perform a different function? Allowed values: true, false + Does each copy of the clone perform a different function? Allowed values: true, false ordered Should the copies be started in series (instead of in parallel). Allowed values: true, false interleave Changes the behavior of ordering constraints (between clones/masters) so that instances can start/stop as soon as their peer instance has (rather than waiting for every instance of the other clone has). Allowed values: true, false
Using Clones
Instance Attributes Clones have no instance attributes, however any that are set here will be inherited by the clone's children.
Contents Clones must contain exactly one group or one regular resource. You should never reference the name of a clone's child. If you think you need to do this, you probably need to re-evaluate your design.
Constraints In most cases, a clone will have a single copy on each active cluster node. However if this is not the case, you can indicate which nodes the cluster should to preferentially assign copies to with resource location constraints. These constraints are written no differently to those for regular resources except that the clone's id is used. Ordering constraints behave slightly differently for clones. In the example below, apache-stats will wait until all copies of the 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 the clone. Colocation of a regular (or group) resource with a clone means that the resource can run on any machine with an active copy of the clone. The cluster will choose a copy based on where the clone is running and the rsc resource's own location preferences. Colocation between clones is also possible. In such cases, the set of allowed locations for the rsc clone is limited to nodes on which the with clone is (or will be) active. Allocation is then performed as-per-normal. Example constraints involving clones ]]>
Stickiness 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.
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. Globally unique clones do require some 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}. Unless of course they are failed, in which case they should return one of the other OCF error codes. Copies of a clone are identified by appending a colon and a numerical offset. Eg. 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 copy it is by examining OCF_RESKEY_CRM_meta_clone. You should not make any assumptions (based on OCF_RESKEY_CRM_meta_clone) about which copies are active. In particular, the list of active copies will not always be an unbroken sequence, nor always start at 0.
Notifications Supporting notifications requires the notify action to be implemented. Once supported, the notify action will be passed 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 Variable Description OCF_RESKEY_CRM_meta_notify_type Allowed values: pre, post OCF_RESKEY_CRM_meta_notify_operation Allowed values: start, stop OCF_RESKEY_CRM_meta_notify_start_resource Resources to be started OCF_RESKEY_CRM_meta_notify_stop_resource Resources to be stopped OCF_RESKEY_CRM_meta_notify_active_resource Resources the that are running OCF_RESKEY_CRM_meta_notify_inactive_resource Resources the that are not running OCF_RESKEY_CRM_meta_notify_start_uname Nodes on which resources will be started OCF_RESKEY_CRM_meta_notify_stop_uname Nodes on which resources will be stopped OCF_RESKEY_CRM_meta_notify_active_uname Nodes on which resources are running OCF_RESKEY_CRM_meta_notify_inactive_uname Nodes on which resources are not running
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. 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 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" Example notification variables
Proper Interpretation of Notification Environment 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
Multi-state - Resources That Have Multiple Modes Multi-state resources are a specialization of Clones (please ensure you understand the section on clones before continuing) that allow the instances to be in one of two operating modes. These modes are called Master and Slave but can mean whatever you wish them to mean. The only limitation is that when an instance is started, it must come up in the Slave state.
Properties Properties of a Multi-State Resource Field Description id Your name for the multi-state resource
Options Options inherited from simple resources: priority, target-role, is-managed Options inherited from clone resources: clone-max, clone-node-max, notify, globally-unique, ordered, interleave Multi-state specific resource configuration options Field Description master-max How many copies of the resource can be promoted to master status. Defaults to 1. master-node-max How many copies of the resource can be promoted to master status on a single node. Defaults to 1.
Using Multi-state Resources
Instance Attributes Multi-state resources have no instance attributes, however any that are set here will be inherited by the master's children.
Contents Masters must contain exactly one group or one regular resource. You should never reference the name of a master's child. If you think you need to do this, you probably need to re-evaluate your design.
Monitoring Multi-State Resources The normal type of monitor actions you define are not sufficient to monitor a multi-state resource in the Master state. To detect failures of the master instance, you need to define an additional monitor action with role="Master". It is crucial that every monitor operation has a different interval Monitoring both states of a multi-state resource ]]>
Constraints In most cases, a multi-state resources will have a single copy on each active cluster node. However if this is not the case, you can indicate which nodes the cluster should to preferentially assign copies to with resource location constraints. These constraints are written no differently to those for regular resources except that the master's id is used. When considering multi-state resources in constraints, for most purposes it is sufficient to treat them as clones. The exception is when the rsc-role and/or with-rsc-role (for colocation constraints) and first-action and/or then-action (for ordering constraints) are used. Additional constraint options relevant to multi-state resources Field Description rsc-role An additional attribute of colocation constraints that specifies the role that rsc must be in. Allowed values: Started, Master, Slave with-rsc-role An additional attribute of colocation constraints that specifies the role that with-rsc must be in. Allowed values: Started, Master, Slave first-action An additional attribute of ordering constraints that specifies the action that the first resource must complete before executing the specified action for the then resource. Allowed values: start, stop, promote, demote then-action An additional attribute of ordering constraints that specifies the action that the then resource can only execute after the first-action on the first resource has completed. Allowed values: start, stop, promote, demote. Defaults to the value (specified or implied) of first-action
In the example below, myApp will wait until one of database copies has been started and promoted to master before being started itself. Only if no copies can be promoted will apache-stats be prevented from being active. Additionally, the database will wait for myApp to be stopped before it is demoted. Colocation of a regular (or group) resource with a multi-state resource means that it can run on any machine with an active copy of the clone that is in the specified state (Master or Slave). In the example, 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 multi-state 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 clone is (or will be) in the specified role. Allocation is then performed as-per-normal. Example constraints involving multi-state resources ]]>
Stickiness 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.
Which Resource Instance is Promoted During the start operation, most Resource Agent scripts should call the crm_master utility. This tool automatically detects both the resource and host and should be used to set a preference for being promoted. Based on this, master-max, and master-node-max, the instance(s) with the highest preference will be promoted. The other alternative is to create a location constraint that indicates which nodes are most preferred as masters. Manually specifying which node should be promoted ]]>
Resource Agent Requirements Since multi-state resources are an extension of cloned resources, all the requirements of Clones are also requirements of multi-state resources. Additionally, multi-state resources require two extra actions demote and promote. These actions 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 then decide which instances to promote into a 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 Monitor Return Code Description OCF_NOT_RUNNING Stopped OCF_SUCCESS Running (Slave) OCF_RUNNING_MASTER Running (Master) OCF_FAILED_MASTER Failed (Master) Other Failed (Slave)
Notifications Like with clones, supporting notifications requires the notify action to be implemented. Once supported, the notify action will be passed 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 Master notify actions <footnote><para>Variables in bold are specific to Master resources and all behave in the same manner as described for Clone resources.</para></footnote> Variable Description OCF_RESKEY_CRM_meta_notify_type Allowed values: pre, post OCF_RESKEY_CRM_meta_notify_operation Allowed values: start, stop OCF_RESKEY_CRM_meta_notify_active_resource Resources the that are running OCF_RESKEY_CRM_meta_notify_inactive_resource Resources the that are not running OCF_RESKEY_CRM_meta_notify_master_resource Resources that are running in Master mode OCF_RESKEY_CRM_meta_notify_slave_resource Resources that are running in Slave mode OCF_RESKEY_CRM_meta_notify_start_resource Resources to be started OCF_RESKEY_CRM_meta_notify_stop_resource Resources to be stopped OCF_RESKEY_CRM_meta_notify_promote_resource Resources to be promoted OCF_RESKEY_CRM_meta_notify_demote_resource Resources to be demoted OCF_RESKEY_CRM_meta_notify_start_uname Nodes on which resources will be started OCF_RESKEY_CRM_meta_notify_stop_uname Nodes on which resources will be stopped OCF_RESKEY_CRM_meta_notify_promote_uname Nodes on which resources will be promoted OCF_RESKEY_CRM_meta_notify_demote_uname Nodes on which resources will be demoted OCF_RESKEY_CRM_meta_notify_active_uname Nodes on which resources are running OCF_RESKEY_CRM_meta_notify_inactive_uname Nodes on which resources are not running OCF_RESKEY_CRM_meta_notify_master_uname Nodes on which resources are running in Master mode OCF_RESKEY_CRM_meta_notify_slave_uname Nodes on which resources are running in Slave mode
Proper Interpretation of Notification Environment 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