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Chapter 10. Configuring cluster resources

A cluster resource is an instance of a program, an application, or data to be managed by the cluster service. These resources are abstracted by agents that provide a standard interface for managing the resource in a cluster environment.

To ensure that resources remain healthy, you can add a monitoring operation to a resource’s definition. If you do not specify a monitoring operation for a resource, one is added by default. You can determine the behavior of a resource in a cluster by configuring constraints for that resource. You can configure the following categories of constraints:

As a shorthand for configuring a set of constraints that will locate a set of resources together and ensure that the resources start sequentially and stop in reverse order, Pacemaker supports the concept of resource groups. After you have created a resource group, you can configure constraints on the group itself just as you configure constraints for individual resources. For information about configuring resource groups, see Configuring resource groups.

The format for the command to create a cluster resource is as follows: 

pcs resource create resource_id [standard:[provider:]]type [resource_options] [op operation_action operation_options [operation_action operation options]...] [meta meta_options...] [clone [clone_id] [clone_options] | promotable [clone_id] [clone_options] [--wait[=n]]
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Key cluster resource creation options include the following:

  • The --before and --after options specify the position of the added resource relative to a resource that already exists in a resource group.
  • Specifying the --disabled option indicates that the resource is not started automatically.

There is no limit to the number of resources you can create in a cluster.

Resource creation examples

The following command creates a resource with the name VirtualIP of standard ocf, provider heartbeat, and type IPaddr2. The floating address of this resource is 192.168.0.120, and the system will check whether the resource is running every 30 seconds. For information about resource standards and providers, see Resource agent identifiers. 

# pcs resource create VirtualIP ocf:heartbeat:IPaddr2 ip=192.168.0.120 cidr_netmask=24 op monitor interval=30s
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Alternately, you can omit the standard and provider fields and use the following command. This will default to a standard of ocf and a provider of heartbeat. 

# pcs resource create VirtualIP IPaddr2 ip=192.168.0.120 cidr_netmask=24 op monitor interval=30s
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Deleting a configured resource

Delete a configured resource with the following command. 

pcs resource delete resource_id
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For example, the following command deletes an existing resource with a resource ID of VirtualIP. 

# pcs resource delete VirtualIP
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You can delete multiple resources with a single command. The following command deletes an existing resource with a resource ID of resource1 and an existing resource with a resource ID of resource2. 

# pcs resource delete resource1 resource2
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10.1. Resource agent identifiers

The identifiers that you define for a resource tell the cluster which agent to use for the resource, where to find that agent and what standards it conforms to.

The following table describes these properties of a resource agent.

Table 10.1. Resource Agent Identifiers
FieldDescription

standard

The standard the agent conforms to. Allowed values and their meaning:

* ocf - The specified type is the name of an executable file conforming to the Open Cluster Framework Resource Agent API and located beneath /usr/lib/ocf/resource.d/provider

* lsb - The specified type is the name of an executable file conforming to Linux Standard Base Init Script Actions. If the type does not specify a full path, the system will look for it in the /etc/init.d directory.

* systemd - The specified type is the name of an installed systemd unit

* service - Pacemaker will search for the specified type, first as an lsb agent, then as a systemd agent

* nagios - The specified type is the name of an executable file conforming to the Nagios Plugin API and located in the /usr/libexec/nagios/plugins directory, with OCF-style metadata stored separately in the /usr/share/nagios/plugins-metadata directory (available in the nagios-agents-metadata package for certain common plugins).

type

The name of the resource agent you wish to use, for example IPaddr or Filesystem

provider

The OCF spec allows multiple vendors to supply the same resource agent. Most of the agents shipped by Red Hat use heartbeat as the provider.

10.2. Displaying resources and resource parameters

The following table summarizes the resource display commands.

pcs Display CommandOutput

pcs resource describe [standard:[provider:]]type

Displays a description of an individual resource, the parameters you can set for that resource, and the default values for the resource. For example, pcs resource describe ocf:heartbeat:apache displays information for a resource of type apache.

pcs resource status

Displays a list of all configured resources.

pcs resource config resource_id

Displays the configured parameters for a resource.

pcs resource status resource_id

Displays the status of an individual resource.

pcs resource status node=node_id

Displays the status of the resources running on a specific node, use the following command. You can use this command to display the status of resources on both cluster and remote nodes.

pcs resource list

Displays a list of all available resources.

pcs resource standards

Displays a list of available resource agent standards.

pcs resource providers

Displays a list of available resource agent providers.

pcs resource list string

Displays a list of available resources filtered by the specified string. You can use this command to display resources filtered by the name of a standard, a provider, or a type.

10.3. Configuring resource meta options

In addition to the resource-specific parameters, you can configure additional resource options for any resource. These options are used by the cluster to decide how your resource should behave.

The following table describes the resource meta options.

Table 10.2. Resource Meta Options
FieldDefaultDescription

priority

0

If not all resources can be active, the cluster will stop lower priority resources in order to keep higher priority ones active.

target-role

Started

Indicates what state the cluster should 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 promotable clones, promoted if appropriate)

* Promoted - Allow the resource to be started and, if appropriate, promoted

* Unpromoted - Allow the resource to be started, but only in unpromoted mode if the resource is promotable

is-managed

true

Indicates whether the cluster is allowed to start and stop the resource. Allowed values: true, false

resource-stickiness

1

Value to indicate how much the resource prefers to stay where it is.

requires

Calculated

Indicates under what conditions the resource can be started.

Defaults to fencing except under the conditions noted below. Possible values:

* nothing - The cluster can always start the resource.

* quorum - The cluster can only start this resource if a majority of the configured nodes are active. This is the default value if stonith-enabled is false or the resource’s standard is stonith.

* 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 fenced.

* 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 unfenced. This is the default value if the provides=unfencing stonith meta option has been set for a fencing device.

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 contrast, the cluster treats INFINITY (the default) as a very large but finite number. This option has an effect only if the failed operation has on-fail=restart (the default), and additionally for failed start operations if the cluster property start-failure-is-fatal is false.

failure-timeout

0 (disabled)

Used in conjunction with the migration-threshold option, indicates 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.

multiple-active

stop_start

Indicates what the cluster should 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

* stop_unexpected - stop only unexpected instances of the resource, without requiring a full restart. It is the user’s responsibility to verify that the service and its resource agent can function with extra active instances without requiring a full restart.

critical

true

Sets the default value for the influence option for all colocation constraints involving the resource as a dependent resource (target_resource), including implicit colocation constraints created when the resource is part of a resource group. The influence colocation constraint option determines whether the cluster will move both the primary and dependent resources to another node when the dependent resource reaches its migration threshold for failure, or whether the cluster will leave the dependent resource offline without causing a service switch. The critical resource meta option can have a value of true or false, with a default value of true.

allow-unhealthy-nodes

false

When set to true, the resource is not forced off a node due to degraded node health. When health resources have this attribute set, the cluster can automatically detect if the node’s health recovers and move resources back to it. A node’s health is determined by a combination of the health attributes set by health resource agents based on local conditions, and the strategy-related options that determine how the cluster reacts to those conditions.

10.3.1. Setting meta options

You can set a resource option for a particular resource to a value other than the default when you create the resource. You can also set the value of a resource meta option for an existing resource, group, or cloned resource.

The following procedure provides example commands that set the value of resource meta options both on resource creation and on an existing resource.

Procedure

  1. Create a resource with a resource-stickiness value of 50. 

    # pcs resource create VirtualIP ocf:heartbeat:IPaddr2 ip=192.168.0.120 meta resource-stickiness=50
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  2. For the existing resource named dummy_resource, set the failure-timeout meta option to 20 seconds, so that the resource can attempt to restart on the same node in 20 seconds. 

    # pcs resource meta dummy_resource failure-timeout=20s
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  3. Display the values for the resource to verify that failure-timeout=20s is set. 

    # pcs resource config dummy_resource
 Resource: dummy_resource (class=ocf provider=heartbeat type=Dummy)
  Meta Attrs: failure-timeout=20s
  ...
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10.3.2. Changing the default value of a resource option

You can change the default value of a resource option for all resources with the pcs resource defaults update command. The following command resets the default value of resource-stickiness to 100. 

# pcs resource defaults update resource-stickiness=100
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The original pcs resource defaults name=value command, which set defaults for all resources in previous releases, remains supported unless there is more than one set of defaults configured. However, pcs resource defaults update is now the preferred version of the command.

10.3.3. Changing the default value of a resource option for sets of resources

You can create multiple sets of resource defaults with the pcs resource defaults set create command, which allows you to specify a rule that contains resource expressions. Only resource and date expressions, including and, or and parentheses, are allowed in rules that you specify with this command.

With the pcs resource defaults set create command, you can configure a default resource value for all resources of a particular type. If, for example, you are running databases which take a long time to stop, you can increase the resource-stickiness default value for all resources of the database type to prevent those resources from moving to other nodes more often than you desire.

The following command sets the default value of resource-stickiness to 100 for all resources of type pqsql.

  • The id option, which names the set of resource defaults, is not mandatory. If you do not set this option pcs will generate an ID automatically. Setting this value allows you to provide a more descriptive name.

  • In this example, ::pgsql means a resource of any class, any provider, of type pgsql.

    • Specifying ocf:heartbeat:pgsql would indicate class ocf, provider heartbeat, type pgsql,
    • Specifying ocf:pacemaker: would indicate all resources of class ocf, provider pacemaker, of any type. 
# pcs resource defaults set create id=pgsql-stickiness meta resource-stickiness=100 rule resource ::pgsql
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To change the default values in an existing set, use the pcs resource defaults set update command.

10.3.4. Displaying currently configured resource defaults

The pcs resource defaults [config] command displays a list of currently configured default values for resource options, including any rules that you specified. You can display the output of this command in text, JSON, and command formats.

  • Specifying --output-format=text displays the configured resource defaults in plain text format, which is the default value for this option.
  • Specifying --output-format=cmd displays the pcs resource defaults commands created from the current cluster defaults configuration. You can use these commands to re-create configured resource defaults on a different system.
  • Specifying --output-format=json displays the configured resource defaults in JSON format, which is suitable for machine parsing.

The following example procedure shows the three different output formats of the pcs resource defaults config command after you reset the default values for a resource.

Procedure

  1. Reset the default values for or any ocf:pacemaker:pgsql resource. 

    # pcs resource defaults set create id=set-1 score=100 meta resource-stickiness=10 rule resource ocf:pacemaker:pgsql
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  2. Display the configured resource default values in plain text. 

    # pcs resource defaults config
Meta Attrs: build-resource-defaults
  resource-stickiness=1
Meta Attrs: set-1 score=100
  resource-stickiness=10
  Rule: boolean-op=and score=INFINITY
    Expression: resource ocf:pacemaker:pgsql
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  3. Display the pcs resource defaults commands created from the current cluster defaults configuration. 

    # pcs resource defaults config --output-format=cmd
pcs -- resource defaults set create id=build-resource-defaults \
  meta resource-stickiness=1;
pcs -- resource defaults set create id=set-1 score=100 \
  meta resource-stickiness=10 \
  rule 'resource ocf:pacemaker:pgsql'
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  4. Display the configured resource default values in JSON format. 

    # pcs resource defaults config --output-format=json
{"instance_attributes": [], "meta_attributes": [{"id": "build-resource-defaults", "options": {}, "rule": null, "nvpairs": [{"id": "build-resource-stickiness", "name": "resource-stickiness", "value": "1"}]}, {"id": "set-1", "options": {"score": "100"}, "rule": {"id": "set-1-rule", "type": "RULE", "in_effect": "UNKNOWN", "options": {"boolean-op": "and", "score": "INFINITY"}, "date_spec": null, "duration": null, "expressions": [{"id": "set-1-rule-rsc-ocf-pacemaker-pgsql", "type": "RSC_EXPRESSION", "in_effect": "UNKNOWN", "options": {"class": "ocf", "provider": "pacemaker", "type": "pgsql"}, "date_spec": null, "duration": null, "expressions": [], "as_string": "resource ocf:pacemaker:pgsql"}], "as_string": "resource ocf:pacemaker:pgsql"}, "nvpairs": [{"id": "set-1-resource-stickiness", "name": "resource-stickiness", "value": "10"}]}]}
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10.4. Configuring 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, Pacemaker supports the concept of resource groups.

10.4.1. Creating a resource group

You create a resource group with the following command, specifying the resources to include in the group. If the group does not exist, this command creates the group. If the group exists, this command adds additional resources to the group. The resources will start in the order you specify them with this command, and will stop in the reverse order of their starting order. 

pcs resource group add group_name resource_id [resource_id] ... [resource_id] [--before resource_id | --after resource_id]
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You can use the --before and --after options of this command to specify the position of the added resources relative to a resource that already exists in the group.

You can also add a new resource to an existing group when you create the resource, using the following command. The resource you create is added to the group named group_name. If the group group_name does not exist, it will be created. 

pcs resource create resource_id [standard:[provider:]]type [resource_options] [op operation_action operation_options] --group group_name
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There is no limit to the number of resources a group can contain. The fundamental properties of a group are as follows.

  • Resources are colocated within a group.
  • Resources are started in the order in which you specify them. If a resource in the group cannot run anywhere, then no resource specified after that resource is allowed to run.
  • Resources are stopped in the reverse order in which you specify them.

Additional properties of a group are as follows:

  • You can set the following options for a resource group, and they maintain the same meaning as when they are set for a single resource: priority, target-role, is-managed. For information about resource meta options, see Configuring resource meta options.
  • 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.

The following example creates a resource group named shortcut that contains the existing resources IPaddr and Email. 

# pcs resource group add shortcut IPaddr Email
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In this example:

  • The IPaddr is started first, then Email.
  • The Email resource is stopped first, then IPAddr.
  • If IPaddr cannot run anywhere, neither can Email.
  • If Email cannot run anywhere, however, this does not affect IPaddr.

10.4.2. Removing a resource group

You remove a resource from a group with the following command. If there are no remaining resources in the group, this command removes the group itself. 

pcs resource group remove group_name resource_id...
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10.4.3. Displaying resource groups

The following command lists all currently configured resource groups. 

pcs resource group list
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10.5. Displaying resource dependencies

The following command displays the relations between cluster resources in a tree structure. 

pcs resource relations resource [--full]
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If the --full option is used, the command displays additional information, including the constraint IDs and the resource types.

In the following example, there are 3 configured resources: C, D, and E. 

# pcs constraint order start C then start D
Adding C D (kind: Mandatory) (Options: first-action=start then-action=start)
# pcs constraint order start D then start E
Adding D E (kind: Mandatory) (Options: first-action=start then-action=start)

# pcs resource relations C
C
`- order
   |  start C then start D
   `- D
      `- order
         |  start D then start E
         `- E
# pcs resource relations D
D
|- order
|  |  start C then start D
|  `- C
`- order
   |  start D then start E
   `- E
# pcs resource relations E
E
`- order
   |  start D then start E
   `- D
      `- order
         |  start C then start D
         `- C
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In the following example, there are 2 configured resources: A and B. Resources A and B are part of resource group G. 

# pcs resource relations A
A
`- outer resource
   `- G
      `- inner resource(s)
         |  members: A B
         `- B
# pcs resource relations B
B
`- outer resource
   `- G
      `- inner resource(s)
         |  members: A B
         `- A
# pcs resource relations G
G
`- inner resource(s)
   |  members: A B
   |- A
   `- B
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