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.
Pacemaker supports several classes of agents:
The OCF standard [1] is basically an extension of the Linux Standard Base conventions for init scripts to:
OCF specs have strict definitions of the exit codes that actions must return [2].
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 reference [http://www.linux-ha.org/wiki/OCF_Resource_Agents] and the Resource Agents chapter of Pacemaker Administration.
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. In order to be used with a Pacemaker cluster, they must conform to the LSB specification [3].
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:
Important
Remember to make sure the computer is not configured to start any services at boot time – that should be controlled by the cluster.
Most Linux distributions have replaced the old SysV [http://en.wikipedia.org/wiki/Init#SysV-style] style of initialization daemons and scripts with Systemd [http://www.freedesktop.org/wiki/Software/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 [4].
Important
Remember to make sure the computer is not configured to start any services at boot time – that should be controlled by the cluster.
Some distributions replaced the old SysV [http://en.wikipedia.org/wiki/Init#SysV-style] style of initialization daemons (and scripts) with Upstart [http://upstart.ubuntu.com/].
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.
Warning
Upstart support is deprecated in Pacemaker. Upstart is no longer an actively maintained project, and test platforms for it are no longer readily usable. Support will likely be dropped entirely at the next major release of Pacemaker.
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:
The STONITH class is used exclusively for fencing-related resources. This is discussed later in Fencing.
Nagios Plugins [5] 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.
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.
| Field | Description |
|---|---|
| id | Your name for the resource |
| class | The standard the resource agent conforms to. Allowed values: lsb, nagios, ocf, service, stonith, systemd, upstart |
| type | The name of the Resource Agent you wish to use. E.g. IPaddr or Filesystem |
| 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. |
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
<primitive id="Email" class="service" type="exim"/>
Note
One of the main drawbacks to system services (LSB, systemd or Upstart) resources is that they do not allow any parameters!
An OCF resource definition
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<instance_attributes id="Public-IP-params">
<nvpair id="Public-IP-ip" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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.
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.
| 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. |
| critical | true | Use this value as the default for influence in all colocation constraints involving this resource, as well as the implicit colocation constraints created if this resource is in a group. For details, see Colocation Influence. |
| target-role | Started | What state should the cluster attempt to keep this resource in? Allowed values:
|
| is-managed | TRUE | Is the cluster allowed to start and stop the resource? Allowed values: true, false |
| maintenance | FALSE | Similar to the maintenance-mode cluster option, but for a single resource. If true, the resource will not be started, stopped, or monitored on any node. This differs from is-managed in that monitors will not be run. Allowed values: true, false |
| resource-stickiness | 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. |
| 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 | Conditions under which the resource can be started. Allowed values:
|
| 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. |
| 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. |
| multiple-active | stop_start | What should the cluster do if it ever finds the resource active on more than one node? Allowed values:
|
| 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 Migrating Resources) |
| container-attribute-target | Specific to bundle resources; see Bundle Node Attributes | |
| 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
<primitive id="Email" class="lsb" type="exim">
<meta_attributes id="Email-meta_attributes">
<nvpair id="Email-meta_attributes-priority" name="priority" value="100"/>
<nvpair id="Email-meta_attributes-multiple-active" name="multiple-active" value="block"/>
</meta_attributes>
</primitive>
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 rules. 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.
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).
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
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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
<?xml version="1.0"?>
<!DOCTYPE resource-agent SYSTEM "ra-api-1.dtd">
<resource-agent name="Dummy" version="2.0">
<version>1.1</version>
<longdesc lang="en">
This is a dummy OCF resource agent. It does absolutely nothing except keep track
of whether it is running or not, and can be configured so that actions fail or
take a long time. Its purpose is primarily for testing, and to serve as a
template for resource agent writers.
</longdesc>
<shortdesc lang="en">Example stateless resource agent</shortdesc>
<parameters>
<parameter name="state" unique-group="state">
<longdesc lang="en">
Location to store the resource state in.
</longdesc>
<shortdesc lang="en">State file</shortdesc>
<content type="string" default="/var/run/Dummy-RESOURCE_ID.state" />
</parameter>
<parameter name="passwd" reloadable="1">
<longdesc lang="en">
Fake password field
</longdesc>
<shortdesc lang="en">Password</shortdesc>
<content type="string" default="" />
</parameter>
<parameter name="fake" reloadable="1">
<longdesc lang="en">
Fake attribute that can be changed to cause a reload
</longdesc>
<shortdesc lang="en">Fake attribute that can be changed to cause a reload</shortdesc>
<content type="string" default="dummy" />
</parameter>
<parameter name="op_sleep" reloadable="1">
<longdesc lang="en">
Number of seconds to sleep during operations. This can be used to test how
the cluster reacts to operation timeouts.
</longdesc>
<shortdesc lang="en">Operation sleep duration in seconds.</shortdesc>
<content type="string" default="0" />
</parameter>
<parameter name="fail_start_on" reloadable="1">
<longdesc lang="en">
Start, migrate_from, and reload-agent actions will return failure if running on
the host specified here, but the resource will run successfully anyway (future
monitor calls will find it running). This can be used to test on-fail=ignore.
</longdesc>
<shortdesc lang="en">Report bogus start failure on specified host</shortdesc>
<content type="string" default="" />
</parameter>
<parameter name="envfile" reloadable="1">
<longdesc lang="en">
If this is set, the environment will be dumped to this file for every call.
</longdesc>
<shortdesc lang="en">Environment dump file</shortdesc>
<content type="string" default="" />
</parameter>
</parameters>
<actions>
<action name="start" timeout="20s" />
<action name="stop" timeout="20s" />
<action name="monitor" timeout="20s" interval="10s" depth="0"/>
<action name="reload" timeout="20s" />
<action name="reload-agent" timeout="20s" />
<action name="migrate_to" timeout="20s" />
<action name="migrate_from" timeout="20s" />
<action name="validate-all" timeout="20s" />
<action name="meta-data" timeout="5s" />
</actions>
</resource-agent>
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.
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).
An OCF resource with a non-default start timeout
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<operations>
<op id="Public-IP-start" name="start" timeout="60s"/>
</operations>
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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.
Operation properties may be specified directly in the op element as XML attributes, or in a separate meta_attributes block as nvpair elements. XML attributes take precedence over nvpair elements if both are specified.
| Field | Default | Description |
|---|---|---|
| id | A unique name for the operation. |
|
| name | The action to perform. This can be any action supported by the agent; common values include monitor, start, and stop. |
|
| interval | 0 | 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 monitor. |
| timeout | How long to wait before declaring the action has failed |
|
| on-fail | Varies by action:
|
The action to take if this action ever fails. Allowed values:
|
| 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 not block any configured monitoring. Disabling the operation does not suppress all actions of the given type. Allowed values: true, false. |
| record-pending | TRUE | 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 Setting Global Defaults for Operations). Allowed values: true, false. |
| 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 promotable clone resources, Unpromoted and Promoted. |
Note
When on-fail is set to demote, recovery from failure by a successful demote causes the cluster to recalculate whether and where a new instance should be promoted. The node with the failure is eligible, so if promotion scores have not changed, it will be promoted again.
There is no direct equivalent of migration-threshold for the promoted role, but the same effect can be achieved with a location constraint using a rule with a node attribute expression for the resource’s fail count.
For example, to immediately ban the promoted role from a node with any failed promote or promoted instance monitor:
<rsc_location id="loc1" rsc="my_primitive">
<rule id="rule1" score="-INFINITY" role="Promoted" boolean-op="or">
<expression id="expr1" attribute="fail-count-my_primitive#promote_0"
operation="gte" value="1"/>
<expression id="expr2" attribute="fail-count-my_primitive#monitor_10000"
operation="gte" value="1"/>
</rule>
</rsc_location>
This example assumes that there is a promotable clone of the my_primitive resource (note that the primitive name, not the clone name, is used in the rule), and that there is a recurring 10-second-interval monitor configured for the promoted role (fail count attributes specify the interval in milliseconds).
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 [6]. You must configure monitor operations explicitly to perform these checks.
An OCF resource with a recurring health check
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<operations>
<op id="Public-IP-start" name="start" timeout="60s"/>
<op id="Public-IP-monitor" name="monitor" interval="60s"/>
</operations>
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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 clone resources.
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 (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 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.
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.
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
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<operations>
<op id="public-ip-startup" name="monitor" interval="0" timeout="90s"/>
<op id="public-ip-start" name="start" interval="0" timeout="180s"/>
<op id="public-ip-stop" name="stop" interval="0" timeout="15min"/>
</operations>
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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.
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<operations>
<op id="public-ip-health-60" name="monitor" interval="60">
<instance_attributes id="params-public-ip-depth-60">
<nvpair id="public-ip-depth-60" name="OCF_CHECK_LEVEL" value="10"/>
</instance_attributes>
</op>
<op id="public-ip-health-300" name="monitor" interval="300">
<instance_attributes id="params-public-ip-depth-300">
<nvpair id="public-ip-depth-300" name="OCF_CHECK_LEVEL" value="20"/>
</instance_attributes>
</op>
</operations>
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-level" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
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
<primitive id="Public-IP" class="ocf" type="IPaddr" provider="heartbeat">
<operations>
<op id="public-ip-check" name="monitor" interval="60s" enabled="false"/>
</operations>
<instance_attributes id="params-public-ip">
<nvpair id="public-ip-addr" name="ip" value="192.0.2.2"/>
</instance_attributes>
</primitive>
This can be achieved from the command line by executing:
# cibadmin --modify --xml-text '<op id="public-ip-check" enabled="false"/>'
Once you’ve done whatever you needed to do, you can then re-enable it with
# cibadmin --modify --xml-text '<op id="public-ip-check" enabled="true"/>'
| [1] | See https://github.com/ClusterLabs/OCF-spec/tree/master/ra. The Pacemaker implementation has been somewhat extended from the OCF specs. |
| [2] | The resource-agents source code includes the ocf-tester script, which can be useful in this regard. |
| [3] | 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. |
| [4] | For example, http://0pointer.de/blog/projects/systemd-for-admins-3.html |
| [5] | 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. |
| [6] | Currently, anyway. Automatic monitoring operations may be added in a future version of Pacemaker. |