4. Configuring Pacemaker

Pacemaker’s configuration, the CIB, is stored in XML format. Cluster administrators have multiple options for modifying the configuration either via the XML, or at a more abstract (and easier for humans to understand) level.

Pacemaker reacts to configuration changes as soon as they are saved. Pacemaker’s command-line tools and most higher-level tools provide the ability to batch changes together and commit them at once, rather than make a series of small changes, which could cause avoid unnecessary actions as Pacemaker responds to each change individually.

Pacemaker tracks revisions to the configuration and will reject any update older than the current revision. Thus, it is a good idea to serialize all changes to the configuration. Avoid attempting simultaneous changes, whether on the same node or different nodes, and whether manually or using some automated configuration tool.

Note

It is not necessary to update the configuration on all cluster nodes. Pacemaker immediately synchronizes changes to all active members of the cluster. To reduce bandwidth, the cluster only broadcasts the incremental updates that result from your changes and uses checksums to ensure that each copy is consistent.

4.1. Configuration Using Higher-level Tools

Most users will benefit from using higher-level tools provided by projects separate from Pacemaker. Some of the most commonly used include the crm shell, hawk, and pcs. [1]

See those projects’ documentation for details on how to configure Pacemaker using them.

4.2. Configuration Using Pacemaker’s Command-Line Tools

Pacemaker provides lower-level, command-line tools to manage the cluster. Most configuration tasks can be performed with these tools, without needing any XML knowledge.

To enable STONITH for example, one could run:

# crm_attribute --name stonith-enabled --update 1

Or, to check whether node1 is allowed to run resources, there is:

# crm_standby --query --node node1

Or, to change the failure threshold of my-test-rsc, one can use:

# crm_resource -r my-test-rsc --set-parameter migration-threshold --parameter-value 3 --meta

Examples of using these tools for specific cases will be given throughout this document where appropriate. See the man pages for further details.

See Edit the CIB XML with cibadmin for how to edit the CIB using XML.

See Batch Configuration Changes with crm_shadow for a way to make a series of changes, then commit them all at once to the live cluster.

4.2.1. Working with CIB Properties

Although these fields can be written to by the user, in most cases the cluster will overwrite any values specified by the user with the “correct” ones.

To change the ones that can be specified by the user, for example admin_epoch, one should use:

# cibadmin --modify --xml-text '<cib admin_epoch="42"/>'

A complete set of CIB properties will look something like this:

XML attributes set for a cib element

<cib crm_feature_set="3.0.7" validate-with="pacemaker-1.2"
   admin_epoch="42" epoch="116" num_updates="1"
   cib-last-written="Mon Jan 12 15:46:39 2015" update-origin="rhel7-1"
   update-client="crm_attribute" have-quorum="1" dc-uuid="1">

4.2.2. Querying and Setting Cluster Options

Cluster options can be queried and modified using the crm_attribute tool. To get the current value of cluster-delay, you can run:

# crm_attribute --query --name cluster-delay

which is more simply written as

# crm_attribute -G -n cluster-delay

If a value is found, you’ll see a result like this:

# crm_attribute -G -n cluster-delay
scope=crm_config name=cluster-delay value=60s

If no value is found, the tool will display an error:

# crm_attribute -G -n clusta-deway
scope=crm_config name=clusta-deway value=(null)
Error performing operation: No such device or address

To use a different value (for example, 30 seconds), simply run:

# crm_attribute --name cluster-delay --update 30s

To go back to the cluster’s default value, you can delete the value, for example:

# crm_attribute --name cluster-delay --delete
Deleted crm_config option: id=cib-bootstrap-options-cluster-delay name=cluster-delay

4.2.3. When Options are Listed More Than Once

If you ever see something like the following, it means that the option you’re modifying is present more than once.

Deleting an option that is listed twice

# crm_attribute --name batch-limit --delete

Please choose from one of the matches below and supply the 'id' with --id
Multiple attributes match name=batch-limit in crm_config:
Value: 50          (set=cib-bootstrap-options, id=cib-bootstrap-options-batch-limit)
Value: 100         (set=custom, id=custom-batch-limit)

In such cases, follow the on-screen instructions to perform the requested action. To determine which value is currently being used by the cluster, refer to the “Rules” chapter of Pacemaker Explained.

4.3. Connecting from a Remote Machine

Provided Pacemaker is installed on a machine, it is possible to connect to the cluster even if the machine itself is not in the same cluster. To do this, one simply sets up a number of environment variables and runs the same commands as when working on a cluster node.

Environment Variables Used to Connect to Remote Instances of the CIB

Environment Variable	Default	Description
CIB_user	$USER	The user to connect as. Needs to be part of the haclient group on the target host.
CIB_passwd		The user’s password. Read from the command line if unset.
CIB_server	localhost	The host to contact
CIB_port		The port on which to contact the server; required.
CIB_encrypted	TRUE	Whether to encrypt network traffic

So, if c001n01 is an active cluster node and is listening on port 1234 for connections, and someuser is a member of the haclient group, then the following would prompt for someuser’s password and return the cluster’s current configuration:

# export CIB_port=1234; export CIB_server=c001n01; export CIB_user=someuser;
# cibadmin -Q

For security reasons, the cluster does not listen for remote connections by default. If you wish to allow remote access, you need to set the remote-tls-port (encrypted) or remote-clear-port (unencrypted) CIB properties (i.e., those kept in the cib tag, like num_updates and epoch).

Extra top-level CIB properties for remote access

CIB Property	Default	Description
remote-tls-port		Listen for encrypted remote connections on this port.
remote-clear-port		Listen for plaintext remote connections on this port.

Important

The Pacemaker version on the administration host must be the same or greater than the version(s) on the cluster nodes. Otherwise, it may not have the schema files necessary to validate the CIB.

Footnotes

[1]	For a list, see “Configuration Tools” at https://clusterlabs.org/components.html