1. Setting Up High Availability Clustering
  2. Configuring Pacemaker Resources and Resource Groups

4 Configuring Pacemaker Resources and Resource Groups

Pacemaker enables you to create groups of resources, such as database and file system services, so that they start in the order you specify and stop in the reverse of that order. Adding resources to the same resource group also ensures that they run on the same node.

About Pacemaker Resources and Resource Groups

A Pacemaker resource, at its most basic, is a service managed by Pacemaker. Example of resources include services for the following:

  • IP address

  • File system

  • Website

  • Database

The resources in the preceding list are known as primitive resources. Primitive resources can be grouped and cloned into more complex resources called groups and clones.

Resource Agents

Each primitive resource is managed by a resource agent script that provides Pacemaker with access to the resource through a standardized interface. Some of the standards compatible with Pacemaker are shown in the following list:

  • Open Cluster Framework (OCF)

  • Systemd

  • System Services

  • STONITH

  • Linux Standard Base (LSB)

WARNING:

LSB scripts do not always comply with the standard. See https://clusterlabs.org/ for more information.

To see the resource agents on your system, you can run the pcs resource agents command as shown in the following example (lots of lines have been omitted from the sample output for brevity): 

pcs resource agents
.
.
.
apache
.
.
.
IPaddr
IPaddr2
.
.
.
oracle
oralsnr
pacemaker
pacemaker
.
.
.
pcsd
pcsd
.
.
.

To see the interface standards on your system you can run the pcs resource standards command as shown in the following example: 

pcs resource standards
lsb
ocf
service
systemd

Resource Properties

Resource properties determine which resource agent manages the resource, where to find that resource agent and which standards it conforms to. The following list describes the properties of a primitive resource:

id

This is the resource name of your choice.

class

The standard the resource agent conforms to.

For example: ocf, stonith, or systemd.

description

Description of the resource agent.

type

The type of the resource agent you need to use.

For example, IPaddr2, Filesystem, or Website.

provider

With OCF agents you can specify the provider to use for a resource (the OCF spec allows multiple vendors to supply the same resource agent).

Example values: heartbeat, pacemaker.

Creating Resources

You can create a resource by using the pcs resource create command as shown in the following example that creates a resource for a virtual IP address: 

sudo pcs resource create MyVirtualIP ocf:heartbeat:IPaddr2 ip=192.0.2.3 \
cidr_netmask=24 nic=eth1 \
op monitor interval=1s --group myapachegroup

In the preceding example:

  • MyVirtualIP is the id, or name of the resource.

  • ocf is the class, or the standard, the resource agent conforms to.

  • heartbeat is the provider of the resource.

  • IPaddr2 is the type of resource that is to be created.

    The following options are specified for the IPaddr2 resource:

    • ip=192.0.2.3 specifies IP address to use for the Virtual IP Address.

    • cidr_netmask=24 specifies the netmask for the interface in CIDR format.

    • nic=eth1 The base network interface on which the IP address will be brought online.

    The following operation is specified for the IPaddr2 resource:

    • op monitor interval=1s specifies that the system checks every second whether the resource is running.

  • --groupmyapachegroup specifies the resource group to which the resource is to be added. If the group does not exist, it is created.

Following on from the preceding example, you can create and add a second resource, this time of type apache, as shown in the following example: 

sudo pcs resource create MyApacheWebsite ocf:heartbeat:apache \
configfile="/etc/httpd/conf/httpd.conf" \
statusurl="http://192.0.2.3/server-status" --group myapachegroup

You can confirm the status of your resources by running the pcs status command. Depending upon your configuration, you r command output will be similar to the following sample code block: 

sudo pcs status
Cluster name: my_cluster
Cluster Summary:
* Stack: corosync (Pacemaker is running)
* Current DC: node1 (version 2.1.6-9.1.0.1.el8_9-
6fdc9deea29) - partition with quorum
* Last updated: Sat Feb 3 22:35:58 2024 on node1
* Last change: Sat Feb 3 22:33:37 2024 by root via
cibadmin on node1
* 2 nodes configured
* 4 resource instances configured
Node List:
* Online: [ node1 ]
* OFFLINE: [ node2 ]
Full List of Resources:
* Resource Group: myapachegroup:
 * MyVirtualIP (ocf::heartbeat:IPaddr2): Started node1
 * MyApacheWebsite (ocf::heartbeat:apache): Started node1
...
...
Daemon Status:
corosync: active/disabled
pacemaker: active/enabled
pcsd: active/enabled

Resource Start and Stop Order in a Resource Group

If the resource group in the preceding examples, myapachegroup, is started from a stopped status, the resources will be started in the order they were added to the group:

  1. MyVirtualIP , the first resource to be added to the resource group, will be started first.

  2. MyApacheWebsite, the second resource to be added to the resource group, will be started second.

Conversely, when the resource group is stopped, the resources will be stopped in the opposite order of that in which they were added to the group:

  1. MyApacheWebsite, the last resource added to the resource group in the preceding examples, will be stopped first.

  2. MyVirtualIP , the first resource added to the resource group in the preceding examples, will be stopped last.

You can also explicitly set the start order by using options --before or --after when creating a resource with the pcs resource create command to specify the position of the resource being created relative to a resource that already exists in the group.

The pcs resource group add command also enables you to specify resource sequence. See Creating a Resource Group for more information.

Creating a Resource Group

As documented in the preceding sections, using the pcs resource create command will create the group specified with the --group option if it does not already exist. A second way of creating a resource group is by using the pcs resource group add command, as shown in the following example: 

sudo pcs resource group add mygroup MyVirtualIP MyApacheWebsite

The preceding command creates group mygroup If it does not already exist, and adds existing resources MyVirtualIP and MyApacheWebsite to the group. If the resources specified in the command are in another group, they will be moved to the new group mygroup.

You can also use options --before or --after with the pcs resource group add command to specify the position of the resource being created relative to a resource that already exists in the group.

See pcs(8) and https://clusterlabs.org/ for more information on configuring resources and resource groups.