Defining the Pacemaker cluster (HA group)

The HA group is a Pacemaker cluster. You define the Pacemaker cluster by editing the /var/mqm/rdqm.ini file and running the rdqmadm command.

About this task

See https://clusterlabs.org/pacemaker/ for information about Pacemaker. You can create the Pacemaker cluster as a user in the mqm group if the mqm user can use sudo. If the user can also SSH to each server without a password, then you only need edit the rdqm.ini file and run rdqmadm on one of the servers to create the Pacemaker cluster. Otherwise you must create the file and run the command as root on each of the servers that are to be nodes.

The rdqm.ini file gives the IP addresses for all of the nodes in the Pacemaker cluster. You can define HA_Primary and HA_Secondary interfaces that are used for Pacemaker to monitor the system, but Pacemaker can instead use the replication interface, named HA_Replication, for this purpose, if required. The HA_Replication interface must have sufficient bandwidth to support replication requirements given the expected workload of all the RDQMs running in the HA Group.

[MQ 9.2.0 Jul 2020] For RHEL 8 installations you must give the name of each node, which must be the hostname as returned by the uname -n command. For RHEL 7 installations the specification of the node name is optional.

The following example file shows the configuration for an example Pacemaker cluster that uses a separate IP address for each interface:


Node:
  Name=rdqm-node-1.spiranthes.com
  HA_Primary=192.168.4.1
  HA_Alternate=192.168.5.1
  HA_Replication=192.168.6.1
Node:
  Name=rdqm-node-2.spiranthes.com
  HA_Primary=192.168.4.2
  HA_Alternate=192.168.5.2
  HA_Replication=192.168.6.2
Node:
  Name=rdqm-node-3.spiranthes.com
  HA_Primary=192.168.4.3
  HA_Alternate=192.168.5.3
  HA_Replication=192.168.6.3

The following diagram illustrates this configuration:

illustrates the configuration with a separate ip address for each interface

The following example file shows the configuration for an example Pacemaker cluster that uses the HA_Replication interface for monitoring. In this case you only specify the HA_Replication interface:


Node:
  Name=rdqm-node-1.spiranthes.com
  HA_Replication=192.168.4.1
Node:
  Name=rdqm-node-2.spiranthes.com
  HA_Replication=192.168.4.2
Node:
  Name=rdqm-node-3.spiranthes.com
  HA_Replication=192.168.4.3

The following diagram illustrates this configuration:

Shows the configuration using a single interface

If you wanted to use two IP addresses, your rdqm.ini file has an HA_Primary and an HA_Replication field for each node, but no HA_Alternate field:

Node:
  Name=rdqm-node-1.spiranthes.com
  HA_Primary=192.168.4.1
  HA_Replication=192.168.5.1
Node:
  Name=rdqm-node-2.spiranthes.com
  HA_Primary=192.168.4.2
  HA_Replication=192.168.5.2
Node:
  Name=rdqm-node-3.spiranthes.com
  HA_Primary=192.168.4.3
  HA_Replication=192.168.5.3

The following diagram illustrates this configuration:

shows the configuration using two interfaces

The order in which you specify the nodes must be the same in all the rdqm.ini files in your configuration. Your three nodes must have a common view as to which one is Node1, which one Node2 and so on.

Procedure

To define the Pacemaker cluster as user root:
1. Edit the /var/mqm/rdqm.ini file on one of the three servers so that the file defines the cluster.
2. Copy the file to the other two servers that will be nodes in the Pacemaker cluster.
3. Run the following command as root on each of the three servers:
```
rdqmadm -c
```
To define the Pacemaker cluster as a user in the mqm group on each node:
1. Ensure that the user mqm can use sudo to run commands.
2. Edit the /var/mqm/rdqm.ini file on one of the three servers so that the file defines the Pacemaker cluster.
3. Copy the /var/mqm/rdqm.ini to the other two servers that will be nodes in the Pacemaker cluster.
4. Run the following command on each server:
```
rdqmadm -c
```
To define the Pacemaker cluster as a user in the mqm group from one node:
1. Ensure that the user mqm can use sudo to run commands and can optionally connect to each server using SSH without a password.
2. Edit the /var/mqm/rdqm.ini file on one of the three servers so that the file defines the Pacemaker cluster.
3. Run the following command:
```
rdqmadm -c
```