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.


See https://clusterlabs.org/pacemaker/ for information about Pacemaker. We 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 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. We can specify that the Pacemaker cluster uses one, two, or three IP addresses. The interface that is used for synchronous data replication is named the 'replication interface'. The interface must have sufficient bandwidth to support replication requirements given the expected workload of all the RDQMs running in the HA Group. The primary and secondary interfaces are used for Pacemaker to monitor the system, but Pacemaker can use the replication interface for this purpose, if required.

For RHEL 8 installations we 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 are 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 example file shows the configuration for an example Pacemaker cluster that uses the same IP address for each interface. In this case you only specify the 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
If we wanted to use two IP addresses, your rdqm.ini file has a Primary and a Replication field for each node, but no 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 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

Parent topic: RDQM high availability


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