Administrative Procedures for RHEL High Availability Clusters - Enabling Cluster Daemons to Start on Boot

Updated

Contents

Overview

Applicable Environments

  • Red Hat Enterprise Linux (RHEL) 7, 8 with the High Availability Add-On

Situations Where This Procedure May Be Useful

  • Cluster nodes are running successfully, and administrators would like nodes to rejoin the cluster automatically on reboot
  • Some nodes are enabled to start on boot, and the rest need to be.
  • A new node has been added and needs to be set to start on boot.
  • Cluster services were disabled on boot for maintenance or troubleshooting, and now are ready to be enabled again.

What This Procedure Accomplishes

The nodes that are currently available and being operated on in this procedure will have their pacemaker service enabled in systemd, causing it to start automatically on any subsequent boots. This will lead to the nodes attempting to communicate with each other, form a membership amongst any that are present, and begin participating in the cluster.

If other members of the cluster are not present or able to communicate at the time this procedure is run, those nodes will not have cluster daemons enabled.

NOTE: The pacemaker.service systemd unit automatically starts corosync.service as a dependency. It does not need to be enabled.

Procedure: Enabling Cluster Daemons to Start on Boot

Consideration: Should Cluster Daemons Be Enabled?

Having nodes rejoin a cluster automatically can avoid prolonged periods of a cluster operating with a degraded membership, which is often ideal. But there are some scenarios where preventing an automatic rejoin could be beneficial. The tradeoffs associated with enabling services vs keeping them disabled should be considered.

Optional Task: Start and Authenticate pcsd

If pcs will be used to manage the state of the nodes as far as being started or stopped, enabled or disabled (on boot), then pcsd will need to be running.

If the node(s) where pcs commands will be executed from has not yet authenticated to each node's pcsd daemon - such as if this cluster was just created or any node was recently added - then authentication will need to be performed first.

Task: Enable Cluster Services

If the nodes of the cluster should automatically join the cluster on any subsequent boots, then enable the High Availability services throughout the cluster. This can be done with pcs if pcsd is running:

# pcs cluster enable --all

Or from individual nodes, if preferred:

# pcs cluster enable

Or from one node, enabling individual nodes by name:

# # Syntax: # pcs cluster enable [nodename]
# # Example:
# pcs cluster enable node1.example.com

If pcsd is not running, then systemctl can enable the pacemaker service to start on boot from each node:

# systemctl enable pacemaker.service
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