This article will help you get started with Pacemaker's Notification/Alert Agents.
As an example to get you a little familiar with how the alert agents work, I've created the script below in '/usr/local/bin/notification-agent-example.sh':
#!/bin/bash
### list of variables passed from Pacemaker to all alert agents:
# CRM_notify_recipient the configure recipient
# CRM_notify_node name of affected node
# CRM_notify_desc details about event
# CRM_notify_task requested fencing/resource opertion (fencing and resource notify only)
# CRM_notify_rc return code from operation (fencing and resource notify only)
# CRM_notify_rsc name of the affected resource (resource notify only)
# CRM_notify_target_rc expected return code of an operation (resource notify only)
# CRM_notify_status numerical code used by Pacemaker to represent operation result (resource notify only)
### some variables won't get values; set NA if not populated:
CRM_notify_recipient="${CRM_notify_recipient:-NA}"
CRM_notify_node="${CRM_notify_node:-NA}"
CRM_notify_desc="${CRM_notify_desc:-NA}"
CRM_notify_task="${CRM_notify_task:-NA}"
CRM_notify_rc="${CRM_notify_rc:-NA}"
CRM_notify_rsc="${CRM_notify_rsc:-NA}"
CRM_notify_target_rc="${CRM_notify_target_rc:-NA}"
CRM_notify_status="${CRM_notify_status:-NA}"
### do something with these values
logger "PCMK-NOTIFY: recipient: $CRM_notify_recipient"
logger "PCMK-NOTIFY: affected node: $CRM_notify_node"
logger "PCMK-NOTIFY: event details: $CRM_notify_desc"
logger "PCMK-NOTIFY: requested op: $CRM_notify_task"
logger "PCMK-NOTIFY: op ret code: $CRM_notify_rc"
logger "PCMK-NOTIFY: affected res: $CRM_notify_rsc"
logger "PCMK-NOTIFY: expected rc: $CRM_notify_target_rc"
logger "PCMK-NOTIFY: pcmk result: $CRM_notify_status"
### exit
exit 0
NOTE: You can get some more information regarding external-agents and the variables that are populated here: https://clusterlabs.org/pacemaker/doc/en-US/Pacemaker/2.0/html-single/Pacemaker_Explained/#_alert_agents
Once your script is in place on both nodes, you can configure the following in your Pacemaker configuration:
primitive cluster-notifications ocf:pacemaker:ClusterMon \
params user=root update=30 \
extra_options="--watch-fencing -E /usr/local/bin/notification-agent-example.sh"
clone cl-cluster-notifications cluster-notifications
After that, your script will be called for each resource operation that happens in the cluster; this includes all resource starts/stops (so anytime a failover happens many alerts will be generated), when a resource monitor operation is first started, and anytime a monitor operation fails.
As long as the "--watch-fencing" flag is in your "cluster-notifications" Pacemaker resource, Pacemaker will generate an alert when fencing is started and when monitoring is started for that node, which would imply that a member just joined the cluster.
Reviewed 2020/12/03 - DGT