Check cluster health via nagios plugin

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We can monitor cluster health using nagios plugin using: Not tested in production

1. Create a plugin to be called via nrpe on the cluster host '/usr/lib64/nagios/plugins/cluster_check.sh' with:

   #!/bin/bash
   
   # Run crm status command and capture output
   crm_output=$(crm status 2>&1)
   
   # Check for error or warning in output, ignoring case
   if [[ "$crm_output" =~ error || "$crm_output" =~ warning ]]; then
     # Send email alert with hostname and IP
     hostname=$(hostname)
     ip=$(hostname -I | awk '{print $1}')
     echo "Cluster status is not healthy on $hostname ($ip)!" 
     exit 2 # Nagios exit code for critical
   fi
   
   # Check if all nodes are online
   if [[ "$crm_output" =~ Online:\ \[\ (.*)\ \] ]]; then
     online_nodes=${BASH_REMATCH[1]}
     if [[ "$online_nodes" =~ \[.*\] ]]; then
       # Send email alert with hostname and IP
       hostname=$(hostname)
       ip=$(hostname -I | awk '{print $1}')
       echo "Not all nodes are online on $hostname ($ip)!"
       exit 2 # Nagios exit code for critical
     fi
   fi
   
   # Check if all resources are started
   if [[ "$crm_output" =~ Full\ list\ of\ resources:\$'\n'\ (.*) ]]; then
     resources=${BASH_REMATCH[1]}
     if [[ "$resources" =~ \*\* ]]; then
       # Send email alert with hostname and IP
       hostname=$(hostname)
       ip=$(hostname -I | awk '{print $1}')
       echo "Not all resources are started on $hostname ($ip)!" 
       exit 2 # Nagios exit code for critical
     fi
   fi
   
   echo "Cluster status is healthy!"
   exit 0 # Nagios exit code for OK

2. Edit '/etc/nagios/nrpe.conf' to have below:

   command[check_cluster_status]=/usr/lib64/nagios/plugins/cluster_check.sh

3. Restart nrpe on the cluster machine
4. Then configure remote service check using above plugin for appropriate host using below nagios service configuration:

   define host {
       use           linux-server
       host_name     example-host
       alias         Example Host
       address       192.0.2.100
   }
   
   define service {
       use                 generic-service
       host_name           example-host
       service_description Check Cluster Status
       check_command       check_nrpe!check_cluster_status
       check_interval      60 ; Check every 60 seconds
       retry_interval      10 ; Retry every 10 seconds if check fails
       notification_interval 120 ; Send a notification every 2 hours
       contact_groups      admins
   }

5. Restart nagios service on server
6. Validate whether proper health of cluster status is being captured
7. Optionally stop a resource and see whether latest status is reflected properly. Consider adding a virtual IP for testing in production systems. This virtual IP can be removed after testing.

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