How to check MongoDB replication lag in Icinga2 and get notified when it is over 15 seconds?

We assume here that you have a replica set in place. First download the python script for our nagios plugin:

cd /usr/lib/nagios/plugins
 git clone git://github.com/mzupan/nagios-plugin-mongodb.git

Now the Icinga2 part. You first need to create a command for replication lag check:

cd /etc/icinga2/conf.d/commands

Create a new file replication_lag.conf:

object CheckCommand "check_replication_lag" {
     import "plugin-check-command"
     command = [ PluginDir + "/nagios-plugin-mongodb/check_mongodb.py", "-A", "replication_lag" ]
     arguments = {
         "-H" = "$mongo_host$"
         "-P" = "$mongo_port$"
     }
 }

Create a new file in services folder called replication_lag.conf:

apply Service for (display_name => config in host.vars.replication) {
     import "generic-service"
     check_command = "check_replication_lag"
     vars += config
     assign where host.vars.replication
 }

This service gets enabled where it finds replication in host config. Now in secondary mongoDB hosts configuration add the below part:

vars.replication["Secondary DB"] = {
     mongo_host = "slave.example.com"
     mongo_port = 27017
 }

#sysadmin #icinga2 #mongodb #replication #replication_lag #nagios_plugin