In this recipe, you'll learn how to implement a simple kind of redundancy for Nagios Core by running a second Nagios Core instance with a near-identical configuration on another machine.
This may seem like it would not need a recipe to implement. It should be reasonably straightforward to simply copy over the configuration for a Nagios Core system and run it concurrently. There are two main problems with this:
Every problem detected on the network will fire notification events twice. The administrator charged with looking after the pager might well find this unbearable!
Everything will be checked twice. On smaller networks with simple checks, this may not be too much of a concern, but it could be an issue on larger, busier networks.
This recipe will solve the first problem by configuring the slave monitoring server to suppress notifications until it detects an issue with the master server. In the There's More section, we'll discuss extending this solution...