Monitoring individual nodes in a cluster

In this recipe, we'll learn how to monitor a collection of hosts in a cluster, using the check_cluster plugin included in the standard Nagios Plugins. Being able to monitor more than one host collectively is useful in situations with redundancy; one of a set of hosts being DOWN, perhaps for power conservation or maintenance reasons, is not necessarily a cause for notification. However, if a larger number or all of the hosts were down, we would definitely want to be notified. Using check_cluster allows us to arrange this.

Getting ready

You will need a Nagios Core 3.0 or newer server, and have shell access to change its backend configuration. You will also need to have at least two monitored hosts in a redundant setup for some function, such as database replication, DNS servers, or load-balanced web servers.

You should also be familiar with the way hosts and services are defined, and in particular defining commands; these concepts are discussed in Chapter...