In this recipe, you'll learn how to monitor a collection of hosts in a cluster using the
check_cluster plugin included in the Nagios Plugins standard. Being able to monitor more than one host collectively is useful in situations with redundancy; one of a set of hosts being in the
DOWN state, 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.
You will need Nagios Core 4.0 or a newer server and to 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, nameservers, or load-balanced web servers.
You should also be familiar with the way hosts and services are defined, writing commands in particular; these concepts are discussed...