Establishing a service dependency

In this recipe, you'll learn how to establish a service dependency between two services. This feature can be used to control how Nagios Core checks for hosts and notifies about problems in situations where if one host is in a PROBLEM state, it implies that at least one other service is necessarily also in the PROBLEM state.

Getting ready

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 services defined, one of which is by definition dependent on the other; this means that if the depended-upon service were to enter CRITICAL state, then it would imply that the dependent service would also be CRITICAL.

We'll use a simple example: let's suppose that we are testing authentication to a mailserver marathon.example.net with a service MAIL_LOGIN and also checking a database service MAIL_DB on the same host that stores the login usernames and password hashes.

In this situation...