Using custom directives

While directives for hosts such as host_name, alias, and address may be adequate for many purposes, depending on our monitoring requirements, we may sometimes need Nagios Core to be able to refer to other data that's specific to individual hosts but can't be included in one of these directives.

For example, it's common in networking to have a management interface for a device. This is a network interface that links to a network used only by the administrators of the device for the purposes of monitoring and configuring it and is not accessible to users of the service. While we may want to run, for example, check_ping against the public-facing address of a given host, we may also need to verify that a service at a different address on a completely different network is running.

We might have a host configured in the following way referring to a webserver and including a PING check to make sure its public-facing interface with the 203.0.113.1 address is up and running...