Nagios has many places where it can be extended with external scripts or applications. We have also learned that Nagios is not bound to any specific language and that its real power comes from the fact that you can choose the language you'll use to program your code.

In this chapter, we learned how to create our own plugins to perform active checks. Adding our own commands makes it possible to perform checks using techniques that might not be available using the default Nagios plugin commands. We have also learned how it can be used to create various types of plugins—checking database consistency, monitoring system time differences, websites, and cloud environments.

This chapter also covered how to use passive checks and supply the check results to Nagios. In such a case, we are responsible for performing the test and sending results to Nagios. Nagios will then handle all of the results of the new status for a host or service, such as triggering event handlers and sending notifications...