Nagios is one of the most widely adopted open source IT infrastructure monitoring tools, whose main interesting feature is the fact that it does not know how to monitor anything. Well, it sounds like a joke, but actually Nagios can be defined as an evaluating core, which takes some information as input and reacts accordingly. How is this information gathered? It is not the main concern of this tool and this leads us to an interesting point: Nagios leaves the task of getting the monitored data to an external plugin, which knows the following details:
- How to connect to the monitored services
- How to collect the data from the monitored services
- How to evaluate the data
Inform Nagios if the values gathered are beyond or in the boundaries to raise an alarm.
So, a plugin does a lot of things and one would ask oneself what does Nagios do then? Imagine it as an exchange...