Nagios is an infrastructure monitoring solution utilized to monitor just about any aspect of network infrastructure or application health. The heart of Nagios revolves around two primary concepts—scheduling checks and responding to events. Nagios takes in a user-defined configuration of hosts, services, and contacts, and schedules checks to be run at regular intervals to verify the health of various hosts and services. When the status of a host or service changes, Nagios triggers an event, and can take actions such as sending an e-mail or opening a ticket in an external ticketing application. What's so great about Nagios as a technology? In a simple word—flexibility—as shown in the following bullet list:
Nagios does all of its monitoring through the user-defined check plugins, which are various scripts and binaries developed to monitor a specific metric or status. This means that there is no limit to what can be monitored by Nagios. If anything plugs into or runs on a computer, it can be monitored by Nagios.
Thousands of check plugins have been developed by the Nagios community to monitor virtually any type of hardware or software.
Nagios continually schedules and initiates regular checks of monitored hosts and services. Any host or service check that Nagios schedules and executes is known as an active check.
Nagios responds to host or service state changes, or events, using user-definable event handlers, which can be anything from a simple mail command to a custom script that automatically fixes the problem that was detected.
Nagios can also act as a listener to simply receive and process check results from remote locations. These are known as passive checks.
Nagios can be extended with various add-ons to provide data visualization, historical trending, and large environment scalability.
