Icinga is an enterprise grade open source monitoring system which keeps watch over networks and any conceivable network resource, notifies the user of errors and recoveries and generates performance data for reporting. Scalable and extensible, Icinga can monitor complex, large environments across dispersed locations.
Icinga is a fork of Nagios® and is backward compatible. So, Nagios® configurations, plugins and addons can all be used with Icinga. Though Icinga retains all the existing features of its predecessor, it builds on them to add many long awaited patches and features requested by the user community.
Icinga 2 is a network monitoring system and parallel development branch to Icinga 1.x. It is a core framework replacement (no GUI) that seeks build on the success of Icinga 1.x and deal with shortcomings inherited from Nagios as a fork.