Icinga2, the next generation, complete rewrite, of the Nagios fork Icinga, is an open source monitoring system which checks the availability of your network resources, notifies users of outages, and generates performance data for reporting.
Icinga 2 manages monitoring tasks, running checks, sending alert notifications. The Icinga 2 features can be enabled on-demand, be it default features such as the 'checker' or 'notification' component, or external interfaces compatible with Icinga 1.x and its user interfaces, for example the IDO DB (Icinga Data Out Database). Icinga 2 ships a built-in cluster stack secured by SSL x509 certificates attempting to make distributed monitoring setups more easy.
The configuration syntax is different to Icinga Core 1.x and Nagios and requires a migration on upgrade.