Icinga

Icinga 2 watches whether the machines and services on a network are actually up, tells the right people when they are not, and records performance data that reporting can be built on. It is aimed at environments too large or too scattered for a single check host to cover.

Icinga 2 is the monitoring server, and a working stack pairs it with Icinga Web 2 for the interface. Configuration is plain text written in the Icinga DSL, or managed through the Icinga Director or a configuration management tool. Distributed setups spread checks across multiple locations, so a data center and private, public or hybrid clouds are watched from one system.

The documentation covers the pieces an operator assembles around the server.

• Packages: builds for Debian, Ubuntu, Raspberry Pi OS, Fedora, RHEL, OpenSUSE, SLES, Amazon Linux, Windows and containers.
• Agent based monitoring: run checks on the monitored host itself rather than only from the server.
• REST API: query state and drive the running configuration programmatically.
• Template library: reuse the bundled check command definitions instead of writing each one.
• Modules: extend the stack with the many add-ons and integrations built around Icinga.

Licensing changed at version 2.16.0, where new releases moved to GPLv3 or later while every earlier version and existing source file stays GPLv2 or later, with an OpenSSL linking exception that matters only for OpenSSL 1.x. Community channels handle questions, Icinga partners sell professional support, and the upgrading chapter is worth reading before any major version jump.