icinga2/doc/3.09-event-handlers.md

Event Handlers

Event handlers are defined as EventCommand objects in Icinga 2.

Unlike notifications event commands are called on every service state change if defined. Therefore the EventCommand object should define a command line evaluating the current service state and other service runtime attributes available through runtime macros. Runtime macros such as $SERVICESTATETYPE$ and $SERVICESTATE$ will be processed by Icinga 2 helping on fine-granular events being triggered.

Common use case scenarios are a failing HTTP check requiring an immediate restart via event command, or a an application is locked and requires a restart on detection.