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 host/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 if an application is locked and requires a restart upon detection.