Alarms offer monitoring-as-a-service for all the resources running on OpenStack. This efficiency monitoring service helps us to scale automatically in and out of a group of instances using orchestration services. Alarm is useful for notifying you about the health of the cloud’s resources, which means how they are being used, in what amount, are the resources enough, and others.  Alarms follow a tri-state model-  ok- means the rule that governs the alarm is evaluated as “false”.  alarm- means the alarm's rule is evaluated as “true”.  insufficient data- means there are not enough data points in the evaluation periods for determining the alarm state.