Acting on alarm changes
CloudWatch can notify users on two types of alarm changes: when an alarm changes state, and when the configuration of an alarm gets updated.
When an alarm evaluates, it might change from one state to another, such as ALARM, OK or INSUFFICIENT_DATA. These alarm state changes can signal a possible incident, a return to normal, or a metric being unavailable. In such cases, you might want to engage or notify users using either of the following options:
You can configure the alarm to send a notification to a SNS topic as part of the alarm’s actions. An SNS topic can then be configured for application-to-application (A2A) messaging as well as application-to-person (A2P) notifications, including channels such as email notifications and SMS. All the destinations that you define for your SNS topic receive the alarm notification. For more information, see Amazon SNS event destinations.
You can configure notifications for alarm state change events. Amazon User Notifications offers a native way to configure such notifications and is the recommended approach.
Additionally, CloudWatch sends events to Amazon EventBridge whenever alarms change state, and when alarms are created, deleted, or updated. You can write EventBridge rules to take actions or be notified when EventBridge receives these events.