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Cloud Computing · Intermediate

CloudWatch Alarm

CloudWatch feature that watches a metric or expression and changes state (OK, ALARM, INSUFFICIENT_DATA) to trigger actions.

Definition

Alarms evaluate a metric against a threshold over a number of periods and can invoke SNS notifications, Auto Scaling policies, EC2 actions (stop, terminate, reboot, recover) or Systems Manager actions. Composite alarms combine multiple alarms to reduce noise.

Example

An alarm on StatusCheckFailed_System automatically recovers the instance onto new hardware.

Exam tip

Know the three alarm states, and that EC2 auto recovery is driven by a system status check alarm.

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