- Trigger notifications or automated actions when a metric breaches a threshold.
- Comparison options include sampling, percentage, max, min, etc.
Alarm States
- OK – Metric is within threshold.
- INSUFFICIENT_DATA – Not enough data to evaluate.
- ALARM – Metric is outside threshold.
Period
- Evaluation interval in seconds.
- High-resolution custom metrics: 10s, 30s, or multiples of 60s.
CloudWatch Alarm Targets
- Amazon EC2: stop, terminate, reboot, or recover instances.
- EC2 Auto Scaling: trigger scaling actions.
- Amazon SNS: send notifications that can trigger Lambda, emails, HTTP/S calls, etc.
Composite Alarms
- Monitor the state of multiple other alarms.
- Combine with AND / OR conditions.
- Reduces alarm noise by alerting only on relevant combinations.
- Can trigger SNS notifications.