Alarms are used to trigger notifications for any metric. Options like sampling, percentage, max, min…
Alarm States: OK, INSUFFICIENT_DATA, ALARM
For example, you can set an alarm that triggers when CPU util is >95%. Then, you can trigger a reboot of the EC2 instance and an auto scaling action. You can also send a notification to your email.
CloudWatch Alarm Targets
- EC2 instances: Stop, terminate, reboot, recover
- Auto Scaling: Trigger auto scaling action of EC2
- SNS: Send notification to SNS (which then you can use for anything)
Composite Alarms
Normally, alarms are on single metric. If you want multiple metrics, you should use composite alarm, which monitors multiple metrics. You can use AND and OR conditions