In this case the alarm watches a metric every 5 minutes for 10 intervals. Thus, it needs at least 50 minutes to come to the "OK" state.Till then it will be in the INSUFFUCIENT_DATA state. Since 90 minutes have passed and CPU utilization is at 80% constant, the state of alarm will be "ALARM". Reference: http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/AlarmThatSendsEmail.ht ml