Auto Scaling can start and stop the instance at a pre-defined time. Here, the total running time isunknown. Thus, the user has to use the CloudWatch alarm, which monitors the CPU utilization. The user can create an alarm that is triggered when the average CPU utilization percentage has beenlower than 10 percent for 24 hours, signaling that it is idle and no longer in use. When the utilizationis below the threshold limit, it will terminate the instance as a part of the instance action. Reference: http://docs.aws.amazon.com/AmazonCloudWatch/latest/DeveloperGuide/UingAlarmActions.htm