Starting today, you can use Amazon CloudWatch alarms to trigger an instance refresh rollback. EC2 Auto Scaling’s instance refresh allows you to perform a rolling replacement of instances in an Auto Scaling group, and instance refresh rollback can undo changes an instance refresh made if the instance refresh cannot complete as desired. With this launch, you can configure Auto Scaling to monitor CloudWatch alarms during an instance refresh, and automatically revert any changes made if the alarms are triggered.
Source:: Amazon AWS