Instance maintenance policies

You can configure an instance maintenance policy for your Auto Scaling group to meet specific capacity requirements during events that cause instances to be replaced, such as an instance refresh or the health check process.

For example, suppose you have an Auto Scaling group that has a small number of instances. You want to avoid the potential disruptions from terminating and then replacing an instance when health checks indicate an impaired instance. With an instance maintenance policy, you can make sure that Amazon EC2 Auto Scaling first launches a new instance and then waits for it to be fully ready before terminating the unhealthy instance.

An instance maintenance policy also helps you minimize any potential disruptions in cases where multiple instances are replaced at the same time. You set the minimum and maximum healthy percentage parameters for the policy, and your Auto Scaling group can only increase and decrease capacity within that minimum-maximum range when replacing instances. A larger range increases the number of instances that can be replaced at the same time.