The Amazon EC2 Auto Scaling Instance Refresh feature enables customers to update the EC2 instances in their Auto Scaling groups on a rolling basis. Now, Instance Refresh gives customers more control over the update process by letting them configure Instance Refresh checkpoints to phase their deployments. An Instance Refresh checkpoint specifies what percent of the Auto Scaling group’s instances should be replaced and how long to wait before continuing with the rolling update. This gives customers time to perform any necessary validation or testing steps at various checkpoints.
Source:: Amazon AWS