Explanation: If you have attached a load balancer to your Auto Scaling group, you can have Auto Scaling include the results of Elastic Load Balancing health checks when it determines the health status of an instance. After you add ELB health checks, Auto Scaling will mark an instance as unhealthy if Elastic Load Balancing reports the instance state as Out of Service. Frequently, an Auto Scaling instance that has just come into service needs to warm up before it can pass the Auto Scaling health check. Auto Scaling waits until the health check grace period ends before checking the health status of the instance. While the EC2 status checks and ELB health checks can complete before the health check grace period expires, Auto Scaling does not act on them until the health check grace period expires. To provide ample warm-up time for your instances, ensure that the health check grace period covers the expected startup time for your application.
Reference:
http://docs.aws.amazon.com/autoscaling/latest/userguide/healthcheck…