Amazon EC2 Auto Scaling customers in the AWS GovCloud (US) Regions can now hibernate their Warm Pool instances. With Warm Pools, customers can scale out faster by bringing instances into service from a pre-initialized pool of EC2 instances. Warm Pools are a good fit for applications that have time consuming initialization steps — like loading gigabytes of data, provisioning services, or running custom scripts — that can take several minutes or longer before those EC2 instances are ready to serve traffic.
Source:: Amazon AWS