https://aws.amazon.com/about-aws/whats-new/2021/04/amazon-ec2-auto-scaling-introduces-warm-pools-accelerate-scale-out-while-saving-money/

https://aws.amazon.com/blogs/compute/scaling-your-applications-faster-with-ec2-auto-scaling-warm-pools/

If we could keep X instances warmed up, we could start jobs much faster without having to set the min count on the asg to something non-zero.

It should be added soon to cloudformation: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-as-group.html