What are the criteria used by the Auto Scaling Groups when reusing instances for Warm Pools ?

When you configure the Auto Scaling Group (ASG) warm pool instance reuse policy to reuse instances, the criteria used for selecting an instance typically depends on the specific implementation of the warm pool feature in the cloud provider's Auto Scaling service. However, in general, the details about the specific selection mechanism may not be explicitly provided in the documentation, as it's often managed by the underlying service.

In AWS Auto Scaling Groups, for example, the warm pool instance reuse policy is designed to help maintain a desired capacity in a more cost-effective way by reusing instances that were previously part of the warm pool instead of launching entirely new instances.

While AWS documentation doesn't explicitly state the exact criteria used for selecting a warm pool instance, here are some considerations:

Random Selection: The Auto Scaling service might randomly select an instance from the warm pool. This approach distributes the workload among previously warmed instances and can prevent potential issues with repeatedly reusing the same instance.

Last Instance Used: Alternatively, it might use a more straightforward approach by reusing the last instance that was drawn from the warm pool. This approach simplifies the logic and ensures a sequential usage of instances.