Validate Kubernetes HPA scale-to-zero metric choices before deployment
A HorizontalPodAutoscaler can reduce the replica count of a Deployment, but minReplicas: 0 changes the question from how to scale down to how a workload starts again. A CPU or memory metric describes Pods that already exist. When the target has zero Pods, there is no Pod CPU or memory value for the controller to use as a wake-up signal.
Kubernetes v1.37 moves HPA scale-to-zero support to beta and enables it by default. The supported use is an HPA using an external or object metric, such as queue depth, a pending-work count, or another signal that remains available while the workload has no Pods. The release notes explicitly exclude CPU and memory metrics from scale-to-zero because they depend on active Pods.