Random Pod Selection on ReplicaSet Downscale

The current downscaling algorithm for ReplicaSets prefers to delete Pods that have been running for the least amount of time. This heuristic attempts to minimize disruption under the premise that newer Pods are likely to be serving a lesser amount of clients. However, the heuristic can be detrimental to high availability requirements: when a ReplicaSet lands in an imbalanced state across failure domains, the heuristic tends to preserve the imbalance after repeated up and down scales. We propose a randomized approach to the downscale Pod victim selection algorithm of the ReplicaSet controller to mitigate ReplicaSet imbalance across failure domains.