A Deployment revision is a versioned record of a Deployment’s pod template and rollout state. Kubernetes represents each revision with an associated ReplicaSet, so older ReplicaSets preserve rollback history. section 15.2.6
The Deployment object does not contain the revision history directly. The Deployment controller retains associated ReplicaSets instead; `revisionHistoryLimit` controls how many remain, defaulting to 10. section 15.2.6
