- When scaling down a ReplicaSet, delete doubled up replicas first, where a "doubled up replica" is defined as one that is on the same node as an active replica belonging to a related ReplicaSet.  ReplicaSets are considered "related" if they have a common controller (typically a Deployment). ([#80004](https://github.com/kubernetes/kubernetes/pull/80004), [...

    * replicas, readyReplicas, currentReplicas, and updatedReplicas. The semantics of replicas is now consistent with DaemonSet and ReplicaSet, and readyReplicas has the semantics that replicas did prior to this release.

- Output for the `ScalingReplicaSet` event has changed from:
      Scaled <up|down> replica set <replica-set-name> to <new-value> from <old-value>
  to:
      Scaled <up|down> replica set <replica-set-name> from <old-value> to <new-value>. ([#125118](https://github.com/kubernetes/kubernetes/pull/125118), [@jsoref](https://github.com/jsoref)) [SIG Apps and CLI]

#### Application Deployment
* StatefulSetStatus now tracks replicas, readyReplicas, currentReplicas, and updatedReplicas. The semantics of replicas is now consistent with DaemonSet and ReplicaSet, and readyReplicas has the semantics that replicas did prior to 1.7 ([#46669](https://github.com/kubernetes/kubernetes/pull/46669), [@kow3ns](https://github.com/kow3ns)).

    - [DaemonSet](#daemonset-1)
    - [Deployment](#deployment-2)
    - [Node](#node)
    - [Pod](#pod)
    - [Pod Security Policy](#pod-security-policy)
    - [RBAC](#rbac-2)
    - [ReplicaSet](#replicaset)
    - [Secrets](#secrets)
    - [Service](#service-1)
    - [StatefulSet](#statefulset-1)
    - [Taints and Tolerations](#taints-and-tolerations)
    - [Volumes](#volumes-2)

  - A `create` or `update` API request with duplicate items in a keyed list no longer wipes out managedFields. Examples include env var entries with the same name, or port entries with the same containerPort in a pod spec.

Extensibility. SIG API Machinery added a new class of admission control webhooks (mutating), and brought the admission control webhooks to beta.

### Apps

The core workloads API, which is composed of the DaemonSet, Deployment, ReplicaSet, and StatefulSet kinds, has been promoted to GA stability in the apps/v1 group version. As such, the apps/v1beta2 group version is deprecated, and all new code should use the kinds in the apps/v1 group version.

### Auth

- Fixed a bug that caused duplicate validation when updating a ReplicaSet. ([#131873](https://github.com/kubernetes/kubernetes/pull/131873), [@gavinkflam](https://github.com/gavinkflam)) [SIG Apps]

## Changes by Kind

### API Change

- Make STS available replicas optional again, ([#109241](https://github.com/kubernetes/kubernetes/pull/109241), [@ravisantoshgudimetla](https://github.com/ravisantoshgudimetla)) [SIG API Machinery and Apps]
- Make STS available replicas optional again. ([#113122](https://github.com/kubernetes/kubernetes/pull/113122), [@ashrayjain](https://github.com/ashrayjain)) [SIG Apps]

- The `controller.kubernetes.io/pod-deletion-cost` annotation can be set to offer a hint on the cost of deleting a `Pod` compared to other pods belonging to the same ReplicaSet. Pods with lower deletion cost are deleted first. This is an alpha feature. ([#99163](https://github.com/kubernetes/kubernetes/pull/99163), [@ahg-g](https://github.com/ahg-g))