* `federation/deploy/deploy.sh` was an interim solution introduced in Kubernetes v1.4 to simplify the federation control plane deployment experience. Now that we have `kubefed`, we are deprecating `deploy.sh` scripts. ([#38902](https://github.com/kubernetes/kubernetes/pull/38902), [@madhusudancs](https://github.com/madhusudancs))

* [alpha] Improve Flex volume deployment

  * Flex volume driver deployment is simplified in the following ways:

    * New driver files can now be automatically discovered and initialized without requiring a kubelet or controller-manager restart.

    * A sample DaemonSet to deploy Flexvolume drivers is now available.

* [prototype] Volume snapshots

* The Deployment, DaemonSet, and ReplicaSet kinds in the extensions/v1beta1 group version are now deprecated, as are the Deployment, StatefulSet, and ControllerRevision kinds in apps/v1beta1. As they will not be removed until after a GA version becomes available, you may continue to use these kinds in existing code. However,...

  - [**Notable Features**](#notable-features)
  - [Kubefed](#kubefed)
    - [**Kubernetes API**](#kubernetes-api)
      - [User Provided Extensions](#user-provided-extensions)
    - [**Application Deployment**](#application-deployment)
      - [StatefulSet](#statefulset)
      - [DaemonSet](#daemonset-1)
      - [Deployments](#deployments)
      - [PodDisruptionBudget](#poddisruptionbudget)
    - [**Security**](#security)

* `kubectl rollout undo` now returns errors when attempting to rollback a deployment to a non-existent revision ([#70039](https://github.com/kubernetes/kubernetes/pull/70039), [@liggitt](https://github.com/liggitt))
    * `kubectl rollout undo` no longer uses the deprecated extensions/v1beta1 rollback API, which means that Events are no longer emitted when rolling back a deployment

- ReplicaSets and Deployments should always count `.status.availableReplicas` at the correct time without a delay. This results in faster reconciliation of Deployment conditions and faster, unblocked Deployment rollouts. ([#132121](https://github.com/kubernetes/kubernetes/pull/132121), [@atiratree](https://github.com/atiratree)) [SIG Apps]

* new dhcp-domain parameter to be used for figuring out the hostname of a node ([#61890](https://github.com/kubernetes/kubernetes/pull/61890), [@dims](https://github.com/dims))
* Extend the Stackdriver Metadata Agent by adding a new Deployment for ingesting unscheduled pods, and services.   ([#62043](https://github.com/kubernetes/kubernetes/pull/62043), [@supriyagarg](https://github.com/supriyagarg))

    * Default value for expendable pod priority cutoff in GCP deployment of Cluster Autoscaler changed from 0 to -10.
    * action required: users deploying workloads with priority lower than 0 may want to use priority lower than -10 to avoid triggering scale-up.

### Other notable changes

## Changelog since v1.20.0

## What's New (Major Themes)

### Deprecation of PodSecurityPolicy

- Kube-controller-manager: Fixes bug setting headless service labels on endpoints ([#85361](https://github.com/kubernetes/kubernetes/pull/85361),...