* "volume.alpha.kubernetes.io/storage-class" does not have any special meaning. A default storage class
    * and  DefaultStorageClass admission plugin can be used to preserve similar behavior of Kubernetes cluster,
    * see https://kubernetes.io/docs/user-guide/persistent-volumes/#class-1 for details.

- Autoscaling/v2beta2 and custom_metrics/v1beta2 have been introduced, which implement metric selectors for Object and Pods metrics, as well as allowing AverageValue targets on Objects, similar to External metrics. ([#64097](https://github.com/kubernetes/kubernetes/pull/64097), [@damemi](https://github.com/damemi)) Courtesy of SIG API Machinery, SIG Architecture, SIG Autoscaling, SIG CLI, and SIG Testing

- ACTION REQUIRED: Support for basic authentication via the --basic-auth-file flag has been removed.  Users should migrate to --token-auth-file for similar functionality. ([#89069](https://github.com/kubernetes/kubernetes/pull/89069), [@enj](https://github.com/enj)) [SIG API Machinery]

- `kubectl debug` gains support for changing container images when copying a pod for debugging, similar to how `kubectl set image` works. See `kubectl help debug` for more information. ([#96058](https://github.com/kubernetes/kubernetes/pull/96058), [@verb](https://github.com/verb)) [SIG CLI]

### Documentation

Kubeadm: Expose the `kubeadm join` workflow as phases

- Kubeadm: added support for dry running `kubeadm reset`. The new flag `kubeadm reset --dry-run` is similar to the existing flag for `kubeadm init/join/upgrade` and allows you to see what changes would be applied. ([#107512](https://github.com/kubernetes/kubernetes/pull/107512), [@SataQiu](https://github.com/SataQiu))

- Kubeadm: when adding new control plane nodes with "kubeadm join", ensure that the etcd member addition is performed only if a given member URL does not already exist in the list of members. Similarly, on "kubeadm reset" only remove an etcd member if its ID exists. ([#127621](https://github.com/kubernetes/kubernetes/pull/127621), [@SataQiu](https://github.com/SataQiu)) [SIG Cluster Lifecycle]

    * - kubeadm upgrade apply supports all standard ways of specifying version via labels. Examples: stable-1.8, latest-1.8, ci/latest-1.9 and similar.
* - kubeadm 1.9 will detect and fail init or join pre-flight checks if kubelet is lower than 1.8.0-alpha ([#52913](https://github.com/kubernetes/kubernetes/pull/52913), [@kad](https://github.com/kad))

- Kubeadm: when adding new control plane nodes with "kubeadm join", ensure that the etcd member addition is performed only if a given member URL does not already exist in the list of members. Similarly, on "kubeadm reset" only remove an etcd member if its ID exists. ([#127620](https://github.com/kubernetes/kubernetes/pull/127620), [@SataQiu](https://github.com/SataQiu)) [SIG Cluster Lifecycle]

### Other (Cleanup or Flake)

- Fixes a bug of identifying the correct containerd process. ([#97888](https://github.com/kubernetes/kubernetes/pull/97888), [@pacoxu](https://github.com/pacoxu))
- Fixes add-on manager leader election to use leases instead of endpoints, similar to what kube-controller-manager does in 1.20 ([#98968](https://github.com/kubernetes/kubernetes/pull/98968), [@liggitt](https://github.com/liggitt))