* kubeadm: Enable kubelet client certificate rotation ([#52196](https://github.com/kubernetes/kubernetes/pull/52196), [@luxas](https://github.com/luxas))
* Scheduler predicate developer should respect equivalence class cache ([#52146](https://github.com/kubernetes/kubernetes/pull/52146), [@resouer](https://github.com/resouer))

containers](https://kubernetes.io/docs/concepts/workloads/pods/ephemeral-containers/), it became more obvious how we can support developers with tooling built on top of `kubectl exec`. The addition of the `kubectl debug` [command](https://github.com/kubernetes/enhancements/blob/master/keps/sig-cli/1441-kubectl-debug/README.md) (it is alpha but your feedback is more than welcome), allows developers to easily debug their Pods inside the cluster. We think this addition is invaluable.  This command allows one to create...

## Changelog since v1.27.0

## Urgent Upgrade Notes 

### (No, really, you MUST read this before you upgrade)

- Action required for the custom scheduler plugin developers. 
  Here's the breaking change in `EnqueueExtension` in the scheduling framework. 

* kubeadm: Enable kubelet client certificate rotation ([#52196](https://github.com/kubernetes/kubernetes/pull/52196), [@luxas](https://github.com/luxas))
* Scheduler predicate developer should respect equivalence class cache ([#52146](https://github.com/kubernetes/kubernetes/pull/52146), [@resouer](https://github.com/resouer))

### API-machinery

PSP as an admission controller resource is being deprecated. Deployed PodSecurityPolicy's will keep working until version 1.25, their target removal from the codebase. A new feature, with a working title of "PSP replacement policy", is being developed in [KEP-2579](https://features.k8s.io/2579). To learn more, read [PodSecurityPolicy Deprecation: Past, Present, and Future](https://blog.k8s.io/2021/04/06/podsecuritypolicy-deprecation-past-present-and-future/).

With CSI the Kubernetes volume layer becomes truly extensible, allowing third party storage developers to write drivers making their storage systems available in Kubernetes without having to touch the core code.

CSI was first introduction as alpha in Kubernetes v1.9 and moved to beta in Kubernetes v1.10.

* Deprecate kubectl rolling-update  ([#61285](https://github.com/kubernetes/kubernetes/pull/61285), [@soltysh](https://github.com/soltysh))
* client-go developers: the new dynamic client is easier to use and the old is deprecated, you must switch. ([#62913](https://github.com/kubernetes/kubernetes/pull/62913), [@deads2k](https://github.com/deads2k))

  * Plugins

      * Introduces the ability to extend kubectl by adding third-party plugins. Developer preview, please refer to the documentation for instructions about how to use it. ([#37499](https://github.com/kubernetes/kubernetes/pull/37499), [@fabianofranz](https://github.com/fabianofranz))

- Service session affinity timeout tests are no longer required for Kubernetes network plugin conformance due to variations in existing implementations. New conformance tests will be developed to better express conformance in future releases. ([#112806](https://github.com/kubernetes/kubernetes/pull/112806), [@dcbw](https://github.com/dcbw)) [SIG Architecture, Network and Testing]