- `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))

*   The admission webhook configurations API, part of the admissionregistration API, is now at v1beta1. Delete any existing webhook configurations before you upgrade, and update your configuration files to use the latest API. For this and the previous...

- Fixed bug that caused a resource to include patch directives when using strategic merge patch against a non-existent field. ([#117568](https://github.com/kubernetes/kubernetes/pull/117568), [@alexzielenski](https://github.com/alexzielenski))

empty cgroupDriver value in the KubeletConfiguration is now always set to "systemd" unless the user is explicit about it. This requires existing machine setups to configure the container runtime to use the "systemd" driver. Documentation on this topic can be found here: https://kubernetes.io/docs/setup/production-environment/container-runtimes/. When upgrading existing clusters / nodes using "kubeadm upgrade" the old cgroupDriver value is preserved, but in 1.22 this change will also apply to "upgrade"....

* Fix a bug that preempting a pod may block forever. ([#65987](https://github.com/kubernetes/kubernetes/pull/65987), [@Random-Liu](https://github.com/Random-Liu))
* fix data loss issue if using existing azure disk with partitions in disk mount  ([#63270](https://github.com/kubernetes/kubernetes/pull/63270), [@andyzhangx](https://github.com/andyzhangx))

- Added new option to the `InterPodAffinity` scheduler plugin to ignore existing
  pods` preferred inter-pod affinities if the incoming pod has no preferred inter-pod
  affinities. This option can be used as an optimization for higher scheduling throughput
  (at the cost of an occasional pod being scheduled non-optimally/violating existing
  pods preferred inter-pod affinities). To enable this scheduler option, set the

* Add --no-negcache flag to kube-dns to prevent caching of NXDOMAIN responses. ([#66036](https://github.com/kubernetes/kubernetes/pull/66036), [@prameshj](https://github.com/prameshj))
* fix data loss issue if using existing azure disk with partitions in disk mount  ([#63270](https://github.com/kubernetes/kubernetes/pull/63270), [@andyzhangx](https://github.com/andyzhangx))

...

### Beta APIs Off by Default

[New beta APIs will not be enabled in clusters by default](https://github.com/kubernetes/enhancements/issues/3136).
Existing beta APIs and new versions of existing beta APIs, will continue to be enabled by default.

### Signing Release Artifacts

## Changelog since v1.19.15

## Changes by Kind

### Bug or Regression

- Fix detach from non-existant nodes and support dangling volumes (#104912, @gnufied) [SIG Cloud Provider and Storage]
- Revert PR #102925 which introduced unexpected scheduling behavior based on balanced resource allocation (#105526, @harisund) [SIG Scheduling]