* kubectl built for darwin from darwin now enables cgo to use the system-native C libraries for DNS resolution. Cross-compiled kubectl (e.g. from an official kubernetes release) still uses the go-native netgo DNS implementation.  ([#64219](https://github.com/kubernetes/kubernetes/pull/64219), [@ixdy](https://github.com/ixdy))

* Controller-manager --service-sync-period flag has been removed. (It was never used in the code and should have no user impact.) ([#59359](https://github.com/kubernetes/kubernetes/pull/59359), [@khenidak](https://github.com/khenidak))

* [beta] SelfSubjectRulesReview, an API that lets a user see what actions they can perform with a namespace, has been added to the authorization.k8s.io API group. This bulk query is intended to enable UIs to show/hide actions based on the end user, and for users to quickly reason about their own permissions.

* `kubectl create rolebinding` and `kubectl create clusterrolebinding` invocations must be updated to  specify multiple subjects as repeated  `--user`, `--group`, or `--serviceaccount` arguments instead of comma-separated arguments to a single `--user`, `--group`, or `--serviceaccount`.  E.g. `--user=x,y` must become `--user x --user y`  ([#43903](https://github.com/kubernetes/kubernetes/pull/43903), [@xilabao](https://github.com/xilabao))


### kubeadm

- kube-apiserver:

[alpha] Added an `--endpoint-reconciler-type` command-line argument to select the endpoint reconciler to use. The default is to use the 'master-count' reconciler which is the default for 1.9 and in use prior to 1.9. The 'lease' reconciler stores endpoints within the storage api for better cleanup of deleted (or removed) API servers. The 'none' reconciler is a no-op reconciler, which can be used in self-hosted environments.   ([#51698](https://github.com/kubernetes/kubernetes/pull/51698), [@rphill...

kustomize, so there are a few backwards-incompatible changes, most of which are rare use cases, bug fixes with side effects, or things that have been deprecated for multiple releases already:
  
  - https://github.com/kubernetes-sigs/kustomize/pull/4911: Drop support for a very old, legacy style of patches. patches used to be allowed to be used as an alias for patchesStrategicMerge in kustomize v3. You now have to use patchesStrategicMerge explicitly, or update to the new syntax supported by patches....

- kubeadm init correctly uses `--node-name` and `--cri-socket` when `--config` option is also used ([#71323](https://github.com/kubernetes/kubernetes/pull/71323), [@bart0sh](https://github.com/bart0sh))
- kubeadm: Always pass spec.nodeName as `--hostname-override` for kube-proxy ([#71283](https://github.com/kubernetes/kubernetes/pull/71283), [@Klaven](https://github.com/Klaven))

  - All resources under `apps/v1beta1` and `apps/v1beta2` - use `apps/v1` instead
  - `daemonsets`, `deployments`, `replicasets` resources under `extensions/v1beta1` - use `apps/v1` instead
  - `networkpolicies` resources under `extensions/v1beta1` - use `networking.k8s.io/v1` instead

- Add support for CEL expressions with escaped names in structured authentication config.  Using `[` for accessing claims or user data is preferred when names contain characters that would need to be escaped.  CEL optionals via `?` can be used in places where `has` cannot be used, i.e. `claims[?"kubernetes.io"]` or `user.extra[?"domain.io/foo"]`. ([#131574](https://github.com/kubernetes/kubernetes/pull/131574), [@enj](https://github.com/enj)) [SIG API Machinery and Auth]...