* Quota admission configuration api graduated to v1beta1 ([#66156](https://github.com/kubernetes/kubernetes/pull/66156), [@vikaschoudhary16](https://github.com/vikaschoudhary16))

 selector mutation in
 a consistent way. This restriction may be lifted in the future, but
 it is likely that that selectors will remain immutable after the move to v1.
 You can continue to use code that depends on mutable selectors by calling
 the apps/v1beta1 API in this release, but you should start planning for code
 that does not depend on mutable selectors.

ReplicationController, but its [selector](http://kubernetes.io/docs/user-guide/labels/#label-selectors) is more general (supports set-based selector; whereas ReplicationController
only supports equality-based selector).
  * Scale subresource support is now expanded to ReplicaSets along with
ReplicationControllers and Deployments. Scale now supports two different types

- Improving the performance of Endpoint and EndpointSlice controllers by caching Service Selectors ([#84280](https://github.com/kubernetes/kubernetes/pull/84280), [@gongguan](https://github.com/gongguan))

- Kube-apiserver: fixed a bug returning inconsistent results from list requests which set a field or label selector and set a paging limit ([#94002](https://github.com/kubernetes/kubernetes/pull/94002), [@wojtek-t](https://github.com/wojtek-t)) [SIG API Machinery]

  IPv6 IPs. ([#121008](https://github.com/kubernetes/kubernetes/pull/121008), [@danwinship](https://github.com/danwinship)) [SIG Network]
- Fixed an issue to not drain all the pods in a namespace when an empty-selector i.e. "{}" is specified in a Pod Disruption Budget (PDB) ([#121131](https://github.com/kubernetes/kubernetes/pull/121131), [@sairameshv](https://github.com/sairameshv)) [SIG Apps]

* For Deployment, ReplicaSet, and DaemonSet, selectors are now immutable when updating via the new `apps/v1beta2` API. For backward compatibility, selectors can still be changed when updating via `apps/v1beta1` or `extensions/v1beta1`. ([#50719](https://github.com/kubernetes/kubernetes/pull/50719), [@crimsonfaith91](https://github.com/crimsonfaith91))...

* Fix StatefulSet to work correctly with set-based selectors. ([#59365](https://github.com/kubernetes/kubernetes/pull/59365), [@ayushpateria](https://github.com/ayushpateria))

### API Change

* restore ability to run against secured etcd ([#21535](https://github.com/kubernetes/kubernetes/pull/21535), [@AdoHe](https://github.com/AdoHe))

### Other notable changes

* validate that daemonsets don't have empty selectors on creation ([#23530](https://github.com/kubernetes/kubernetes/pull/23530), [@mikedanese](https://github.com/mikedanese))