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

### API Change

 - For all kinds in the API group version, a spec.selector default value is no longer
 available, because it's incompatible with `kubectl
 apply` and strategic merge patch. You must explicitly set the spec.selector value
 in your manifest. An object with a spec.selector value that does not match the labels in
 its spec.template is invalid.

 - Selector mutation is disabled for all kinds in the

- Introduces new alpha functionality to the reflector, allowing user to enable API streaming.
  
  To activate this feature, users can set the `ENABLE_CLIENT_GO_WATCH_LIST_ALPHA` environmental variable.
  It is important to note that the server must support streaming for this feature to function properly.
  If streaming is not supported by the server, the reflector will revert to the previous method

* Added the ability to select pods in a chosen node to be drained based on given pod label-selector. ([#56864](https://github.com/kubernetes/kubernetes/pull/56864), [@juanvallejo](https://github.com/juanvallejo))

* 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))...

* 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))

* Deployment will stop adding pod-template-hash labels/selector to ReplicaSets and Pods it adopts. Resources created by Deployments are not affected (will still have pod-template-hash labels/selector).  ([#61615](https://github.com/kubernetes/kubernetes/pull/61615), [@janetkuo](https://github.com/janetkuo))

  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]

- 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]