* kube-apiserver: requests to endpoints handled by unavailable extension API servers (as indicated by an `Available` condition of `false` in the registered APIService) now return `503` errors instead of `404` errors. ([#58070](https://github.com/kubernetes/kubernetes/pull/58070), [@weekface](https://github.com/weekface))

### Other notable changes

- The 404 request handler for the GCE Ingress load balancer now exports prometheus metrics, including:

  - `http_404_request_total` (the number of 404 requests handled)
  - `http_404_request_duration_ms` (the amount of time the server took to respond in ms)

- Fixed an issue with stuck connections handling error responses ([#71412](https://github.com/kubernetes/kubernetes/pull/71412), [@liggitt](https://github.com/liggitt))
- apiserver: fixed handling and logging of panics in REST handlers ([#71076](https://github.com/kubernetes/kubernetes/pull/71076), [@liggitt](https://github.com/liggitt))

- Sync node status during kubelet node shutdown.
  Adds an pod admission handler that rejects new pods when the node is in progress of shutting down. ([#98005](https://github.com/kubernetes/kubernetes/pull/98005), [@wzshiming](https://github.com/wzshiming)) [SIG Node]

* Default resourceGroup should be used when the value of annotation azure-load-balancer-resource-group is an empty string. ([#79514](https://github.com/kubernetes/kubernetes/pull/79514), [@feiskyer](https://github.com/feiskyer))
* The CRD handler now properly re-creates stale CR storage to reflect CRD update. ([#79114](https://github.com/kubernetes/kubernetes/pull/79114), [@roycaihw](https://github.com/roycaihw))

- 'Container `preStop` and `postStart` lifecycle handlers using `httpGet` now
  honor the specified `scheme` and `headers` fields. This enables setting custom
  headers and changing the scheme to `HTTPS`, consistent with container
  startup/readiness/liveness probe capabilities. Lifecycle handlers configured
  with `scheme: HTTPS` that encounter errors indicating the endpoint is actually

- `Scheduler` now registers event handlers dynamically. ([#101394](https://github.com/kubernetes/kubernetes/pull/101394), [@Huang-Wei](https://github.com/Huang-Wei))
- `kubectl`: Enable using protocol buffers to request Metrics API. ([#102039](https://github.com/kubernetes/kubernetes/pull/102039), [@serathius](https://github.com/serathius))

    * Introduce a RuntimeClass v1beta1 API. This new beta API renames `runtimeHandler` to `handler`, makes it a required field, and cuts out the spec (handler is a top-level field).

### Bug or Regression

- Fix missing delete events on informer re-lists to ensure all delete events are correctly emitted and using the latest known object state, so that all event handlers and stores always reflect the actual apiserver state as best as possible ([#115901](https://github.com/kubernetes/kubernetes/pull/115901), [@odinuge](https://github.com/odinuge)) [SIG API Machinery]