* Fix metrics API group name in audit configuration ([#53493](https://github.com/kubernetes/kubernetes/pull/53493), [@piosz](https://github.com/piosz))
* GCE: Fixes ILB sync on legacy networks and auto networks with unique subnet names ([#53410](https://github.com/kubernetes/kubernetes/pull/53410), [@nicksardo](https://github.com/nicksardo))

* kubelet: resolved hang/timeout issues when running large numbers of pods with unique configmap/secret references ([#74755](https://github.com/kubernetes/kubernetes/pull/74755), [@liggitt](https://github.com/liggitt))

- The calculation of pod UIDs for static pods has changed to ensure each static pod gets a unique value - this will cause all static pod containers to be recreated/restarted if an in-place kubelet upgrade from 1.20 to 1.21 is performed. Note that draining pods before upgrading the kubelet across minor versions is the supported upgrade path. (...

- CustomResourceDefinition schemas that use `x-kubernetes-list-map-keys` to specify properties that uniquely identify list items must make those properties required or have a default value, to ensure those properties are present for all list items. See https://kubernetes.io/docs/reference/using-api/api-concepts/#merge-strategy for details. ([#88076](ht...

- Change the calculation of pod UIDs so that static pods get a unique value - will cause all containers to be killed and recreated after in-place upgrade. ([#87461](https://github.com/kubernetes/kubernetes/pull/87461), [@bboreham](https://github.com/bboreham)) [SIG Node]

pods need. The most likely error would be a pod set to `Failed` phase with reason set to `OutOfCpu` or `OutOfMemory`, but any resource on the node that has some fixed limit (including persistent volume counts on cloud nodes, exclusive CPU cores, or unique hardware devices) could trigger the failure. While this behavior is correct it reduces the throughput of pod execution and creates user-visible warnings - [future versions of Kubernetes will minimize the likelihood users see pod failures due to this...

* dynamically, which means the cluster will automatically pick a free IP within the configured Service IP range.
* statically, which means the user will set one IP within the configured Service IP range.

Service `ClusterIP` are unique, hence, trying to create a Service with a `ClusterIP` that has already been allocated will return an error.

## Urgent Upgrade Notes

### (No, really, you MUST read this before you upgrade)