### API Change

- Protobuf serialization of metav1.MicroTime timestamps (used in `Lease` and `Event` API objects) has been corrected to truncate to microsecond precision, to match the documented behavior and JSON/YAML serialization. Any existing persisted data is truncated to microsecond when read from etcd. ([#111936](https://github.com/kubernetes/kubernetes/pull/111936), [@haoruan](https://github.com/haoruan)) [SIG API Machinery]

- Kubeadm: enhanced the "patches" functionality to be able to patch kubelet config files containing `v1beta1.KubeletConfiguration`. The new patch target is called `kubeletconfiguration` (e.g. patch file `kubeletconfiguration+json.json`).This makes it possible to apply node specific KubeletConfiguration options during `init`, `join` and `upgrade`, while the main `KubeletConfiguration` that is passed to `init` as part of the `--config` file can still act as the global stored in...

- github.com/evanphx/json-patch: [e83c0a1 → v4.9.0+incompatible](https://github.com/evanphx/json-patch/compare/e83c0a1...v4.9.0)
- github.com/google/cadvisor: [8450c56 → v0.37.0](https://github.com/google/cadvisor/compare/8450c56...v0.37.0)
- github.com/json-iterator/go: [v1.1.9 → v1.1.10](https://github.com/json-iterator/go/compare/v1.1.9...v1.1.10)

this is known to affect is curl when you use -d with JSON but don't set a
content type, helpfully sends "application/x-www-urlencoded", which is not
correct.
Other client authors should double check that you are sending proper
accept and content type headers, or set no value (in which case JSON is the
default).
An example using curl:
<code>curl -H "Content-Type: application/json" -XPOST -d

- The API server now detects and fails on startup if there are conflicting issuers between...

* Removed comments in json config when using kubectl edit with -o json ([#31685](https://github.com/kubernetes/kubernetes/pull/31685), [@jellonek](https://github.com/jellonek))

- the ability to rollback to etcd2 can be preserved by setting the storage media type flag on `kube-apiserver`

  ```
  --storage-media-type application/json
  ```

  to continue to use `application/json` as the storage media type which can be changed to
  `application/vnd.kubernetes.protobuf` at a later time.

## Major updates and release themes

* Fix aggressive VM calls for Azure VMSS ([#83102](https://github.com/kubernetes/kubernetes/pull/83102), [@feiskyer](https://github.com/feiskyer))

API fields previously capable of storing and returning either `[]` and `null` via JSON API requests (for example, the Endpoints `subsets` field)
can now store only `null` when created using the protobuf content-type or stored in etcd using protobuf serialization (the default in 1.6).

  - The /swagger.json and /swagger-2.0.0.pb-v1 schema documents, deprecated since v1.10, have been removed in favor of `/openapi/v2` ([#73148](https://github.com/kubernetes/kubernetes/pull/73148), [@liggitt](https://github.com/liggitt))