- Adopted a new implementation of watch caches for **list** verbs, using a btree data structure. The new implementation is active by default; you can opt out by disabling the `BtreeWatchCache` feature gate. ([#128415](https://github.com/kubernetes/kubernetes/pull/128415), [@serathius](https://github.com/serathius)) [SIG API Machinery, Auth...

but are otherwise ignored.
</p>

<pre>
struct {
	x, y float64 ""  // an empty tag string is like an absent tag
	name string  "any string is permitted as a tag"
	_    [4]byte "ceci n'est pas un champ de structure"
}

// A struct corresponding to a TimeStamp protocol buffer.
// The tag strings define the protocol buffer field numbers;
// they follow the convention outlined by the reflect package.
struct {

- kubeadm: JoinConfiguration now houses the discovery options in a nested Discovery structure, which in turn has a couple of other nested structures to house more specific options (BootstrapTokenDiscovery and FileDiscovery) ([#67763](https://github.com/kubernetes/kubernetes/pull/67763), [@rosti](https://github.com/rosti))

It is likely that `v1alpha2` will be removed in one of the future Kubernetes releases to be able to develop `v1`.

### Structured logging graduate to Beta

Structured logging reached its Beta milestone. Most log messages from kubelet and kube-scheduler have been converted. Users are encouraged to try out JSON output or parsing of the structured text format and provide feedback on possible solutions for the open issues, such as handling of multi-line strings in log values.

 ([#64792](https://github.com/kubernetes/kubernetes/pull/64792), [@luxas](https://github.com/luxas))

### Structured Logging in Kubelet

   ([#123384](https://github.com/kubernetes/kubernetes/pull/123384), [@aleksandra-malinowska](https://github.com/aleksandra-malinowska))
- In kubeadm, in the new output API 'output.kubeadm.k8s.io/v1alpha3', the UpgradePlan structure that is used when calling 'kubeadm upgrade plan ... -o yaml|json' was modified to include a list of multiple available upgrades.
   ([#123461](https://github.com/kubernetes/kubernetes/pull/123461), [@carlory](https://github.com/carlory))

## **Action Required Before Upgrading**

### Network

- Migrate `volume/csi/csi-client.go` logs to structured logging. ([#99441](https://github.com/kubernetes/kubernetes/pull/99441), [@CKchen0726](https://github.com/CKchen0726))
- Migrate statefulset files to structured logging ([#106109](https://github.com/kubernetes/kubernetes/pull/106109), [@h4ghhh](https://github.com/h4ghhh))

- Fixed code-generator client-gen to work with `api/v1`-like package structure. ([#125162](https://github.com/kubernetes/kubernetes/pull/125162), [@sttts](https://github.com/sttts)) [SIG API Machinery and Apps]