- Introduced a new declarative validation tag `+k8s:customUnique` to control listmap uniqueness. ([#134279](https://github.com/kubernetes/kubernetes/pull/134279), [@yongruilin](https://github.com/yongruilin)) [SIG API Machinery and Auth]

  - Added an additional identifier to `ResourceClaim.Status` for the device supports multiple allocations.

- Fixed missing validation of uniqueness of list items in lists with `x-kubernetes-list-type: map` or `x-kubernetes-list-type: set` in CustomResources. ([#84920](https://github.com/kubernetes/kubernetes/pull/84920), [@sttts](https://github.com/sttts)) [SIG API Machinery]

- Certificate handling improvements:
  - Renew certs as part of upgrade.
  - New `kubeadm alpha phase certs renew` command for renewing certificates.
  - Certificates created with kubeadm now have improved uniqueness of Distinguished Name fields.
- HA improvements:
  - `kubeadm join --experimental-control-plane` can now be used to join control plane instances to an existing cluster.

	or it is a <a href="#Struct_types">field name</a> or
	<a href="#MethodName">method name</a>.</li>
</ol>
<p>
All other identifiers are not exported.
</p>

<h3 id="Uniqueness_of_identifiers">Uniqueness of identifiers</h3>

<p>
Given a set of identifiers, an identifier is called <i>unique</i> if it is
<i>different</i> from every other in the set.