- 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.

	AssertEqual(t, false, DB.Migrator().HasIndex(&UniqueTest{}, "name"))
	AssertEqual(t, false, DB.Migrator().HasIndex(&UniqueTest{}, "name_1"))
	AssertEqual(t, false, DB.Migrator().HasIndex(&UniqueTest{}, "name_2"))

	ct, err = findColumnType(&UniqueTest{}, "name")
	if err != nil {
		t.Fatalf("findColumnType err:%v", err)
	}

	value, ok = ct.DefaultValue()
	AssertEqual(t, "", value)

- 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]