* [beta] Kubelet certificate rotation through the certificates API has been promoted from alpha to beta. RBAC cluster roles for the certificates controller have been added for common uses of the certificates API, such as the kubelet's.

### Cluster Lifecycle

- Added two client certificate metrics for exec auth:
    - `rest_client_certificate_expiration_seconds` a gauge reporting the lifetime of the current client certificate. Reports the time of expiry in seconds since January 1, 1970 UTC.

Prior to 1.17 and for existing nodes created by `kubeadm init` where kubelet client certificate rotation is desired, you must modify `/etc/kubernetes/kubelet.conf` to point to the PEM symlink for rotation:

  - [WARNING: etcd backup strongly recommended](#warning-etcd-backup-strongly-recommended)
  - [Major updates and release themes](#major-updates-and-release-themes)
  - [Action Required](#action-required-1)
    - [Certificates API](#certificates-api)
    - [Cluster Autoscaler](#cluster-autoscaler)
    - [Deployment](#deployment)
    - [Federation](#federation)
    - [Internal Storage Layer](#internal-storage-layer)

* kubeadm: preflight checks on external etcd certificates are now skipped when joining a control-plane node with automatic copy of cluster certificates (--certificate-key) ([#75847](https://github.com/kubernetes/kubernetes/pull/75847), [@fabriziopandini](https://github.com/fabriziopandini))

previously created the first bootstrap client credentials in the certificates directory as `kubelet-client.key` and `kubelet-client.crt`.  Subsequent certificates created by cert rotation were created in a combined PEM file that was atomically rotated as `kubelet-client-DATE.pem` in that directory, which meant clients relying on the `node.kubeconfig` generated by bootstrapping would never use a rotated cert.  The initial bootstrap certificate is now generated into the cert directory as a PEM file and symlinked...

- When `--rotate-server-certificates` is enabled, kubelet will no longer request a new certificate on startup if the current certificate on disk is satisfactory. ([#69991](https://github.com/kubernetes/kubernetes/pull/69991), [@agunnerson-ibm](https://github.com/agunnerson-ibm))

- Kubeadm: during execution of the "check expiration" command, treat the etcd CA as external if there is a missing etcd CA key file (etcd/ca.key) and perform the proper validation on certificates signed by the etcd CA. Additionally, make sure that the CA for all...

        * requests from a node for a TLS serving certificate for itself are approved if the CSR creator has `create` permission on the `certificatesigningrequests` resource and the `selfnodeserver` subresource in the `certificates.k8s.io` API group