- The kube-controller-manager's deprecated `--experimental-cluster-signing-duration` flag is now removed. Adapt your machinery to use the `--cluster-signing-duration` flag that is available since v1.19. ([#108476](https://github.com/kubernetes/kubernetes/pull/108476), [@ialidzhikov](https://github.com/ialidzhikov))

- Kube-controller-manager: the `--experimental-cluster-signing-duration` flag is marked as deprecated for removal in v1.22, and is replaced with `--cluster-signing-duration`. ([#91154](https://github.com/kubernetes/kubernetes/pull/91154), [@liggitt](https://github.com/liggitt)) [SIG Auth and Cloud Provider]

			err = z.Init(ctx) // Initializes all pools.
		})
		if err != nil {
			if !configRetriableErrors(err) {
				logger.Fatal(err, "Unable to initialize backend")
			}
			retry := time.Duration(r.Float64() * float64(5*time.Second))
			storageLogIf(ctx, fmt.Errorf("Unable to initialize backend: %w, retrying in %s", err, retry))
			time.Sleep(retry)
			attempt++
			continue
		}
		break
	}

- `watch.Until` now works for long durations. ([#67350](https://github.com/kubernetes/kubernetes/pull/67350), [@tnozicka](https://github.com/tnozicka))
- Added duration metric for CRD webhook converters. ([#74376](https://github.com/kubernetes/kubernetes/pull/74376), [@mbohlool](https://github.com/mbohlool))

		HTTPStatusCode: http.StatusConflict,
	},
	ErrInvalidDuration: {
		Code:           "InvalidDuration",
		Description:    "Duration provided in the request is invalid.",
		HTTPStatusCode: http.StatusBadRequest,
	},
	ErrInvalidBucketObjectLockConfiguration: {
		Code:           "InvalidRequest",

* Added kubeadm commands to manage bootstrap tokens and the duration they are valid for. ([#35805](https://github.com/kubernetes/kubernetes/pull/35805), [@dgoodwin](https://github.com/dgoodwin))

### kubectl

#### New Commands

- kubelet: Users can now enable the alpha NodeLease feature gate to have the Kubelet create and periodically renew a Lease in the kube-node-lease namespace. The lease duration defaults to 40s, and can be configured via the kubelet.config.k8s.io/v1beta1.KubeletConfiguration's NodeLeaseDurationSeconds field. ([#66257](https://github.com/kubernetes/kubernetes/pull/66257), [@mtaufen](https://github.com/mtaufen)) Courtesy of...

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- The `CertificateSigningRequest.certificates.k8s.io` API supports an optional expirationSeconds field to allow the client to request a particular duration for the issued certificate.  The default signer implementations provided by the Kubernetes controller manager will honor this field as long as it does not exceed the --cluster-signing-duration flag. ([#99494](https://github.com/kubernetes/kubernetes/pull/99494), [@enj](https://github.com/enj))

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