- Adds `\livez` for liveness health checking for kube-apiserver. Using the parameter `--maximum-startup-sequence-duration` will allow the liveness endpoint to defer boot-sequence failures for the specified duration period. ([#81969](https://github.com/kubernetes/kubernetes/pull/81969), [@logicalhan](https://github.com/logicalhan))

- Add flag --lease-reuse-duration-seconds for kube-apiserver to config etcd lease reuse duration. ([#97009](https://github.com/kubernetes/kubernetes/pull/97009), [@lingsamuel](https://github.com/lingsamuel)) [SIG API Machinery and Scalability]

   ([#122830](https://github.com/kubernetes/kubernetes/pull/122830), [@p0lyn0mial](https://github.com/p0lyn0mial))
- Updated `ImageGCMaxAge` behavior in the kubelet to wait the `MaxAge` duration after the kubelet has restarted before garbage collecting.
   ([#123343](https://github.com/kubernetes/kubernetes/pull/123343), [@haircommander](https://github.com/haircommander))

* Kubeadm now includes CoreDNS version 1.6.5 ([#85108](https://github.com/kubernetes/kubernetes/pull/85108), [@rajansandeep](https://github.com/rajansandeep))
    *  - `kubernetes` plugin adds metrics to measure kubernetes control plane latency.
    *  -  the `health` plugin now includes the `lameduck` option by default, which waits for a duration before shutting down.

#### Application autoscaling
* Make "upscale forbidden window" and "downscale forbidden window"  duration configurable in arguments of kube-controller-manager. ([#42101](https://github.com/kubernetes/kubernetes/pull/42101), [@Dmitry1987](https://github.com/Dmitry1987))

#### Application Deployment

- 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))

- `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))

* 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

- 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))

- 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...