* Added liveness probe to Heapster service. ([#31878](https://github.com/kubernetes/kubernetes/pull/31878), [@mksalawa](https://github.com/mksalawa))
* Adding clusters to the list of valid resources printed by kubectl help ([#31719](https://github.com/kubernetes/kubernetes/pull/31719), [@nikhiljindal](https://github.com/nikhiljindal))

- Kubeadm: a new command `kubeadm alpha certs check-expiration` was created in order to help users in managing expiration for local PKI certificates ([#77863](https://github.com/kubernetes/kubernetes/pull/77863), [@fabriziopandini](https://github.com/fabriziopandini))

### Misc

* Pre-existing log files are now opened with O_APPEND, instead of O_TRUNC. This helps prevent losing logs when components crash-loop, and also enables external log rotation utilities to truncate log files in-place without components extending log files to their pre-truncation sizes on subsequent writes. ([#74837](https://github.com...

- Kube-controller-manager's help will include controllers behind a feature gate in `--controllers` flag ([#120371](https://github.com/kubernetes/kubernetes/pull/120371), [@atiratree](https://github.com/atiratree)) [SIG API Machinery]

* Trusty: Avoid reaching GCE custom metadata size limit ([#22818](https://github.com/kubernetes/kubernetes/pull/22818), [@andyzheng0831](https://github.com/andyzheng0831))
* Update kubectl help for 1.2 resources ([#23305](https://github.com/kubernetes/kubernetes/pull/23305), [@janetkuo](https://github.com/janetkuo))

- K8s.io/component-base/logs: usage of the pflag values in a normal Go flag set led to panics when printing the help message ([#114680](https://github.com/kubernetes/kubernetes/pull/114680), [@pohly](https://github.com/pohly)) [SIG Instrumentation]

### Feature

* Trusty: Avoid reaching GCE custom metadata size limit ([#22818](https://github.com/kubernetes/kubernetes/pull/22818), [@andyzheng0831](https://github.com/andyzheng0831))
* Update kubectl help for 1.2 resources ([#23305](https://github.com/kubernetes/kubernetes/pull/23305), [@janetkuo](https://github.com/janetkuo))

    * When using an in-cluster client with an empty configuration, the `--namespace` flag is now honored ([#46299](https://github.com/kubernetes/kubernetes/pull/46299), [@ncdc](https://github.com/ncdc))

    * The help message for missingResourceError is now generic ([#45582](https://github.com/kubernetes/kubernetes/pull/45582), [@CaoShuFeng](https://github.com/CaoShuFeng))