- Fixed a bug where containers would not start on `cgroupv2` systems where `swap` is disabled. ([#120784](https://github.com/kubernetes/kubernetes/pull/120784), [@elezar](https://github.com/elezar))

  Plugin `SelectorSpread` is removed in v1. ([#110534](https://github.com/kubernetes/kubernetes/pull/110534), [@kerthcet](https://github.com/kerthcet))

### CSI Health Monitoring

The CSI health monitoring feature is being released as a second Alpha in Kubernetes 1.21. This feature enables CSI Drivers to share abnormal volume conditions from the underlying storage systems with Kubernetes so that they can be reported as events on PVCs or Pods. This feature serves as a stepping stone towards programmatic detection and resolution of individual volume health issues by Kubernetes.

## Known Issues

  - Expose `--max-nodes-total` as a metric
  - Errors in `IncreaseSize` changed from type `apiError` to `cloudProviderError`
  - Make `build-in-docker` and `test-in-docker` work on Linux systems with SELinux enabled
  - Fix an error where existing nodes were not considered as destinations while finding place for pods in scale-down simulations
  - Remove redundant log lines and reduce severity around parsing kubeEnv

- Until this release, the iscsi plugin was waiting 10 seconds for a path to appear in the device list. However this timeout is not enough, or is less than the default device discovery timeout in most systems, which prevents certain devices from being discovered. This timeout has been raised to 30 seconds, which should help to avoid mount issues due to device discovery. ([#78475](https://github.com/kubernetes/kubernetes/pull/78475), [@humblec](https:/...

### Serverside Apply - Beta 2

With CSI the Kubernetes volume layer becomes truly extensible, allowing third party storage developers to write drivers making their storage systems available in Kubernetes without having to touch the core code.

CSI was first introduction as alpha in Kubernetes v1.9 and moved to beta in Kubernetes v1.10.

  See https://github.com/kubernetes/kubernetes/issues/102750. ([#103231](https://github.com/kubernetes/kubernetes/pull/103231), [@n4j](https://github.com/n4j))
- Fixed applying of SELinux labels to CSI volumes on very busy systems (with "error checking for SELinux support: could not get consistent content of /proc/self/mountinfo after 3 attempts") ([#105934](https://github.com/kubernetes/kubernetes/pull/105934), [@jsafrane](https://github.com/jsafrane)) [SIG Storage]

### Bug or Regression

- Bump system-validators to v1.9.2: remove version-specific cgroup kernel config checks to avoid false failures on cgroup v2 systems when v1-only configs are missing. ([#134090](https://github.com/kubernetes/kubernetes/pull/134090), [@pacoxu](https://github.com/pacoxu)) [SIG Cluster Lifecycle]

* Fix kube-controller-manager panic while provisioning Azure security group rules ([#64739](https://github.com/kubernetes/kubernetes/pull/64739), [@feiskyer](https://github.com/feiskyer))
* Fixes issue for readOnly subpath mounts for SELinux systems and when the volume mountPath already existed in the container image. ([#64351](https://github.com/kubernetes/kubernetes/pull/64351), [@msau42](https://github.com/msau42))