- Fix controller-manager crashes when flex plugin is removed from flex plugin directory ([#65536](https://github.com/kubernetes/kubernetes/pull/65536), [@gnufied](https://github.com/gnufied))

  * You can now set `VolumeMount.Propagation` to `Bidirectional` to enable a particular mount for a container to propagate itself to the host or other containers.

* [alpha] Improve Flex volume deployment

  * Flex volume driver deployment is simplified in the following ways:

    * New driver files can now be automatically discovered and initialized without requiring a kubelet or controller-manager restart.

- Kubeadm: always mount the kube-controller-manager hostPath volume that is given by the `--flex-volume-plugin-dir` flag. ([#84468](https://github.com/kubernetes/kubernetes/pull/84468), [@neolit123](https://github.com/neolit123))

- Flex volume plugins now support expandvolume (to increase underlying volume capacity) and expanfs (resize filesystem) commands that Flex plugin authors can implement to support expanding in use Flex PersistentVolumes ([#67851](https://github.com/kubernetes/kubernetes/pull/67851), [@aniket-s-kulkarni](https://github.com/aniket-s-kulkarni))

  * If you depend on the old behavior of volumes binding to existing pool of PersistentVolume objects then modify the StorageClass object and set `storageclass.beta.kubernetes.io/is-default-class` to `false`.

or GA.
  * New Flex Volume Plugin enables users to use out-of-process volume plugins that
are installed to “/usr/libexec/kubernetes/kubelet-plugins/volume/exec/” on

* HostAliases is now parsed with `hostAliases` json keys to be in line with the feature's name. ([#47512](https://github.com/kubernetes/kubernetes/pull/47512), [@rickypai](https://github.com/rickypai))

## Urgent Upgrade Notes 

### (No, really, you MUST read this before you upgrade)

- ACTION REQUIRED: Switch core master base images (kube-controller-manager) from debian to distroless. If you need Flex Volumes support using scripts, please build your own image with required packages (like bash) ([#91329](https://github.com/kubernetes/kubernetes/pull/91329), [@dims](https://github.com/dims)) [SIG Cloud Provider, Release, Storage and Testing]