* 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.

- 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))

## 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]

* 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))