* [alpha] Mount namespace propagation

  * The `VolumeMount.Propagation` field for `VolumeMount` in pod containers is now available.

  * 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.

- Added request header UID propagation, behind an alpha `RemoteRequestHeaderUID` feature gate. ([#129081](https://github.com/kubernetes/kubernetes/pull/129081), [@stalz](https://github.com/stlaz)) [SIG API SIG API Machinery, cluster lifecycle, testing]

### Failing Test

* Azure VMSS: support VM names to contain the `_` character ([#63526](https://github.com/kubernetes/kubernetes/pull/63526), [@djsly](https://github.com/djsly))

Storage Interface (CSI) features](https://github.com/kubernetes/enhancements/issues/178) this quarter in anticipation of moving support for CSI from beta to GA in the next Kubernetes release. This includes graduating the dependent “mount namespace propagation” feature to GA, moving the Kubelet plugin registration mechanism to beta, adding alpha support for a new CSI driver registry as well as for topology, and adding a number of alpha features to support the use of CSI for “local ephemeral volumes” (that...

* kubelet has alpha support for mount propagation. It is disabled by default and it is there for testing only. This feature may be redesigned or even removed in a future release. ([#46444](https://github.com/kubernetes/kubernetes/pull/46444), [@jsafrane](https://github.com/jsafrane))

* Default mount propagation has changed from `HostToContainer` ("rslave" in Linux terminology), as it was in 1.10, to `None` ("private") to match the behavior in 1.9 and earlier releases; `HostToContainer` as a default caused regressions in some pods. If you are relying on...

- Garbage collector now can correctly orphan ControllerRevisions when StatefulSets are deleted with orphan propagation policy. ([#84984](https://github.com/kubernetes/kubernetes/pull/84984), [@cofyc](https://github.com/cofyc)) [SIG Apps]

* Fix a bug that ListOptions.AllowWatchBookmarks wasn't propagating correctly in kube-apiserver. ([#80157](https://github.com/kubernetes/kubernetes/pull/80157), [@wojtek-t](https://github.com/wojtek-t))

- Stop propagating SelfLink (deprecated in 1.16) in kube-apiserver ([#94397](https://github.com/kubernetes/kubernetes/pull/94397), [@wojtek-t](https://github.com/wojtek-t)) [SIG API Machinery and Testing]

- Apiserver: used the correct error when logging errors updating managedFields. ([#113711](https://github.com/kubernetes/kubernetes/pull/113711), [@andrewsykim](https://github.com/andrewsykim))
- Avoided propagating hosts `search .` into containers in `/etc/resolv.conf`. ([#112157](https://github.com/kubernetes/kubernetes/pull/112157), [@dghubble](https://github.com/dghubble))