### Instrumentation

- Kubeadm: fix a bug where file copy(backup) could not be executed correctly on Windows platform during upgrade ([#117861](https://github.com/kubernetes/kubernetes/pull/117861), [@SataQiu](https://github.com/SataQiu)) [SIG Cluster Lifecycle]

- Kubeadm: during execution of the "check expiration" command, treat the etcd CA as external if there is a missing etcd CA key file (etcd/ca.key) and perform the proper validation on certificates signed by the etcd CA. Additionally, make sure that the CA for all entries...

## Known Issues

* If you need to downgrade from 1.10 to 1.9.x, downgrade to v1.9.6 to ensure PV and PVC objects can be deleted properly.

* fix data loss issue if using existing azure disk with partitions in disk mount  ([#63270](https://github.com/kubernetes/kubernetes/pull/63270), [@andyzhangx](https://github.com/andyzhangx))
* Fixed API server panic during concurrent GET or LIST requests with non-empty `resourceVersion`. ([#65092](https://github.com/kubernetes/kubernetes/pull/65092), [@sttts](https://github.com/sttts))

- Fixed the disruption controller's PDB status synchronization to maintain all PDB conditions during an update. ([#122056](https://github.com/kubernetes/kubernetes/pull/122056), [@dhenkel92](https://github.com/dhenkel92)) [SIG Apps]

- Remove ready file and its directory (which is created during volume SetUp) during emptyDir volume TearDown. ([#95770](https://github.com/kubernetes/kubernetes/pull/95770), [@jingxu97](https://github.com/jingxu97)) [SIG Storage]

### Other (Cleanup or Flake)

- Kubeadm: warn but do not error out on missing "ca.key" files for root CA, front-proxy CA and etcd CA, during "kubeadm join --control-plane" if the user has provided all certificates, keys and kubeconfig files which require signing with the given CA keys. ([#94988](https://github.com/kubernetes/kubernetes/pull/94988), [@neolit123](https://github.com/neolit123))...

* Fixes issue where subpath volume content was deleted during orphaned pod cleanup for Local volumes that are directories (and not mount points) on the root filesystem. ([#72291](https://github.com/kubernetes/kubernetes/pull/72291), [@msau42](https://github.com/msau42))

correct these files before upgrading.** When specifying keys in JSON resource definitions during direct API server communication, the keys are case-sensitive. A bug introduced in Kubernetes 1.8 caused the API server to accept a request with incorrect case and coerce it to correct case, but this behaviour has been fixed in 1.11 and the API server will once again be enforcing the correct case. It’s worth noting that during this time, the `kubectl` tool continued to enforce case-sensitive keys, so users that...