irreversible.**  To rollback, you must restore from a backup made before the
protobuf/etcd3 switch, and any changes since the backup will be lost.  As 1.5
does not support protobuf encoding, if you roll back to 1.5 after upgrading to
protobuf you will be forced to restore from backup, and you will lose any changes
since you converted to protobuf.  After conversion to protobuf, you should

    - [Client Binaries](#client-binaries-11)
    - [Server Binaries](#server-binaries-11)
    - [Node Binaries](#node-binaries-11)
  - [1.9 Release Notes](#19-release-notes)
  - [WARNING: etcd backup strongly recommended](#warning-etcd-backup-strongly-recommended)
  - [Introduction to 1.9.0](#introduction-to-190)
  - [Major themes](#major-themes)
    - [API Machinery](#api-machinery)
    - [Apps](#apps)
    - [Auth](#auth)

- Kubeadm now includes CoreDNS version 1.6.7 ([#86260](https://github.com/kubernetes/kubernetes/pull/86260), [@rajansandeep](https://github.com/rajansandeep)) [SIG Cluster Lifecycle]
- Kubeadm upgrades always persist the etcd backup for stacked ([#86861](https://github.com/kubernetes/kubernetes/pull/86861), [@SataQiu](https://github.com/SataQiu)) [SIG Cluster Lifecycle]

  - The deprecated `--etcd-quorum-read` flag has been removed. Quorum reads are now always enabled when fetching data from etcd. Remove the `--etcd-quorum-read`...

- The job controller back-off logic is now decoupled from workqueue. In case of parallelism > 1, if there are multiple new failures in a reconciliation cycle, all the failures are taken into account to compute the back-off. Previously, the back-off kicked in for all types of failures; with this change, only pod failures are taken into account. If the back-off limits exceeds, the job is marked as failed immediately; before this change, the...

- `kubeadm`: `crictl pull` should use `-i` to set the image service endpoint. ([#117835](https://github.com/kubernetes/kubernetes/pull/117835), [@pacoxu](https://github.com/pacoxu))
- `kubeadm`: fixed 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))

Additionally, these Kubernetes snapshot primitives act as basic building blocks that unlock the ability to develop advanced, enterprise-grade, storage administration features for Kubernetes: including application or cluster level backup solutions.

- Extended resources backed by DRA feature allowed cluster operator to specify `extendedResourceName` in `DeviceClass`, and application operator to continue using extended resources in pod's requests to request for DRA devices matching the DeviceClass.
  

- When the go-client reflector relists, the ResourceVersion list option is set to the reflector's latest synced resource version to ensure the reflector does not "go back in time" and reprocess events older than it has already processed. If the server responds with an HTTP 410 (Gone) status code response, the relist falls back to using `resourceVersion=""`. ([#83520](https://github.com/kubernetes/kubernetes/pull/83520), [@jpbetz](https://github.com/jpbetz))

 - Fix: support removal of nodes backed by deleted non VMSS instances on Azure ([#91184](https://github.com/kubernetes/kubernetes/pull/91184), [@bpineau](https://github.com/bpineau)) [SIG Cloud Provider]