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`...

- `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))

  Ensures fallback to OpenAPI V2 endpoint for errors retrieving OpenAPI V3 document. ([#117918](https://github.com/kubernetes/kubernetes/pull/117918), [@seans3](https://github.com/seans3)) [SIG CLI]
- 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]

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.

- Update `kube-proxy` base image `debian-iptables` to v1.6.2 to pickup [documentation](https://github.com/kubernetes/release/pull/2106)