Some upgrade methods might upgrade etcd from 3.0 to 3.1 automatically when you upgrade from Kubernetes 1.8, unless you specify otherwise. Because [etcd does not support downgrading](https://coreos.com/etcd/docs/latest/upgrades/upgrade_3_1.html), you'll need to either remain on etcd 3.1 or restore from a backup if you want to downgrade back to Kubernetes 1.8.

    - [Node Binaries](#node-binaries)
    - [Container Images](#container-images)
  - [Changelog since v1.34.0](#changelog-since-v1340)
  - [Urgent Upgrade Notes](#urgent-upgrade-notes)
    - [(No, really, you MUST read this before you upgrade)](#no-really-you-must-read-this-before-you-upgrade)
  - [Changes by Kind](#changes-by-kind)
    - [Deprecation](#deprecation)
    - [API Change](#api-change)
    - [Feature](#feature)

- Rev the Azure SDK for networking to 2017-06-01 ([#61955](https://github.com/kubernetes/kubernetes/pull/61955))
- Es-image has been upgraded to Elasticsearch 6.3.2 ([#67484](https://github.com/kubernetes/kubernetes/pull/67484))
- metrics-server has been upgraded to v0.3.1. ([#68746](https://github.com/kubernetes/kubernetes/pull/68746))
- GLBC has been updated to v1.2.3 ([#66793](https://github.com/kubernetes/kubernetes/pull/66793))

    - [Node Binaries](#node-binaries-12)
- [Kubernetes 1.13 Release Notes](#kubernetes-113-release-notes)
  - [Security Content](#security-content)
  - [Urgent Upgrade Notes](#urgent-upgrade-notes)
    - [(No, really, you MUST do this before you upgrade)](#no-really-you-must-do-this-before-you-upgrade)
  - [Known Issues](#known-issues)
  - [Deprecations](#deprecations)
  - [Major Themes](#major-themes)
    - [SIG API Machinery](#sig-api-machinery)

- kubeadm: `kubeadm upgrade node` now supports `addon` and `post-upgrade` phases. Users can use `kubeadm upgrade node phase addon` to execute the addon upgrade, or use `kubeadm upgrade node --skip-phases addon` to skip the addon upgrade. If you were previously skipping an addon subphase on `kubeadm init` you should now skip the same addon when calling `kubeadm upgrade apply` and `kubeadm upgrade node`. Currently, the `post-upgrade` phase is no-op, and it is mainly used to handle some release-specific...

Updates][major_versions].

This release obsoletes OkHttp 2.x, and all code that uses OkHttp's
`com.squareup.okhttp` package should upgrade to the `okhttp3` package. Libraries
that depend on OkHttp should upgrade quickly to prevent applications from being
stuck on the old version.

 *  **There is no longer a global singleton connection pool.** In OkHttp 2.x,

* **Tolerations**

    - [Additional Notable Feature Updates](#additional-notable-feature-updates)
  - [Known Issues](#known-issues)
  - [Urgent Upgrade Notes](#urgent-upgrade-notes)
    - [(No, really, you MUST read this before you upgrade)](#no-really-you-must-read-this-before-you-upgrade)
      - [API Machinery](#api-machinery)
      - [Apps](#apps)
      - [Auth](#auth)
      - [AWS](#aws)
      - [Azure](#azure)

* kubeadm upgrade no longer races leading to unexpected upgrade behavior on pod restarts ([#62655](https://github.com/kubernetes/kubernetes/pull/62655), [@stealthybox](https://github.com/stealthybox))
    * kubeadm upgrade now successfully upgrades etcd and the controlplane to use TLS
    * kubeadm upgrade now supports external etcd setups
    * kubeadm upgrade can now rollback and restore etcd after an upgrade failure

are hence enabled by default. This will be fixed in a future release.
[#38593](https://github.com/kubernetes/kubernetes/issues/38593)
* Federation control plane can be upgraded by updating the image
fields in the `Deployment` specs of the control plane components.
However, federation control plane upgrades were not tested in this
release [38537](https://github.com/kubernetes/kubernetes/issues/38537)

## Notable Changes to Existing Behavior