Adding a release page under "Release Information"
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Jim Angel
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title: "Release notes and version skew"
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weight: 10
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reviewers:
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- sig-api-machinery
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- sig-architecture
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- sig-cli
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- sig-cluster-lifecycle
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- sig-node
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- sig-release
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title: Kubernetes version and version skew support policy
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content_type: concept
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weight: 30
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---
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<!-- overview -->
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This document describes the maximum version skew supported between various Kubernetes components.
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Specific cluster deployment tools may place additional restrictions on version skew.
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<!-- body -->
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## Supported versions
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Kubernetes versions are expressed as **x.y.z**,
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where **x** is the major version, **y** is the minor version, and **z** is the patch version, following [Semantic Versioning](https://semver.org/) terminology.
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For more information, see [Kubernetes Release Versioning](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/release/versioning.md#kubernetes-release-versioning).
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The Kubernetes project maintains release branches for the most recent three minor releases ({{< skew latestVersion >}}, {{< skew prevMinorVersion >}}, {{< skew oldestMinorVersion >}}). Kubernetes 1.19 and newer receive approximately 1 year of patch support. Kubernetes 1.18 and older received approximately 9 months of patch support.
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Applicable fixes, including security fixes, may be backported to those three release branches, depending on severity and feasibility.
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Patch releases are cut from those branches at a [regular cadence](https://git.k8s.io/sig-release/releases/patch-releases.md#cadence), plus additional urgent releases, when required.
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The [Release Managers](https://git.k8s.io/sig-release/release-managers.md) group owns this decision.
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For more information, see the Kubernetes [patch releases](https://git.k8s.io/sig-release/releases/patch-releases.md) page.
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## Supported version skew
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### kube-apiserver
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In [highly-available (HA) clusters](/docs/setup/production-environment/tools/kubeadm/high-availability/), the newest and oldest `kube-apiserver` instances must be within one minor version.
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Example:
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* newest `kube-apiserver` is at **{{< skew latestVersion >}}**
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* other `kube-apiserver` instances are supported at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}**
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### kubelet
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`kubelet` must not be newer than `kube-apiserver`, and may be up to two minor versions older.
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Example:
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* `kube-apiserver` is at **{{< skew latestVersion >}}**
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* `kubelet` is supported at **{{< skew latestVersion >}}**, **{{< skew prevMinorVersion >}}**, and **{{< skew oldestMinorVersion >}}**
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{{< note >}}
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If version skew exists between `kube-apiserver` instances in an HA cluster, this narrows the allowed `kubelet` versions.
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{{</ note >}}
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Example:
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* `kube-apiserver` instances are at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}**
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* `kubelet` is supported at **{{< skew prevMinorVersion >}}**, and **{{< skew oldestMinorVersion >}}** (**{{< skew latestVersion >}}** is not supported because that would be newer than the `kube-apiserver` instance at version **{{< skew prevMinorVersion >}}**)
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### kube-controller-manager, kube-scheduler, and cloud-controller-manager
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`kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` must not be newer than the `kube-apiserver` instances they communicate with. They are expected to match the `kube-apiserver` minor version, but may be up to one minor version older (to allow live upgrades).
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Example:
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* `kube-apiserver` is at **{{< skew latestVersion >}}**
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* `kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` are supported at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}**
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{{< note >}}
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If version skew exists between `kube-apiserver` instances in an HA cluster, and these components can communicate with any `kube-apiserver` instance in the cluster (for example, via a load balancer), this narrows the allowed versions of these components.
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{{< /note >}}
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Example:
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* `kube-apiserver` instances are at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}**
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* `kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` communicate with a load balancer that can route to any `kube-apiserver` instance
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* `kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` are supported at **{{< skew prevMinorVersion >}}** (**{{< skew latestVersion >}}** is not supported because that would be newer than the `kube-apiserver` instance at version **{{< skew prevMinorVersion >}}**)
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### kubectl
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`kubectl` is supported within one minor version (older or newer) of `kube-apiserver`.
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Example:
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* `kube-apiserver` is at **{{< skew latestVersion >}}**
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* `kubectl` is supported at **{{< skew nextMinorVersion >}}**, **{{< skew latestVersion >}}**, and **{{< skew prevMinorVersion >}}**
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{{< note >}}
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If version skew exists between `kube-apiserver` instances in an HA cluster, this narrows the supported `kubectl` versions.
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{{< /note >}}
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Example:
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* `kube-apiserver` instances are at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}**
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* `kubectl` is supported at **{{< skew latestVersion >}}** and **{{< skew prevMinorVersion >}}** (other versions would be more than one minor version skewed from one of the `kube-apiserver` components)
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## Supported component upgrade order
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The supported version skew between components has implications on the order in which components must be upgraded.
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This section describes the order in which components must be upgraded to transition an existing cluster from version **{{< skew prevMinorVersion >}}** to version **{{< skew latestVersion >}}**.
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### kube-apiserver
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Pre-requisites:
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* In a single-instance cluster, the existing `kube-apiserver` instance is **{{< skew prevMinorVersion >}}**
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* In an HA cluster, all `kube-apiserver` instances are at **{{< skew prevMinorVersion >}}** or **{{< skew latestVersion >}}** (this ensures maximum skew of 1 minor version between the oldest and newest `kube-apiserver` instance)
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* The `kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` instances that communicate with this server are at version **{{< skew prevMinorVersion >}}** (this ensures they are not newer than the existing API server version, and are within 1 minor version of the new API server version)
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* `kubelet` instances on all nodes are at version **{{< skew prevMinorVersion >}}** or **{{< skew oldestMinorVersion >}}** (this ensures they are not newer than the existing API server version, and are within 2 minor versions of the new API server version)
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* Registered admission webhooks are able to handle the data the new `kube-apiserver` instance will send them:
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* `ValidatingWebhookConfiguration` and `MutatingWebhookConfiguration` objects are updated to include any new versions of REST resources added in **{{< skew latestVersion >}}** (or use the [`matchPolicy: Equivalent` option](/docs/reference/access-authn-authz/extensible-admission-controllers/#matching-requests-matchpolicy) available in v1.15+)
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* The webhooks are able to handle any new versions of REST resources that will be sent to them, and any new fields added to existing versions in **{{< skew latestVersion >}}**
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Upgrade `kube-apiserver` to **{{< skew latestVersion >}}**
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{{< note >}}
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Project policies for [API deprecation](/docs/reference/using-api/deprecation-policy/) and
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[API change guidelines](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-architecture/api_changes.md)
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require `kube-apiserver` to not skip minor versions when upgrading, even in single-instance clusters.
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{{< /note >}}
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### kube-controller-manager, kube-scheduler, and cloud-controller-manager
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Pre-requisites:
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* The `kube-apiserver` instances these components communicate with are at **{{< skew latestVersion >}}** (in HA clusters in which these control plane components can communicate with any `kube-apiserver` instance in the cluster, all `kube-apiserver` instances must be upgraded before upgrading these components)
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Upgrade `kube-controller-manager`, `kube-scheduler`, and `cloud-controller-manager` to **{{< skew latestVersion >}}**
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### kubelet
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Pre-requisites:
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* The `kube-apiserver` instances the `kubelet` communicates with are at **{{< skew latestVersion >}}**
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Optionally upgrade `kubelet` instances to **{{< skew latestVersion >}}** (or they can be left at **{{< skew prevMinorVersion >}}** or **{{< skew oldestMinorVersion >}}**)
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{{< note >}}
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Before performing a minor version `kubelet` upgrade, [drain](/docs/tasks/administer-cluster/safely-drain-node/) pods from that node.
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In-place minor version `kubelet` upgrades are not supported.
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{{</ note >}}
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{{< warning >}}
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Running a cluster with `kubelet` instances that are persistently two minor versions behind `kube-apiserver` is not recommended:
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* they must be upgraded within one minor version of `kube-apiserver` before the control plane can be upgraded
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* it increases the likelihood of running `kubelet` versions older than the three maintained minor releases
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{{</ warning >}}
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### kube-proxy
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* `kube-proxy` must be the same minor version as `kubelet` on the node.
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* `kube-proxy` must not be newer than `kube-apiserver`.
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* `kube-proxy` must be at most two minor versions older than `kube-apiserver.`
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Example:
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If `kube-proxy` version is **{{< skew oldestMinorVersion >}}**:
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* `kubelet` version must be at the same minor version as **{{< skew oldestMinorVersion >}}**.
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* `kube-apiserver` version must be between **{{< skew oldestMinorVersion >}}** and **{{< skew latestVersion >}}**, inclusive.
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