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Upgrading kubeadm clusters from 1.7 to 1.8

This guide is for upgrading kubeadm clusters from version 1.7.x to 1.8.x, as well as 1.7.x to 1.7.y and 1.8.x to 1.8.y where y > x. See also upgrading kubeadm clusters from 1.6 to 1.7 if you’re on a 1.6 cluster currently.

Before you begin
Upgrading your control plane
Upgrading your master and node packages
Recovering from a bad state

Before you begin

Before proceeding:

You need to have a functional kubeadm Kubernetes cluster running version 1.7.0 or higher in order to use the process described here.
Make sure you read the release notes carefully.
As kubeadm upgrade does not upgrade etcd make sure to back it up. You can, for example, use etcdctl backup to take care of this.
Note that kubeadm upgrade will not touch any of your workloads, only Kubernetes-internal components. As a best-practice you should back up what’s important to you. For example, any app-level state, such as a database an app might depend on (like MySQL or MongoDB) must be backed up beforehand.

Also, note that only one minor version upgrade is supported. That is, you can only upgrade from, say 1.7 to 1.8, not from 1.7 to 1.9.

Upgrading your control plane

You have to carry out the following steps by executing these commands on your master node:

Install the most recent version of kubeadm using curl like so:

export VERSION=$(curl -sSL https://dl.k8s.io/release/stable.txt) # or manually specify a released Kubernetes version
export ARCH=amd64 # or: arm, arm64, ppc64le, s390x
curl -sSL https://dl.k8s.io/release/${VERSION}/bin/linux/${ARCH}/kubeadm > /usr/bin/kubeadm
chmod a+rx /usr/bin/kubeadm
Caution: Upgrading the kubeadm package on your system prior to upgrading the control plane causes a failed upgrade. Even though kubeadm is shipped in the Kubernetes repositories, it’s important to install kubeadm manually. The kubeadm team is working on fixing this limitation.

Verify that this download of kubeadm works, and has the expected version:

kubeadm version

If this the first time you use kubeadm upgrade, in order to preserve the configuration for future upgrades, do:

Note that for below you will need to recall what CLI args you passed to kubeadm init the first time.

If you used flags, do:

kubeadm config upload from-flags [flags]

Where flags can be empty.

If you used a config file, do:

kubeadm config upload from-file --config [config]

Where the config is mandatory.

On the master node, run the following:

kubeadm upgrade plan

You should see output similar to this:

[preflight] Running pre-flight checks
[upgrade] Making sure the cluster is healthy:
[upgrade/health] Checking API Server health: Healthy
[upgrade/health] Checking Node health: All Nodes are healthy
[upgrade/health] Checking Static Pod manifests exists on disk: All manifests exist on disk
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[upgrade] Fetching available versions to upgrade to:
[upgrade/versions] Cluster version: v1.7.1
[upgrade/versions] kubeadm version: v1.8.0
[upgrade/versions] Latest stable version: v1.8.0
[upgrade/versions] Latest version in the v1.7 series: v1.7.6

Components that must be upgraded manually after you've upgraded the control plane with 'kubeadm upgrade apply':
COMPONENT   CURRENT      AVAILABLE
Kubelet     1 x v1.7.1   v1.7.6

Upgrade to the latest version in the v1.7 series:

COMPONENT            CURRENT   AVAILABLE
API Server           v1.7.1    v1.7.6
Controller Manager   v1.7.1    v1.7.6
Scheduler            v1.7.1    v1.7.6
Kube Proxy           v1.7.1    v1.7.6
Kube DNS             1.14.4    1.14.4

You can now apply the upgrade by executing the following command:

	kubeadm upgrade apply v1.7.6

_____________________________________________________________________

Components that must be upgraded manually after you've upgraded the control plane with 'kubeadm upgrade apply':
COMPONENT   CURRENT      AVAILABLE
Kubelet     1 x v1.7.1   v1.8.0

Upgrade to the latest stable version:

COMPONENT            CURRENT   AVAILABLE
API Server           v1.7.1    v1.8.0
Controller Manager   v1.7.1    v1.8.0
Scheduler            v1.7.1    v1.8.0
Kube Proxy           v1.7.1    v1.8.0
Kube DNS             1.14.4    1.14.4

You can now apply the upgrade by executing the following command:

	kubeadm upgrade apply v1.8.0

Note: Before you do can perform this upgrade, you have to update kubeadm to v1.8.0

_____________________________________________________________________

The kubeadm upgrade plan checks that your cluster is in an upgradeable state and fetches the versions available to upgrade to in an user-friendly way.

Pick a version to upgrade to and run, for example, kubeadm upgrade apply as follows:

kubeadm upgrade apply v1.8.0

You should see output similar to this:

[preflight] Running pre-flight checks
[upgrade] Making sure the cluster is healthy:
[upgrade/health] Checking API Server health: Healthy
[upgrade/health] Checking Node health: All Nodes are healthy
[upgrade/health] Checking Static Pod manifests exists on disk: All manifests exist on disk
[upgrade/config] Making sure the configuration is correct:
[upgrade/config] Reading configuration from the cluster...
[upgrade/config] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'
[upgrade/version] You have chosen to upgrade to version "v1.8.0"
[upgrade/versions] Cluster version: v1.7.1
[upgrade/versions] kubeadm version: v1.8.0
[upgrade/prepull] Will prepull images for components [kube-apiserver kube-controller-manager kube-scheduler]
[upgrade/prepull] Prepulling image for component kube-scheduler.
[upgrade/prepull] Prepulling image for component kube-apiserver.
[upgrade/prepull] Prepulling image for component kube-controller-manager.
[apiclient] Found 0 Pods for label selector k8s-app=upgrade-prepull-kube-scheduler
[apiclient] Found 1 Pods for label selector k8s-app=upgrade-prepull-kube-scheduler
[apiclient] Found 1 Pods for label selector k8s-app=upgrade-prepull-kube-apiserver
[apiclient] Found 1 Pods for label selector k8s-app=upgrade-prepull-kube-controller-manager
[upgrade/prepull] Prepulled image for component kube-apiserver.
[upgrade/prepull] Prepulled image for component kube-controller-manager.
[upgrade/prepull] Prepulled image for component kube-scheduler.
[upgrade/prepull] Successfully prepulled the images for all the control plane components
[upgrade/apply] Upgrading your Static Pod-hosted control plane to version "v1.8.0"...
[upgrade/staticpods] Writing upgraded Static Pod manifests to "/etc/kubernetes/tmp/kubeadm-upgraded-manifests432902769"
[controlplane] Wrote Static Pod manifest for component kube-apiserver to "/etc/kubernetes/tmp/kubeadm-upgraded-manifests432902769/kube-apiserver.yaml"
[controlplane] Wrote Static Pod manifest for component kube-controller-manager to "/etc/kubernetes/tmp/kubeadm-upgraded-manifests432902769/kube-controller-manager.yaml"
[controlplane] Wrote Static Pod manifest for component kube-scheduler to "/etc/kubernetes/tmp/kubeadm-upgraded-manifests432902769/kube-scheduler.yaml"
[upgrade/staticpods] Moved upgraded manifest to "/etc/kubernetes/manifests/kube-apiserver.yaml" and backed up old manifest to "/etc/kubernetes/tmp/kubeadm-backup-manifests155856668/kube-apiserver.yaml"
[upgrade/staticpods] Waiting for the kubelet to restart the component
[apiclient] Found 1 Pods for label selector component=kube-apiserver
[upgrade/staticpods] Component "kube-apiserver" upgraded successfully!
[upgrade/staticpods] Moved upgraded manifest to "/etc/kubernetes/manifests/kube-controller-manager.yaml" and backed up old manifest to "/etc/kubernetes/tmp/kubeadm-backup-manifests155856668/kube-controller-manager.yaml"
[upgrade/staticpods] Waiting for the kubelet to restart the component
[apiclient] Found 1 Pods for label selector component=kube-controller-manager
[upgrade/staticpods] Component "kube-controller-manager" upgraded successfully!
[upgrade/staticpods] Moved upgraded manifest to "/etc/kubernetes/manifests/kube-scheduler.yaml" and backed up old manifest to "/etc/kubernetes/tmp/kubeadm-backup-manifests155856668/kube-scheduler.yaml"
[upgrade/staticpods] Waiting for the kubelet to restart the component
[apiclient] Found 1 Pods for label selector component=kube-scheduler
[upgrade/staticpods] Component "kube-scheduler" upgraded successfully!
[uploadconfig] Storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace
[bootstraptoken] Configured RBAC rules to allow Node Bootstrap tokens to post CSRs in order for nodes to get long term certificate credentials
[bootstraptoken] Configured RBAC rules to allow the csrapprover controller automatically approve CSRs from a Node Bootstrap Token
[addons] Applied essential addon: kube-dns
[addons] Applied essential addon: kube-proxy

[upgrade/successful] SUCCESS! Your cluster was upgraded to "v1.8.0". Enjoy!

[upgrade/kubelet] Now that your control plane is upgraded, please proceed with upgrading your kubelets in turn.

kubeadm upgrade apply does the following:

It checks that your cluster is in an upgradeable state, that is:
- The API Server is reachable,
- All nodes are in the Ready state, and
- The control plane is healthy
It enforces the version skew policies.
It makes sure the control plane images are available or available to pull to the machine.
It upgrades the control plane components or rollbacks if any of them fails to come up.
It applies the new kube-dns and kube-proxy manifests and enforces that all necessary RBAC rules are created.

Manually upgrade your Software Defined Network (SDN).

Your Container Network Interface (CNI) provider might have its own upgrade instructions to follow now. Check the addons page to find your CNI provider and see if there are additional upgrade steps necessary.

Add RBAC permissions for automated certificate rotation. In the future, kubeadm will perform this step automatically:

kubectl create clusterrolebinding kubeadm:node-autoapprove-certificate-rotation --clusterrole=system:certificates.k8s.io:certificatesigningrequests:selfnodeclient --group=system:nodes

Upgrading your master and node packages

For each host (referred to as $HOST below) in your cluster, upgrade kubelet by executing the following commands:

Prepare the host for maintenance, marking it unschedulable and evicting the workload:

kubectl drain $HOST --ignore-daemonsets

When running this command against the master host, this error is expected and can be safely ignored (since there are static pods running on the master):

node "master" already cordoned
error: pods not managed by ReplicationController, ReplicaSet, Job, DaemonSet or StatefulSet (use --force to override): etcd-kubeadm, kube-apiserver-kubeadm, kube-controller-manager-kubeadm, kube-scheduler-kubeadm

Upgrade the Kubernetes package versions on the $HOST node by using a Linux distribution-specific package manager:

If the host is running a Debian-based distro such as Ubuntu, run:

apt-get update
apt-get upgrade

If the host is running CentOS or the like, run:

yum update

Now the new version of the kubelet should be running on the host. Verify this using the following command on $HOST:

systemctl status kubelet

Bring the host back online by marking it schedulable:

kubectl uncordon $HOST

After upgrading kubelet on each host in your cluster, verify that all nodes are available again by executing the following (from anywhere, for example, from outside the cluster):

kubectl get nodes

If the STATUS column of the above command shows Ready for all of your hosts, you are done.

Recovering from a bad state

If kubeadm upgrade somehow fails and fails to roll back, due to an unexpected shutdown during execution for instance, you may run kubeadm upgrade again as it is idempotent and should eventually make sure the actual state is the desired state you are declaring.

You can use kubeadm upgrade to change a running cluster with x.x.x --> x.x.x with --force, which can be used to recover from a bad state.

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