Upgrade A Cluster

This page provides an overview of the steps you should follow to upgrade a Kubernetes cluster.

The way that you upgrade a cluster depends on how you initially deployed it and on any subsequent changes.

At a high level, the steps you perform are:

• Upgrade the control plane
• Upgrade the nodes in your cluster
• Upgrade clients such as kubectl
• Adjust manifests and other resources based on the API changes that accompany the new Kubernetes version

Before you begin

You must have an existing cluster. This page is about upgrading from Kubernetes 1.20 to Kubernetes 1.21. If your cluster is not currently running Kubernetes 1.20 then please check the documentation for the version of Kubernetes that you plan to upgrade to.

Upgrade approaches

kubeadm

If your cluster was deployed using the kubeadm tool, refer to Upgrading kubeadm clusters for detailed information on how to upgrade the cluster.

Once you have upgraded the cluster, remember to install the latest version of kubectl.

Manual deployments

Caution: These steps do not account for third-party extensions such as network and storage plugins.

You should manually update the control plane following this sequence:

• etcd (all instances)
• kube-apiserver (all control plane hosts)
• kube-controller-manager
• kube-scheduler
• cloud controller manager, if you use one

At this point you should install the latest version of kubectl.

For each node in your cluster, drain that node and then either replace it with a new node that uses the 1.21 kubelet, or upgrade the kubelet on that node and bring the node back into service.

Other deployments

Refer to the documentation for your cluster deployment tool to learn the recommended set up steps for maintenance.

Post-upgrade tasks

Switch your cluster's storage API version

The objects that are serialized into etcd for a cluster's internal representation of the Kubernetes resources active in the cluster are written using a particular version of the API.

When the supported API changes, these objects may need to be rewritten in the newer API. Failure to do this will eventually result in resources that are no longer decodable or usable by the Kubernetes API server.

For each affected object, fetch it using the latest supported API and then write it back also using the latest supported API.

Update manifests

Upgrading to a new Kubernetes version can provide new APIs.

You can use kubectl convert command to convert manifests between different API versions. For example:

kubectl convert -f pod.yaml --output-version v1

The kubectl tool replaces the contents of pod.yaml with a manifest that sets kind to Pod (unchanged), but with a revised apiVersion.