Upgrading a Kubernetes Cluster using kubeadm

In this article, we will look how we can upgrade a Kubernetes cluster using kubeadm

Prerequisites

• We need a working Kubernetes cluster created using kubeadm
• If you haven’t createdmthe cluster, please check my previous article below
  This will guide you to create a Kubernetes v1.27.0 cluster

Building a Kubernetes Cluster using kubeadm

Steps

Control Plane

• Verify the version of our cluster by executing the below command in the [control-plane] instance

$ kubectl get nodes
NAME            STATUS   ROLES           AGE    VERSION
control-plane   Ready    control-plane   7m5s   v1.27.0
node-1          Ready    <none>          91s    v1.27.0
node-2          Ready    <none>          17s    v1.27.0

• Update the package index and find the latest kubeadm patch available in the repository

$ sudo apt update

$ sudo apt-cache madison kubeadm

• Unhold the kubeadm package for upgrading

$ sudo apt-cache unhold kubeadm

• Upgrade the kubeadm package to version v1.27.1 and hold the package from automatic upgrading

$ sudo apt install -y kubeadm=1.27.1-00

$ sudo apt-mark hold kubeadm

• Check the upgraded kubeadm version and verify the upgrade plan

$ sudo kubeadm version

$ sudo kubeadm upgrade plan

• Once our plan is verified, we can upgrade the [control-plane] by executing the below command

$ sudo kubeadm upgrade apply v1.27.1

• Prepare the [control-plane] node for maintenance by marking it unschedulable and evicting the workloads

$ kubectl drain control-plane --ignore-daemonsets

• Unhold the kubelet and kubectl packages for upgrade

$ sudo apt-mark unhold kubelet kubectl

• Upgrade kubelet and kubectl packages to version v1.27.1 and hold the packages from automatic upgrading

$ sudo apt install kubelet=1.27.1-00 kubectl=1.27.1-00

$ sudo apt-mark hold kubelet kubectl

• Restart the kubelet on [control-plane]

$ sudo systemctl daemon-reload

$ sudo systemctl restart kubelet

• Uncordon the [control-plane] for marking it as schedulable

$ kubectl uncordon control-plane

• Verify the nodes, now we can see [control-plane] is upgraded to v1.27.1

$ kubectl get nodes
NAME            STATUS   ROLES           AGE    VERSION
control-plane   Ready    control-plane   118m   v1.27.1
node-1          Ready    <none>          112m   v1.27.0
node-2          Ready    <none>          111m   v1.27.0

Nodes

• Update the package index on [node-1] and unhold the kubeadm package for upgrading

$ sudo apt update

$ sudo apt-mark unhold kubeadm

• Upgrade the kubeadm package to version v1.27.1 on [node-1] and hold the package from automatic upgrading

$ sudo apt install kubeadm=1.27.1-00

$ sudo apt-mark hold kubeadm

• Upgrade the cluster configuration on [node-1] using the below command

$ sudo kubeadm upgrade node

• Prepare the [node-1] for maintenance by marking it unschedulable and evicting the workloads
  Execute the below drain command on [control-plane]

$ kubectl drain node-1 --ignore-daemonsets --force

• Unhold the kubelet and kubectl packages for upgrade

$ sudo apt-mark unhold kubelet kubectl

• Upgrade kubelet and kubectl packages to version v1.27.1 and hold the packages from automatic upgrading

$ sudo apt install kubelet=1.27.1-00 kubectl=1.27.1-00

$ sudo apt-mark hold kubelet kubectl

• Restart the kubelet on [node-1]

$ sudo systemctl daemon-reload

$ sudo systemctl restart kubelet

• Uncordon the [node-1] for marking it as schedulable
  Execute the below uncordon command on [control-plane]

$ kubectl uncordon node-1

• Repeat the above steps for [node-2] also
• Now our cluster is fully upgraded to v1.27.1
  Verify the same by executing the below command on [control-plane]

$ kubectl get nodes
NAME            STATUS   ROLES           AGE    VERSION
control-plane   Ready    control-plane   136m   v1.27.1
node-1          Ready    <none>          131m   v1.27.1
node-2          Ready    <none>          129m   v1.27.1

Reference

https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/kubeadm-upgrade/

https://kubernetes.io/docs/tasks/administer-cluster/kubeadm/upgrading-linux-nodes/