Step-by-Step Guide to Upgrade a Kubernetes Cluster from v1.17.9 to v1.18.9

Upgrade Overview

Use a kubeadm‑provisioned Kubernetes cluster.

Minor upgrades are supported; major upgrades are allowed but skipping two major versions is not recommended.

Back up all cluster resources before proceeding.

Upgrade Target

Upgrade the cluster from v1.17.9 to v1.18.9 .

<code># kubectl get nodes
NAME            STATUS   ROLES   AGE   VERSION
ecs-968f-0005   Ready    node    102d  v1.17.9
k8s-master      Ready    master  102d  v1.17.9
</code>

Backup the Cluster

kubeadm upgrade

does not affect workloads, but backing up the cluster is recommended. The guide uses the open‑source script k8s-backup-restore :

(1) Download the script

<code>$ mkdir -p /data
cd /data
git clone https://github.com/solomonxu/k8s-backup-restore.git
</code>

(2) Run the backup

<code>cd /data/k8s-backup-restore
./bin/k8s_backup.sh
</code>

To restore:

<code># mkdir -p /data/k8s-backup-restore/data/restore
$ cp devops_deployments_gitlab.yaml ../../restore/
$ cd /data/k8s-backup-restore
./bin/k8s_restore.sh
</code>

Upgrade the Cluster

Master Upgrade

(1) Choose the target version

<code>$ yum list --showduplicates kubeadm --disableexcludes=kubernetes
</code>

(2) Upgrade

kubeadm

to 1.18.9

<code>$ yum install -y kubeadm-1.18.9-0 --disableexcludes=kubernetes
</code>

(3) Verify the version

<code>$ kubeadm version
kubeadm version: &amp;version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.9", ...}
</code>

(4) Drain the master node

<code>$ kubectl cordon k8s-master
$ kubectl drain k8s-master
</code>

(5) Run the upgrade plan

<code>$ kubeadm upgrade plan
</code>

(6) Apply the upgrade

<code>$ kubeadm upgrade apply v1.18.9 --config kubeadm.yaml
</code>

(7) Uncordon the master

<code># kubectl uncordon k8s-master
</code>

Node Upgrade

(1) Upgrade

kubeadm

on the node

<code>$ yum install -y kubeadm-1.18.9-0 --disableexcludes=kubernetes
</code>

(2) Cordon and drain the node

<code>$ kubectl cordon ecs-968f-0005
$ kubectl drain ecs-968f-0005
</code>

(3) Upgrade the node control plane

<code>$ kubeadm upgrade node
</code>

(4) Upgrade

kubelet

and

kubectl

<code>$ yum install -y kubelet-1.18.9-0 kubectl-1.18.9-0 --disableexcludes=kubernetes
$ systemctl daemon-reload
$ systemctl restart kubelet
</code>

(5) Uncordon the node

<code>$ kubectl uncordon ecs-968f-0005
</code>

Verify the Cluster

Check node status

<code>$ kubectl get no
NAME            STATUS   ROLES   AGE   VERSION
ecs-968f-0005   Ready    node    102d  v1.18.9
k8s-master      Ready    master  102d  v1.18.9
</code>

Check certificate expiration

<code>$ kubeadm alpha certs check-expiration
... (output omitted for brevity) ...
</code>

Note: kubeadm upgrade automatically renews certificates it manages on the node. To skip renewal, add the flag --certificate-renewal=false .

Failure Recovery

If an upgrade fails without rollback, you can re‑run

kubeadm upgrade

or force it with

kubeadm upgrade --force

. Backup files are stored under

/etc/kubernetes/tmp

:

kubeadm-backup-etcd-*

– etcd data backup.

kubeadm-backup-manifests-*

– static pod YAML manifests.

Restore etcd data by copying the backup into the etcd data directory, and restore static pod manifests by copying them back to

/etc/kubernetes/manifests

.