Solution

1. Check the current certificate expiration dates

Run the following command from the control plane node.

sudo kubeadm certs check-expiration

This command shows all certificates managed by kubeadm and their expiration dates:

• admin.conf (client certificate for kubectl)
• apiserver (API server serving certificate)
• apiserver-etcd-client (API server to etcd client certificate)
• apiserver-kubelet-client (API server to kubelet client certificate)
• controller-manager.conf (controller manager client certificate)
• etcd-healthcheck-client (etcd health check client certificate)
• etcd-peer (etcd peer certificate for cluster communication)
• etcd-server (etcd server certificate)
• front-proxy-client (front proxy client certificate)
• scheduler.conf (scheduler client certificate)
• super-admin.conf (client certificate bypassing authorization layer)

2. Renew the certificates using kubeadm

You can renew all certificates at once.

sudo kubeadm certs renew all

Or, you can renew specific certificates, for example:

sudo kubeadm certs renew apiserver
sudo kubeadm certs renew apiserver-kubelet-client
sudo kubeadm certs renew controller-manager.conf
sudo kubeadm certs renew scheduler.conf
sudo kubeadm certs renew admin.conf
sudo kubeadm certs renew super-admin.conf

Once, you have renewed the certificates, you can verify the expiration dates have been updated.

sudo kubeadm certs check-expiration

3. Restart the control plane components

First, restart kubelet.

sudo systemctl restart kubelet

Next, move the static Pods manifests temporarily to stop the processes.

sudo mv /etc/kubernetes/manifests/kube-apiserver.yaml /tmp/
sudo mv /etc/kubernetes/manifests/kube-controller-manager.yaml /tmp/
sudo mv /etc/kubernetes/manifests/kube-scheduler.yaml /tmp/
sudo mv /etc/kubernetes/manifests/etcd.yaml /tmp/

Next, wait a couple of seconds to ensure the control plane Pods are terminated

Next, move the manifests back to restart the control plane Pods

sudo mv /tmp/kube-apiserver.yaml /etc/kubernetes/manifests/
sudo mv /tmp/kube-controller-manager.yaml /etc/kubernetes/manifests/
sudo mv /tmp/kube-scheduler.yaml /etc/kubernetes/manifests/
sudo mv /tmp/etcd.yaml /etc/kubernetes/manifests/

Then, wait a few tens of seconds for the Pods to restart.

4. Verify the cluster is working correctly

First, update your local kubeconfig with the renewed admin certificate

sudo cp /etc/kubernetes/admin.conf ~/.kube/config
sudo chown $(id -u):$(id -g) ~/.kube/config

Next, check the cluster’s status.

kubectl cluster-info

You can also verify the Nodes are ready, and run a couple of basic commands.

kubectl get nodes
kubectl get pods -n kube-system
kubectl get namespaces