...

To remove administrator privileges, simply follow the simple steps in the previous output. Repeat the same commands as root if you also want to use the cluster in administrator mode.

As  As for the second point in the list, there are multiple CNI (Container Network Interfaces) to generate our Pod network. Here we use Calico (official guide), but obviously there are valid alternatives listed at the address shown in the command above (we report the link here). So let's run the command (check the version)

$ kubectl apply -f https://docs.projectcalico.org/v3.17/manifests/calico.yaml
# Flannel is an alternative
$ kubectl apply -f https://raw.githubusercontent.com/flannel-io/flannel/master/Documentation/kube-flannel.yml

Now let's finally expand our cluster by adding worker nodes. Let's connect to the nodes via SSH and take administrator privileges. Now we paste the command, saved previously, returned to us by kubeadm init

...

$ kubectl get nodes
NAME                   STATUS   ROLES    AGE   VERSION
mycentos-0.novalocal   Ready    master   30h   v1.2021.01
mycentos-1.novalocal   Ready    <none>   25h   v1.2021.01
mycentos-2.novalocal   Ready    <none>   24h   v1.2021.01

The output should list the nodes that are part of the cluster.

Upgrading kubeadm clusters

To update the cluster, follow cluster follow the instructions in the official guide, that explains how to upgrade a Kubernetes cluster created with kubeadm. The upgrade workflow at high level is the following:

...