After the installation phase, we can set up our cluster (official guide). To do this, simply run as root the following command on the control-plane
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# For the moment launch the command without arguments The following command accepts several arguments, but for building a small test cluster let's run it without them $ kubeadm init <args> . . . # At the end of the procedure, an output similar to this will appear Your Kubernetes control-plane has initialized successfully! To start using your cluster, you need to run the following as a regular user: mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config You should now deploy a Pod network to the cluster. Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at: /docs/concepts/cluster-administration/addons/ You can now join any number of machines by running the following on each node as root: kubeadm join <control-plane-host>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash sha256:<hash> |
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We are now building a simple cluster, consisting of a control-plane with n workers, so we run the |
The output shown above gives us 3 information:
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To remove administrator privileges, simply follow the simple steps in the previous output. Repeat the same commands as root if you also want to use the cluster in administrator mode.
As . As for the second point in the list, there are multiple CNI (Container Network Interfaces) to generate our Pod network. Here we use Calico (official guide here), but obviously there are valid alternatives listed at the address shown in the command above (we report the link here). So let's run the command (check the version)
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$ 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
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$ kubeadm join <control-plane-host>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash sha256:<hash>
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This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.
Run 'kubectl get nodes' on the control-plane to see this node join the cluster. |
To retrieve the token later, type the command
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$ kubectl get nodes NAME STATUS ROLES AGE VERSION mycentos-0.novalocal Ready master 30h v1.1921.21 mycentos-1.novalocal Ready <none> 25h v1.1921.21 mycentos-2.novalocal Ready <none> 24h v1.1921.21 |
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:
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