Add worker node to Kubernetes Cluster

In this tutorial, we will learn about how to add worker node to an existing Kubernetes Cluster. To learn more about how to create a single node Kubernetes cluster, please refer to section Create single node Kubernetes cluster on Ubuntu using kubeadm on Google Cloud Platform (GCP). Same steps which are mentioned below could be also performed on any Kubernetes cluster created on Ubuntu whether they are hosted on Google Cloud Platform (GCP) or not.

Get discovery token

In case you want to initializes a Kubernetes worker node and join it to an existing Kubernetes cluster, you can use kubeadm join command like below:

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kubeadm join 10.240.0.10:6443 --token qime8q.8mpf97fdxxxxxxxx \
    --discovery-token-ca-cert-hash sha256:8f61ee1955f194f6cc7a6888baf37447b29a86a93b214205154a8abdxxxxxxxx

When you configure a fresh Kubernetes cluster using kubeadm init, you will get the token information as part of the output itself.

kubeadm init creates an initial token with a 24-hour TTL. So in case you need to generate new token to join worker node, use below command:

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kubeadm token create --print-join-command

As we have given --print-join-command option, instead of printing only the token, it prints the full kubeadm join flag needed to join the cluster using the token.

Run kubeadm join

Once you have a valid token, you can run the kubeadm join command.

Sample output:

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$ sudo kubeadm join 10.240.0.10:6443 --token qime8q.8mpf97fdxxxxxxxx \
    --discovery-token-ca-cert-hash sha256:8f61ee1955f194f6cc7a6888baf37447b29a86a93b214205154a8abdxxxxxxxx
W0529 07:12:00.016796    4465 join.go:346] [preflight] WARNING: JoinControlPane.controlPlane settings will be ignored when control-plane flag is not set.
[preflight] Running pre-flight checks
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'
[kubelet-start] Downloading configuration for the kubelet from the "kubelet-config-1.18" ConfigMap in the kube-system namespace
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Starting the kubelet
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...
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.