After Ubuntu 20.04 LTS is successfully added to the cluster on the node, the following prompt will appear:

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.

Verify the success of adding by kubectl get nodes command. The following error occurs:

The connection to the server localhost:8080 was refused - did you specify the right host or port?

This error has also occurred on the master node. The solution gives the answer after successful installation

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

Alternatively, if you are the root user, you can run:

  export KUBECONFIG=/etc/kubernetes/admin.conf

I use the root account, so I need to execute the following command:

export KUBECONFIG=/etc/kubernetes/admin.conf

After the command is executed, verify it:

root@k8s-master-03:/etc/kubernetes# kubectl get nodes
W0706 10:27:55.181115   22817 loader.go:221] Config not found: /etc/kubernetes/admin.conf
The connection to the server localhost:8080 was refused - did you specify the right host or port?

The key information of the error report is that the configuration is not found

Config not found: /etc/kubernetes/admin.conf

Let’s go to the /etc/kubernetes/ Directory:

root@k8s-master-03:/etc/kubernetes# ls -l
total 12
-rw------- 1 root root 1910 Jul  6 09:52 kubelet.conf
drwxr-xr-x 2 root root 4096 Jul  6 09:41 manifests
drwxr-xr-x 2 root root 4096 Jul  6 09:52 pki

The results show that only kubelet. Conf (master node has admin. CONF), so we need to execute the following command:

export KUBECONFIG=/etc/kubernetes/kubelet.conf