How do I find the join command for kubeadm on the master?

To print a join command for a new worker node use:

• kubeadm token create --print-join-command

But if you need to join a new control plane node, you need to recreate a new key for the control plane join command. This can be done with three simple steps:

1. Re upload certificates in the already working master node with kubeadm init phase upload-certs --upload-certs. That will generate a new certificate key.

2. Print join command in the already working master node with kubeadm token create --print-join-command.

3. Join a new control plane node with $JOIN_COMMAND_FROM_STEP2 --control-plane --certificate-key $KEY_FROM_STEP1.

This might not work for the old Kubernetes versions but I tried with the new version and it worked for me.

kubeadm token create --print-join-command