Adding Linux worker nodes

This page explains how to add Linux worker nodes to a kubeadm cluster.

Before you begin

• Each joining worker node has installed the required components from Installing kubeadm, such as, kubeadm, the kubelet and a container runtime.
• A running kubeadm cluster created by kubeadm init and following the steps in the document Creating a cluster with kubeadm.
• You need superuser access to the node.

Adding Linux worker nodes

To add new Linux worker nodes to your cluster do the following for each machine:

1. Connect to the machine by using SSH or another method.
2. Run the command that was output by kubeadm init. For example:

sudo kubeadm join --token <token> <control-plane-host>:<control-plane-port> --discovery-token-ca-cert-hash sha256:<hash>

Additional information for kubeadm join

If you do not have the token, you can get it by running the following command on the control plane node:

# Run this on a control plane node
sudo kubeadm token list

The output is similar to this:

TOKEN                    TTL  EXPIRES              USAGES           DESCRIPTION            EXTRA GROUPS
8ewj1p.9r9hcjoqgajrj4gi  23h  2018-06-12T02:51:28Z authentication,  The default bootstrap  system:
                                                   signing          token generated by     bootstrappers:
                                                                    'kubeadm init'.        kubeadm:
                                                                                           default-node-token

By default, node join tokens expire after 24 hours. If you are joining a node to the cluster after the current token has expired, you can create a new token by running the following command on the control plane node:

# Run this on a control plane node
sudo kubeadm token create

The output is similar to this:

5didvk.d09sbcov8ph2amjw

If you don't have the value of --discovery-token-ca-cert-hash, you can get it by running the following commands on the control plane node:

# Run this on a control plane node
sudo cat /etc/kubernetes/pki/ca.crt | openssl x509 -pubkey  | openssl rsa -pubin -outform der 2>/dev/null | \
   openssl dgst -sha256 -hex | sed 's/^.* //'

The output is similar to:

8cb2de97839780a412b93877f8507ad6c94f73add17d5d7058e91741c9d5ec78

The output of the kubeadm join command should look something like:

[preflight] Running pre-flight checks

... (log output of join workflow) ...

Node join complete:
* Certificate signing request sent to control-plane and response
  received.
* Kubelet informed of new secure connection details.

Run 'kubectl get nodes' on control-plane to see this machine join.

A few seconds later, you should notice this node in the output from kubectl get nodes. (for example, run kubectl on a control plane node).

What's next

• See how to add Windows worker nodes.