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Cheulong Sear
Cheulong Sear

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How to set up k3s on Ubuntu server

#kubernetes #linux #homelab #k3s

What is k3s?

Prerequisite

  1. Servers
  2. Fixed Registration Address
  3. Option: Worker node

Create the control plane

run this script to create a control plane

curl -sfL https://get.k3s.io | sh -
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Create the worker node

To join a worker node to your existing k3s control plane, you need two things from the control-plane node:

  1. The node token
  2. The control-plane node’s IP or hostname

1. Get the node token (on the control-plane node)

Run this on the machine where you installed k3s with your command:

sudo cat /var/lib/rancher/k3s/server/node-token
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Copy this value.

2. Join the worker node

On the worker node, run:

curl -sfL https://get.k3s.io | K3S_URL=https://<CONTROL_PLANE_IP>:6443 K3S_TOKEN=<NODE_TOKEN> sh -
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Example: 

curl -sfL https://get.k3s.io | \
  K3S_URL=https://192.168.1.10:6443 \
  K3S_TOKEN=K10f3a9c7c0f2e7c8d9b3b1a2c3d4e5f6::server:abcdef1234567890 \
  sh -
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Verify the worker joined

Back on the control-plane node:

kubectl get nodes
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You should see something like:

NAME           STATUS   ROLES                  AGE   VERSION
master-1       Ready    control-plane,master   5m    v1.xx.x+k3s
worker-1       Ready    <none>                  1m    v1.xx.x+k3s
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Optional copy kubeconfig to personal pc

On the control-plane node

sudo cp /etc/rancher/k3s/k3s.yaml /tmp/k3s.yaml
sudo chown $USER:$USER /tmp/k3s.yaml
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On your Ubuntu Desktop

scp user@192.0.0.1:/tmp/k3s.yaml ~/.kube/config
chmod 600 ~/.kube/config
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Edit ONLY the server line

nano ~/.kube/config
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change

server: https://127.0.0.1:6443

# to

server: https://<control-plane-ip>:6443
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verification

kubectl config get-contexts
kubectl cluster-info
kubectl get nodes
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Troubleshooting

hostname collusion

On control plane, Run :

sudo systemctl status k3s-agent
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if you see 403 unable to verify password for node ubuntu-server

you might need to change worker-node's hostname
on worker node

# change hostname to worker-1

sudo systemctl stop k3s-agent || true
sudo /usr/local/bin/k3s-agent-uninstall.sh || true
sudo rm -rf /var/lib/rancher/k3s
sudo rm -rf /etc/rancher

sudo hostnamectl set-hostname worker-1
exec bash
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On the CONTROL PLANE — remove the old node entry

kubectl delete node ubuntu-server || true
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Also verify the token:

sudo cat /var/lib/rancher/k3s/server/node-token
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Rejoin the worker with the correct token
On the worker node:

curl -sfL https://get.k3s.io | \
  K3S_URL=https://<CONTROL_PLANE_IP>:6443 \
  K3S_TOKEN=<NODE_TOKEN> \
  sh -

sudo systemctl restart k3s-agent
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=== Done ===

Leave a comment if you have any questions.

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