Introduction:

In this guide, we’ll set up a lightweight Kubernetes cluster using K3s on CentOS 7. K3s is a fast and easy way to run Kubernetes without heavy resource usage. With one master and multiple worker nodes, you can build a clean, efficient, and production-ready cluster in just a few steps.

Lab Details

  • VM1: k8s-master — <public-ip>
  • VM2: worker-node1 — <public-ip>
  • VM3: worker-node2 — <public-ip>
  • VM4: worker-node3 — <public-ip>

1. Set Hostname on Each Node

Set the hostname on every server.

Master Node:

sudo hostnamectl set-hostname k8s-master && exec bash

Worker Nodes:

$sudo hostnamectl set-hostname worker-node1 && exec bash
$sudo hostnamectl set-hostname worker-node2 && exec bash
$sudo hostnamectl set-hostname worker-node3 && exec bash

Update /etc/hosts on all nodes

Add the public IPs and hostnames of all nodes:

<public-ip>  k8s-master
<public-ip>  worker-node1
<public-ip>  worker-node2
<public-ip>  worker-node3

2. Install Required Tools

Install basic utilities on all nodes:

$sudo yum install curl wget -y

3. Install K3s on Master Node:

Run the following command only on the master:

$curl -sfL https://get.k3s.io | sh -

Check whether K3s is running:

$sudo systemctl status k3s

4. Configure kubectl on Master Node

$mkdir ~/.kube
$sudo cp /etc/rancher/k3s/k3s.yaml ~/.kube/config
$sudo chown $USER ~/.kube/config
$sudo chmod 600 ~/.kube/config
$export KUBECONFIG=~/.kube/config

Verify the cluster:

$kubectl get nodes

You should see the master node in Ready state.

5. Join Worker Nodes to the Cluster

Get the K3s token from master:

$sudo cat /var/lib/rancher/k3s/server/node-token

Copy the token.

Run on all worker nodes:

$curl -sfL https://get.k3s.io | K3S_URL=https://k8s-master:6443 K3S_TOKEN=<TOKEN> sh -

(Replace <TOKEN> with the actual key.)

Add master host entry (on workers):

<Master-IP>  k8s-master

Verify from master:

kubectl get nodes

All nodes should appear in Ready status.

6. Final Verification:

Run the following commands:

$kubectl get pods -A
$kubectl get nodes
$kubectl cluster-info

Output:

If all components (CoreDNS, metrics-server, node agents) are running, your K3s Kubernetes cluster is successfully set up.

Conclusion:

With just a few simple steps, K3s lets you build a clean, lightweight, and fully functional Kubernetes cluster on CentOS 7. It’s fast to install, easy to manage, and perfect for development, testing, and small production setups.

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