Shelner

Posted on Jan 3

K3s server setup guide using Ubuntu22

#k3s #kubernetes #ubuntu

I explain what each command does and focusing on k3s and Kubernetes concepts.

Set up Ubuntu

Login using SSH
Update & Install tools: sudo apt update && sudo apt install -y curl vim git

Disable Swap (Required for Kubernetes)

sudo swapoff -a

swap: Disk space used as virtual memory.
Why disable swap? Kubernetes requires swap to be disabled because it expects full control over memory management.

sudo sed -i '/ swap / s/^/#/' /etc/fstab

/etc/fstab: File that defines filesystems mounted at boot.
sed -i: Edits the file in place.
This command comments out swap entries, so swap stays disabled after reboot.

Install K3s

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

curl -sfL:
- -s: silent
- -f: fail on error
- -L: follow redirects
https://get.k3s.io: Official k3s installation script.
| sh -: Pipes the script directly into the shell and executes it.

This installs:

K3s server
containerd
kubectl (boundled)

Check K3s Service

sudo systemctl status k3s

status k3s: Confirms that the k3s server is running correctly.

Set kubeconfig

export KUBECONFIG=/etc/rancher/k3s/k3s.yaml

KUBECONFIG: File that tells kubectl how to connect to the cluster.
/etc/rancher/k3s/k3s.yaml: Default kubeconfig generated by k3s.

※Without this, kubectl may not work for non-root users.

Verify Cluster

sudo kubectl get nodes

kubectl: Kubernetes command-line tool.
get nodes: Shows all nodes in the cluster.
Output confirms:
- k3s is running
- this VM is acting as a control-plane + worker node

Create Nginx Pod

vim ~/nginx-pod.yaml

Pod Yaml

apiVersion: v1
kind: Pod
metadata:
  name: hi-nginx
spec:
  containers:
  - name: nginx
    image: nginx:stable-alpine
    ports:
    - containerPort: 80

Explanation

apiVersion: v1: Core Kubernetes API.
kind: Pod: Smallest deployable unit in Kubernetes.
metadata.name: Pod name.
spec.containers: List of containers inside the pod
image: nginx:stable-alpine: Lightweight Nginx image
containerPort: 80: Port exposed inside the container.

Create Pod

sudo kubectl apply -f ~/nginx-pod.yaml

apply: Creates or updates resources declaratively.
-f: Uses the YAML file.

Check Pods

sudo kubectl get pods

Shows pod status (Running, Pending, etc.).

Organaize Files

mkdir ~/k3s-pod
mv ~/nginx-pod.yaml ~/k3s-pod/
cd ~/k3s-pod/

Creates a directory to organize Kubernetes manifests.

Create Service (NodePort)

vim ~/k3s-pod/nginx-service.yaml

Service YAML

apiVersion: v1
kind: Service
metadata:
  name: nginx-svc
spec:
  type: NodePort
  selector:
    app: nginx
  ports:
  - port: 80
    targetPort: 80
    nodePort: 30090

Explanation:

kind: Service: Exposes pods to the network.
type: NodePort: Opens a port on every node's IP.
selector: Finds pods with label app=nginx.
port: Service port.
targetPort: Container port.
nodePort: 30090: External port accessible via NodeIP:30090.

Add Label to Pod

sudo kubectl label pod hi-nginx app=nginx

Labels are key-vakye pairs used by Services and Deployments.
Required so the Service can find the Pod.

Create Service

sudo kubectl apply -f ~/k3s-pod/nginx-service.yaml

Find IP Address

ip a

Shows network interfaces.
eth0 usually holds the node IP.

Private IP Ranges

10.0.0.0 - 10.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

These are private IP addresses.
Not reachable directly from the internet.

Access Nginx

curl http://10.140.11.1:30090

Access Nginx via:
- Node.IP
- NodePort

You can laso use:

curl http://<HOST_NAME>:30090
curl http://<Global_IP>:30090

Create Deployment

vim ~/k3s-pod/nginx-deploy.yaml

Deployment YAML

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deploy
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:stable-alpine
        ports:
        - containerPort: 80