K3s Lightweight Kubernetes Instalaation

K3s es un ligero, fully certified Kubernetes distribution designed for resource-constrained environments, IoT devices, edge computing, and development. Esta guía cubre single-node and multi-node K3s installation, agent configuration, built-in features like Traefik and local-path almacenamiento, and implementación considerations for your VPS and baremetal infrastructure.

Tabla de contenidos

• K3s Overview
• Single-Node Instalaation
• Multi-Node Instalaation
• Built-in Components
• Configuration and Customization
• Troubleshooting
• Practical Examples
• Conclusion

K3s Overview

What is K3s?

K3s es un ligero Kubernetes distribution that:

• Runs in < 512MB RAM
• Only requires 200MB disk space (base binary)
• Fully certified Kubernetes conformance
• Single binary installation
• Includes batteries (Traefik, local-path almacenamiento)

K3s vs Full Kubernetes

Arquitectura

Server (Control Plane): kube-apiserver, etcd, scheduler, controller-manager
Agent (Worker): kubelet, kube-proxy
Built-in: Traefik ingress, local-path storage, CoreDNS

Single-Node Instalaation

Requisitos previos

• Linux kernel v3.10+
• 512MB+ RAM
• 200MB+ disk space
• Internet connectivity

Quick Instalaation

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

This installs K3s server with defaults.

Wait for ready:

kubectl get nodes
kubectl get pods -A

Verifica Instalaation

# Check k3s service
sudo systemctl status k3s

# Test cluster
kubectl cluster-info
kubectl get nodes
kubectl get pods -A

Configura kubectl Access

K3s automatically creates kubeconfig:

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

# Or as regular user
mkdir -p ~/.kube
sudo cp /etc/rancher/k3s/k3s.yaml ~/.kube/config
sudo chown $USER:$USER ~/.kube/config
chmod 600 ~/.kube/config

Multi-Node Instalaation

Server Instalaation

On first server node:

# Install K3s server
curl -sfL https://get.k3s.io | sh -

# Get server token
cat /var/lib/rancher/k3s/server/node-token

Agent Instalaation

On worker nodes:

# Export server token and IP
export K3S_URL=https://server-ip:6443
export K3S_TOKEN=server-token-from-above

# Install K3s agent
curl -sfL https://get.k3s.io | sh -

Or with explicit parameters:

curl -sfL https://get.k3s.io | K3S_URL=https://server-ip:6443 K3S_TOKEN=token sh -

Verifica Multi-Node Cluster

# On server, view all nodes
kubectl get nodes

# Expected output: server and agents showing Ready

Alta disponibilidad K3s

For production, use external database instead of embedded etcd:

# On server with external database
curl -sfL https://get.k3s.io | \
  K3S_DATASTORE_ENDPOINT=postgres://user:pass@db-ip:5432/k3s \
  K3S_DATASTORE_CAFILE=/path/to/ca.crt \
  K3S_DATASTORE_CERTFILE=/path/to/cert.crt \
  K3S_DATASTORE_KEYFILE=/path/to/key.key \
  sh -

Supported databases:

• PostgreSQL
• MySQL
• etcd (external)

Built-in Components

Traefik Ingress Controller

K3s includes Traefik by default. Deploy ingreso:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: myapp
  namespace: default
spec:
  ingressClassName: traefik
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: myapp
            port:
              number: 80

Access Traefik dashboard:

kubectl port-forward -n kube-system svc/traefik 9000:9000
# Visit http://localhost:9000/dashboard/

Disable Traefik:

curl -sfL https://get.k3s.io | INSTALL_K3S_EXEC="--disable traefik" sh -

Local-Path Storage

K3s includes local-path-provisioner for persistente almacenamiento:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-data
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: local-path
  resources:
    requests:
      storage: 10Gi
---
apiVersion: v1
kind: Pod
metadata:
  name: test
spec:
  containers:
  - name: test
    image: busybox
    volumeMounts:
    - name: data
      mountPath: /data
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: my-data

CoreDNS

DNS is included and configured by default.

Check DNS:

kubectl get pods -n kube-system | grep coredns

Configuración and Customization

Server Configuration

curl -sfL https://get.k3s.io | sh -s - \
  --disable traefik \
  --disable servicelb \
  --disable metrics-server \
  --docker \
  --kubelet-arg "max-pods=200" \
  --kube-apiserver-arg "feature-gates=EphemeralContainers=true" \
  --data-dir /var/lib/rancher/k3s

Configuración File

Create K3s configuration:

# /etc/rancher/k3s/config.yaml
server: https://server-ip:6443
token: server-token
resolveConf: /etc/resolv.conf
disable:
  - traefik
disable-helm-self-chart: false
node-label:
  - "environment=production"

Start with config file:

K3S_CONFIG_FILE=/etc/rancher/k3s/config.yaml curl -sfL https://get.k3s.io | sh -

Custom Manifests

Place manifests in /var/lib/rancher/k3s/server/manifests/:

# Create custom deployment
cat > /var/lib/rancher/k3s/server/manifests/custom-app.yaml << 'EOF'
apiVersion: apps/v1
kind: Deployment
metadata:
  name: custom-app
spec:
  replicas: 1
  selector:
    matchLabels:
      app: custom-app
  template:
    metadata:
      labels:
        app: custom-app
    spec:
      containers:
      - name: app
        image: myapp:1.0
EOF

# K3s will automatically apply on startup

Solución de problemas

Service Won't Start

# Check service status
sudo systemctl status k3s

# View logs
sudo journalctl -u k3s -n 100

# Check if port 6443 is already in use
sudo netstat -tlnp | grep 6443

Node Join Issues

# Verify token is correct
cat /var/lib/rancher/k3s/server/node-token

# Check agent logs
sudo journalctl -u k3s-agent -n 100

# Verify connectivity to server
ping server-ip
curl https://server-ip:6443/ping

Storage Issues

# Check local-path provisioner
kubectl get pods -n local-path-storage

# View PVC status
kubectl get pvc
kubectl describe pvc my-data

# Check node storage
df -h /var/lib/rancher/k3s

Practical Examples

Ejemplo: Single-Node K3s Setup

#!/bin/bash

echo "=== Installing K3s Server ==="
curl -sfL https://get.k3s.io | sh -

echo "=== Waiting for K3s to be ready ==="
sleep 10

echo "=== Setting up kubeconfig ==="
mkdir -p ~/.kube
sudo cp /etc/rancher/k3s/k3s.yaml ~/.kube/config
sudo chown $USER:$USER ~/.kube/config

echo "=== Verifying cluster ==="
kubectl cluster-info
kubectl get nodes
kubectl get pods -A

echo "=== K3s installed successfully ==="
echo "Deploy apps with: kubectl apply -f manifest.yaml"

Ejemplo: Multi-Node K3s Cluster

#!/bin/bash

# Setup server node
echo "=== Installing K3s Server ==="
SERVER_IP="192.168.1.100"
curl -sfL https://get.k3s.io | sh -
TOKEN=$(cat /var/lib/rancher/k3s/server/node-token)

echo "Server token: $TOKEN"
echo "Server IP: $SERVER_IP"

# Setup agent nodes
AGENTS=("192.168.1.101" "192.168.1.102" "192.168.1.103")

for agent_ip in "${AGENTS[@]}"; do
  echo "=== Installing agent on $agent_ip ==="
  ssh root@$agent_ip << EOF
curl -sfL https://get.k3s.io | K3S_URL=https://$SERVER_IP:6443 K3S_TOKEN=$TOKEN sh -
EOF
done

# Verify cluster
kubectl get nodes

Ejemplo: K3s with Custom Configuration

#!/bin/bash

# Install K3s with custom settings
curl -sfL https://get.k3s.io | sh -s - \
  --cluster-init \
  --disable traefik \
  --disable servicelb \
  --kubelet-arg "max-pods=250" \
  --kubelet-arg "eviction-hard=memory.available<100Mi" \
  --kube-apiserver-arg "feature-gates=EphemeralContainers=true" \
  --node-label "node-role=master" \
  --node-taint "master=true:NoSchedule"

# Deploy custom ingress
kubectl apply -f - << 'EOF'
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: example
  annotations:
    cert-manager.io/cluster-issuer: letsencrypt
spec:
  tls:
  - hosts:
    - example.com
    secretName: example-tls
  rules:
  - host: example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: example
            port:
              number: 80
EOF

Conclusión

K3s is an excellent choice for Kubernetes implementacións on resource-constrained VPS and baremetal servers. Its lightweight nature, quick installation, and built-in components make it ideal for development, edge computing, and small production implementacións. Start with a single-node K3s clúster for development, expand to multi-node for production workloads, and leverage the built-in Traefik and local-path almacenamiento for immediate functionality. K3s provides the full Kubernetes experience in a minimal package, making it perfect for teams looking to adopt Kubernetes without the operational overhead of full distributions.