Installation nodejs using K3s in High Availability (HA) Mode with MetalLB

1. Prepare the Environment

• Prerequisites:
  • Multiple Linux nodes (virtual or bare metal) with unique hostnames.
  • Shared network segment with 2–3 free IPs for MetalLB.
  • SSH access to all nodes.

2. Install K3s in High Availability (HA) Mode

K3s offers two HA modes: with external DB (etcd, MySQL, PostgreSQL) or embedded etcd. Here is a simplified approach using embedded etcd:

a. On the first server node, initialize the cluster:

# Set a strong secret token

SECRET=CHANGE_ME_SECRET_TOKEN

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

--token=${SECRET} \

--cluster-init \

--disable traefik \

--disable servicelb \ --write-kubeconfig-mode=644

• --disable traefik disables the default ingress; you can use your own.
• --disable servicelb disables the default load balancer in K3s (Klipper), required to use MetalLB instead.

b. On additional server nodes, join the cluster:

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

--token=${SECRET} \

--server https://:6443 \

--disable traefik \

--disable servicelb \

--write-kubeconfig-mode=644

c. On agent (worker) nodes, join:

Get the node token from one server node:

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

On the worker node:

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

Verify with:

kubectl get nodes

3. Install MetalLB for Load Balancing

a. Install MetalLB (manifest method): 

kubectl apply -f https://raw.githubusercontent.com/metallb/metallb/v0.13.7/config/manifests/metallb-native.yaml

Or via Helm:

helm repo add metallb https://metallb.github.io/metallb

helm install metallb metallb/metallb --namespace metallb-system --create-namespace

b. Set up an IP Address Pool for MetalLB

Create a metallb-config.yaml file:

apiVersion: metallb.io/v1beta1 kind: IPAddressPool

metadata:

  name: default

  namespace: metallb-system

spec:

  addresses:

  - 192.168.1.240-192.168.1.250 # Adjust to match your network!

---

apiVersion: metallb.io/v1beta1

kind: L2Advertisement metadata:

  name: default

  namespace: metallb-system

Then apply it:

kubectl apply -f metallb-config.yaml

This allocates a set of external IPs for MetalLB to hand out to LoadBalancer type services.

4. Install Node.js in Pods on K3s

You typically do not install Node.js directly on the cluster nodes, but inside containers.

For example, you can create a Deployment using the official Node.js container image:

node-deployment.yaml:

apiVersion: apps/v1

kind: Deployment

metadata:

  name: nodejs-app

spec:

  replicas: 3

  selector:

    matchLabels:

      app: nodejs-app

  template:

    metadata:

      labels:

        app: nodejs-app

    spec:

      containers:

      - name: nodejs

        image: node:18 # Or another version you need

        ports:

        - containerPort: 3000 command: ["node", "YOUR_APP.js"] # replace with your script

Apply:

kubectl apply -f node-deployment.yaml

5. Expose Node.js with LoadBalancer Service

Create a nodejs-service.yaml:

apiVersion: v1

kind: Service

metadata:

  name: nodejs-service

spec:

  selector:

    app: nodejs-app

  ports:

  - protocol: TCP

    port: 80

    targetPort: 3000

  type: LoadBalancer

Apply:

kubectl apply -f nodejs-service.yaml

After a few moments, kubectl get svc will show an EXTERNAL-IP assigned from MetalLB's pool. This service distributes incoming requests to all Node.js pods, providing both load balancing and high availability.

In Summary:

Deploy K3s with HA mode and disable built-in load balancer (servicelb).

Install MetalLB and configure your external IP pool.

Deploy Node.js apps as Kubernetes Deployments.

Use LoadBalancer-type Services to expose your apps via MetalLB, providing external traffic balancing and failover.

This approach gives you both cluster control-plane and application-level high availability.