Deploying JavaScript (Node.js) on Kubernetes: A Step-by-Step Guide

Introduction: Why Kubernetes for Node.js?

Modern JavaScript (Node.js) web applications require high availability, scalability, and fault tolerance. When your application grows beyond a single server, manual management becomes a nightmare. This is where Kubernetes (K8s) comes to the rescue — a container orchestration system that automates deployment, scaling, and management of applications.

In this guide, we will go through the complete journey: from a simple Node.js application to running it in a production-like environment on Kubernetes. You will learn how to package your code into a Docker image, create the necessary K8s resources (Pod, Deployment, Service), and configure external access.

1. Preparing the Node.js Application

First, let's create a simple Express application. It will respond to HTTP requests and display the container hostname (useful for checking load balancing).

1.1. File app.js

const express = require('express');const os = require('os');

const app = express();const PORT = process.env.PORT || 3000;

app.get('/', (req, res) => {  res.json({    message: 'Hello from Node.js on Kubernetes!',    hostname: os.hostname(),    timestamp: new Date().toISOString()  });});

app.listen(PORT, () => {  console.log(`Server running on port ${PORT}`);});

1.2. File package.json

{  "name": "k8s-node-app",  "version": "1.0.0",  "dependencies": {    "express": "^4.18.2"  },  "scripts": {    "start": "node app.js"  }}

2. Containerization: Docker Image

Kubernetes works with containers. Let's create a minimal Dockerfile for our Node.js application. We'll use the official Node.js image and multi-stage build to optimize size.

2.1. Dockerfile

FROM node:18-alpine AS builderWORKDIR /appCOPY package*.json ./RUN npm ci --only=production

FROM node:18-alpineWORKDIR /appCOPY --from=builder /app/node_modules ./node_modulesCOPY . .EXPOSE 3000CMD ["node", "app.js"]

Build the image and push it to Docker Hub or another registry:

docker build -t your-dockerhub/k8s-node-app:v1 .docker push your-dockerhub/k8s-node-app:v1

3. Deploying to Kubernetes

Now let's move to the main part — creating Kubernetes resources. We will use Deployment (to manage Pods) and Service (for network access).

3.1. Creating a Deployment

A Deployment ensures that the desired number of Pods with your application are always running. Create a file deployment.yaml:

apiVersion: apps/v1kind: Deploymentmetadata:  name: node-app-deployment  labels:    app: node-appspec:  replicas: 3  selector:    matchLabels:      app: node-app  template:    metadata:      labels:        app: node-app    spec:      containers:      - name: node-app        image: your-dockerhub/k8s-node-app:v1        ports:        - containerPort: 3000        env:        - name: PORT          value: "3000"        resources:          requests:            memory: "64Mi"            cpu: "100m"          limits:            memory: "128Mi"            cpu: "200m"

3.2. Creating a Service

A Service provides a stable IP address and DNS name for accessing Pods. Create service.yaml:

apiVersion: v1kind: Servicemetadata:  name: node-app-servicespec:  selector:    app: node-app  ports:    - protocol: TCP      port: 80      targetPort: 3000  type: ClusterIP

3.3. Running on the Cluster

Execute the commands (make sure you have kubectl configured and access to the cluster):

kubectl apply -f deployment.yamlkubectl app