Deploying JavaScript on Kubernetes: A Basic Guide for Beginners

Introduction: Why Deploy JavaScript on Kubernetes?

Modern web development is unthinkable without containerization. If you write in JavaScript (Node.js) and want your application to run stably, scale automatically, and be fault-tolerant — Kubernetes (K8s) will become your best friend.

Kubernetes is a container orchestration platform. It manages the deployment, scaling, and operation of your applications. In this guide, we will walk through the basic deployment of a simple Node.js application on Kubernetes. You will learn how to package your code into a Docker image, create a Pod, Service, and Deployment.

This article is intended for beginners. It is assumed that you already have Docker and Minikube installed (or access to a K8s cluster).

Step 1: Preparing the Node.js Application and Docker Image

First, let's create a simple web application using Express. It will respond to HTTP requests.

1.1. Application Code (app.js)

Create a file app.js:

const express = require('express');\nconst app = express();\nconst PORT = process.env.PORT || 3000;\n\napp.get('/', (req, res) => {\n  res.send('Hello from Kubernetes!');\n});\n\napp.listen(PORT, () => {\n  console.log(`Server running on port ${PORT}`);\n});\n

1.2. package.json File

Create package.json:

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

1.3. Dockerfile

Now let's create a Dockerfile to build the image:

FROM node:18-alpine\n\nWORKDIR /usr/src/app\n\nCOPY package*.json ./\nRUN npm install\n\nCOPY . .\n\nEXPOSE 3000\n\nCMD ["node", "app.js"]\n

1.4. Building and Pushing the Image

Run the commands:

docker build -t my-node-app:v1 .\n

If you are using Minikube, build the image inside its environment:

minikube image build -t my-node-app:v1 .\n

Or push the image to Docker Hub/any registry and specify it in the manifest.

Step 2: Basic Kubernetes Objects (Pod, Deployment, Service)

Kubernetes works with objects. For deployment, we will need three main ones:

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• Pod — the smallest unit, one or more containers.
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• Deployment — manages Pods, provides scaling and updates.
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• Service — a stable access point to Pods (usually via ClusterIP or NodePort).
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2.1. Creating a Deployment

Create a file deployment.yaml:

apiVersion: apps/v1\nkind: Deployment\nmetadata:\n  name: node-app-deployment\nspec:\n  replicas: 3\n  selector:\n    matchLabels:\n      app: node-app\n  template:\n    metadata:\n      labels:\n        app: node-app\n    spec:\n      containers:\n      - name: node-app\n        image: my-node-app:v1\n        ports:\n        - containerPort: 3000\n        env:\n        - name: PORT\n          value: "3000"\n

Explanation:

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• replicas: 3 — we will run 3 copies of the application for fault tolerance.
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• selector and labels — link the Deployment to the Pods.
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• image — the name of your Docker image.
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2.2. Creating a Service

Create a file service.yaml to access the application:

apiVersion: v1\nkind: Service\nmetadata:\n  name: node-app-service\nspec:\n  selector:\n    app: node-app\n  ports:\n    - protocol: TCP\n      port: 80\n      targetPort: 3000\n  type: NodePort\n

What is happening here:

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• The Service redirects traffic from port