How to Dockerize a Node.js Application Step by Step

In modern web development, Docker has become an indispensable tool for building, shipping, and running applications. By Dockerizing your Node.js application, you can make it portable, consistent across different environments, and easy to manage.

On this Papayacoders website, we will walk you through every step of containerizing a simple Node.js app.

Dockerize a Node.js Application

Before we begin, make sure you have:-

• Node.js installed (for local testing)
• Docker is installed and running
• A basic understanding of Node.js and Express

Step 1: Create a Simple Node.js Application

Start by creating a new project folder:

mkdir docker-node-app
cd docker-node-app

Initialize a new Node project:

npm init -y

Install Express:

npm install express

Now, create the main app file.

index.js

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

app.get('/', (req, res) => {
  res.send('Hello from Dockerized Node.js!');
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
  console.log(`Server is running on port ${PORT}`);
});

Step 2: Create a package.json (Auto-generated with npm init)

Make sure your package.json Includes the start script:

"scripts": {
  "start": "node index.js"
}

Step 3: Create a .dockerignore File

Exclude files/folders you don’t want in the Docker image:

.dockerignore

node_modules
npm-debug.log

Step 4: Create the Dockerfile

This file defines how your Docker image should be built.

Dockerfile

# Use the official Node.js image
FROM node:18-alpine

# Create app directory
WORKDIR /app

# Copy package.json and install dependencies
COPY package*.json ./
RUN npm install

# Copy the rest of the application
COPY . .

# Expose the port the app runs on
EXPOSE 3000

# Start the application
CMD ["npm", "start"]

Step 5: Build the Docker Image

Run this command in your project directory:

docker build -t node-docker-app .

This command:

• Reads the Dockerfile
• Installs dependencies
• Creates an image named node-docker-app

Step 6: Run the Docker Container

Now run your container:

docker run -p 3000:3000 node-docker-app

Open your browser and visit:

http://localhost:3000

You should see: “Hello from Dockerized Node.js!”

Step 7: Stop and Clean Up

To stop the container, press Ctrl + C.

To list running containers:

docker ps

To stop and remove a container:

docker stop <container_id>
docker rm <container_id>

To remove the image:

docker rmi node-docker-app

Use Docker Compose (Optional)

If your app uses databases (like MongoDB), Docker Compose helps manage multiple containers.

Create a docker-compose.yml:

version: '3'
services:
  app:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
    environment:
      - NODE_ENV=development

Run it using:

docker-compose up

Benefits of Dockerizing Node.js Apps

Conclusion:-

In simple terms, conclusion, you should know that Dockerizing a Node.js application helps streamline the development and deployment processes. By following the steps above, you can easily package your Node.js app into a container and run it reliably anywhere.

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