Containerizing a Node js Application: From Source Code to Docker Image

Moving your Nodejs application from your local machine into a Docker container is one of the best ways to ensure environment consistency between the development and production.

No more "It works on my machine " excuses !!

Step 1: Prepare an Node js application

Example

// index.js 
const express = require('express'); 
const app = express(); 
const PORT = process.env.PORT || 3000;

app.get('/', (req, res) => {
 res.json({ message: "Hello from inside the Docker container!" }); 
});

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

Update your package.json to include a start script

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

Step 2: Create a .dockerignore File Before copying files into your docker image, we wnat to prevent unnecessary files from bloating the image.

node_modules
npm-debug.log
.git

Step 3: Write the Dockerfile

Dockerfile is a blueprint that tells Docker how to build your application image. Create file named Dockerfile in your project root:

FROM node:20-alpine

WORKDIR: /usr/src/app

COPY package*.json .

RUN npm ci --only=production

COPY . .

EXPOSE 3000

CMD ["npm","start"]

Step 4: Build the Docker Image To build Dockerfile use this command

docker build -t my-node-app:1.0 .

Step 5: Run the Container

To run the Docker Image use this command

docker run -d -p 8080:3000 --name node-app-container my-node-app:1.0