01 — Choose a simple app to containerize

Category: Dockerfile · Priority: High · Step: 2

Keep it minimal — a single route returning JSON is enough. The focus is the Docker setup, not the app.

🎯 What is this task?

Before writing any Docker code, you need a real app to containerize. Don't build something complex — a single web page that returns a message is enough. The goal here is to have working code you can wrap in Docker.

🤖 AI Prompt to generate the app

Copy and paste this into Claude or ChatGPT:

"Create a simple Node.js Express app. It should have two routes: GET / that returns a JSON response { "message": "Hello from Docker!" }, and GET /health that returns { "status": "ok" }. Use port 3000. Put everything in a single file called index.js. Also create a package.json for it."

📋 Step-by-step

Step 1 — Install Node.js (if not installed)

Go to https://nodejs.org and download the LTS version. After installing, verify it works:

node --version
npm --version

Both commands should print a version number.

Step 2 — Create a project folder

mkdir my-docker-app
cd my-docker-app

Step 3 — Create the files

Create index.js with this content:

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

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

app.get('/health', (req, res) => {
  res.json({ status: 'ok' });
});

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

Create package.json with this content:

{
  "name": "my-docker-app",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  },
  "dependencies": {
    "express": "^4.18.2"
  }
}

Step 4 — Install dependencies and test it locally

npm install
npm start

Open your browser and go to http://localhost:3000 — you should see the JSON response. Press Ctrl+C to stop.

✅ Done when

• You have an index.js and package.json in your folder
• Running npm start shows the server running message
• http://localhost:3000 shows { "message": "Hello from Docker!" }
• http://localhost:3000/health shows { "status": "ok" }