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Multi-Container Application

Now let's put everything together by building a complete multi‑container application using Docker Compose. We'll create a simple web app with a Node.js frontend, a MongoDB database, and a volume for persistent data.

Application Overview

We'll build a simple todo app where users can add tasks. The stack:
  • Node.js: REST API that connects to MongoDB.
  • MongoDB: NoSQL database.
  • Volume: To persist MongoDB data.

Step 1: Create the Node.js App

Create a folder todo-app with a subfolder app. Inside app, create package.json and server.js.

package.json (minimal):
{
  "name": "todo-app",
  "version": "1.0.0",
  "dependencies": {
    "express": "^4.18.2",
    "mongoose": "^7.0.0"
  }
}
server.js:
const express = require('express');
const mongoose = require('mongoose');

const app = express();
app.use(express.json());

mongoose.connect('mongodb://db:27017/todo', { useNewUrlParser: true });

const Task = mongoose.model('Task', { name: String });

app.get('/tasks', async (req, res) => {
  const tasks = await Task.find();
  res.json(tasks);
});

app.post('/tasks', async (req, res) => {
  const task = new Task({ name: req.body.name });
  await task.save();
  res.json(task);
});

app.listen(3000, () => console.log('Server running on port 3000'));

Step 2: Create a Dockerfile for Node.js

Inside app, create Dockerfile:
FROM node:18-alpine
WORKDIR /app
COPY package*.json .
RUN npm install
COPY . .
CMD ["node", "server.js"]

Step 3: Write docker-compose.yml

In the root (todo-app), create docker-compose.yml:
services:
  app:
    build: ./app
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    depends_on:
      - db

  db:
    image: mongo:latest
    volumes:
      - mongo-data:/data/db

volumes:
  mongo-data:

Step 4: Run the Application

Navigate to the todo-app folder and run:
docker compose up --build -d
Check the logs:
docker compose logs -f app
Your API is available at http://localhost:3000/tasks. You can test with curl or Postman.

Testing the API

Add a task:
curl -X POST http://localhost:3000/tasks -H "Content-Type: application/json" -d '{"name":"Learn Docker"}'
List tasks:
curl http://localhost:3000/tasks

Cleanup

To stop and remove everything including the volume:
docker compose down -v


Two Minute Drill
  • Use Compose to combine a Node.js app, MongoDB, and a volume.
  • Service names are used as hostnames (e.g., db).
  • Build the app image with build: ./app and run with docker compose up --build.
  • Persist database data using a named volume.
  • Test the API with curl or a browser.

Need more clarification?

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