1. What Are We Building? (Explained Simply)

Every beginner understands Docker theoretical concepts but gets confused when building their first project.

So here is the easiest possible example:

👉 A tiny Node.js web server that prints: “Hello from Docker 🎉”

We will:

• Build the app
• Create Dockerfile
• Build Docker image
• Run container
• Map ports
• Use volume
• See logs
• And understand Docker’s full workflow

This one project will teach you how Docker actually works in real life.

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2. Project Structure (Visual)

random-docker-project/
│
├── server.js
└── Dockerfile

Simple. Clean. Beginner-friendly.

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3. Step 1 — Create the App (server.js)

Create a file named server.js:

const http = require("http");

const server = http.createServer((req, res) => {
  res.end("Hello from Docker 🎉");
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});

This is the easiest Node.js server ever.

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4. Step 2 — Create the Dockerfile

(Everything explained clearly)

Create Dockerfile:

# 1. Start with Node image
FROM node:18

# 2. Create working folder inside container
WORKDIR /app

# 3. Copy project files
COPY . .

# 4. Start the server
CMD ["node", "server.js"]

Visual Breakdown:

FROM node:18       → Borrow Node runtime
WORKDIR /app       → Like choosing your working desk
COPY . .           → Move files into container
CMD [...]          → Tell Docker what to run

This is your complete “recipe card”.

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🛠️ 5. Step 3 — Build the Docker Image

Run:

docker build -t random-app .

Visual:

Dockerfile → Image called "random-app"

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🚀 6. Step 4 — Run the Container

Run:

docker run -p 8080:3000 random-app

Visual Explanation:

8080 (your laptop) → 3000 (inside container)

Open browser:

http://localhost:8080

You will see:

**Hello from Docker **

Congratulations — you just containerized your first real app.

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7. Bonus: Add a Volume (For Live Editing)

Let’s connect your real folder to the container:

docker run -p 8080:3000 \
  -v $(pwd):/app \
  random-app

Now:

• Change server.js
• Refresh browser
• Changes apply instantly

This shows how developers use Docker in real projects.

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8. Visual Summary of the Entire Workflow

Your App (server.js)
      ↓
Dockerfile (instructions)
      ↓ docker build
Docker Image (package)
      ↓ docker run
Container (running app)
      ↓
Browser (Hello from Docker 🎉)

Once you understand this pipeline, Docker becomes EASY.

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9. Why This Example Helps You Understand Docker Properly

✔ You saw how to build a real working app

✔ You created a Dockerfile

✔ You built your own Docker image

✔ You understood port mapping

✔ You used a volume

✔ You saw logs

This covers 90% of Docker knowledge beginners need.

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**10. FAQ **

Q1. Why do we map ports like 8080:3000?

Because the app inside container runs on port 3000, but your computer listens on 8080.

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Q2. Why do we need a Dockerfile?

So Docker knows how to package your app — like a recipe.

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Q3. Can I run multiple containers from the same image?

Yes. The image is reusable.

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Q4. Why do we use -v volume?

To keep your data/code outside the container, safe and editable.

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Q5. What happens when I stop the container?

Container stops → image remains → your code remains. (Unless you delete everything manually.)

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🏁 Final Words

This one small project teaches everything:

How Docker builds, runs, stores, maps, and serves your apps.

Docker looks complicated only until you build your first project. After that, you realize:

“It’s just a smart box running my app anywhere I want.”

This is exactly what Docker by Example is for — making Docker simple, visual, and practical.