Docker Hello World

What you'll build

You'll install Docker and create your first container: a Node.js app packaged to work identically on any computer. You'll learn to run Ubuntu containers, databases like PostgreSQL, and use volumes to avoid losing data. When you're done, you'll have a Dockerized app with its Dockerfile, docker-compose.yml, and the ability to spin up services with one command. It's the foundation for working in teams where "it works on my machine" will no longer be a problem.

Step 1: Install Docker

Verify:

docker --version
docker run hello-world

⚠️ Windows: You need WSL2 enabled. Docker Desktop guides you through installation.

Step 2: Your first container

# Download and run Ubuntu in seconds
docker run -it ubuntu bash

# Now you're INSIDE the container
cat /etc/os-release   # You'll see "Ubuntu"
apt update            # Works like real Linux
exit                  # Exit the container

What happened? Docker downloaded an Ubuntu image (~30MB, not 4GB) and ran it isolated from your system.

Step 3: Run useful services

Docker shines when you need databases or services without permanent installation:

# PostgreSQL ready in 10 seconds
docker run -d --name my-postgres \
  -e POSTGRES_PASSWORD=secret \
  -p 5432:5432 \
  postgres:16-alpine

# Redis for caching
docker run -d --name my-redis -p 6379:6379 redis:alpine

# Adminer (web interface for databases)
docker run -d --name adminer -p 8080:8080 adminer

Open http://localhost:8080 to see Adminer running.

⚠️ PROBLEM: If you run docker rm my-postgres, you lose ALL the data. Keep reading to fix this.

Step 4: Volumes (Persistent Data)

The most common beginner mistake: They create a database, save data, remove the container... and lose everything.

Why does this happen?

WITHOUT VOLUME:
┌─────────────────────────┐
│      Container          │
│  ┌─────────────────┐    │
│  │    Database     │    │  ← Data lives INSIDE
│  │   (your data)   │    │     the container
│  └─────────────────┘    │
└─────────────────────────┘
        ↓
   docker rm postgres
        ↓
   💀 DATA LOST

WITH VOLUME:
┌─────────────────────────┐      ┌─────────────────┐
│      Container          │      │     Volume      │
│  ┌─────────────────┐    │ ──── │  (your disk)    │
│  │    Database     │────│──────│   your data     │
│  └─────────────────┘    │      └─────────────────┘
└─────────────────────────┘              ↓
        ↓                         Data is stored
   docker rm postgres             OUTSIDE container
        ↓                                ↓
   Container removed              ✅ DATA SAFE

Create PostgreSQL with persistent volume

# Create a named volume
docker volume create postgres_data

# Run PostgreSQL using that volume
docker run -d --name my-postgres \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_USER=dev \
  -e POSTGRES_DB=myapp \
  -p 5432:5432 \
  -v postgres_data:/var/lib/postgresql/data \
  postgres:16-alpine

The magic is in -v postgres_data:/var/lib/postgresql/data:

• postgres_data = volume name on your machine
• /var/lib/postgresql/data = where Postgres stores data inside the container

Test that it works

# Connect and create a table
docker exec -it my-postgres psql -U dev -d myapp -c "CREATE TABLE test (id INT);"
docker exec -it my-postgres psql -U dev -d myapp -c "INSERT INTO test VALUES (1), (2), (3);"

# Remove the container
docker stop my-postgres && docker rm my-postgres

# Create a new one with the SAME volume
docker run -d --name my-postgres \
  -e POSTGRES_PASSWORD=secret \
  -e POSTGRES_USER=dev \
  -e POSTGRES_DB=myapp \
  -p 5432:5432 \
  -v postgres_data:/var/lib/postgresql/data \
  postgres:16-alpine

# Verify the data is still there
docker exec -it my-postgres psql -U dev -d myapp -c "SELECT * FROM test;"
# Result: 1, 2, 3 ✅

Volume commands

Mount types

Bind Mount example for development:

# Your local code syncs with the container
docker run -d --name my-app \
  -v $(pwd):/app \
  -p 3000:3000 \
  node:20-alpine npm start

Change a file → the container sees it immediately.

Step 5: Create your own image

Now that you understand containers and volumes, create your own image.

Create a docker-hello folder with these 3 files:

Dockerfile:

FROM node:20-alpine
WORKDIR /app
COPY package*.json ./
RUN npm install
COPY . .
CMD ["node", "index.js"]

index.js:

console.log("Hello from Docker! 🐳");
console.log("Date:", new Date().toISOString());
console.log("Node version:", process.version);

package.json:

{ "name": "docker-hello", "version": "1.0.0" }

Build and run:

docker build -t my-app .
docker run my-app

Step 6: Install Portainer (Visual Management)

Portainer is a web interface for Docker. Perfect for beginners:

# Create a volume to persist data
docker volume create portainer_data

# Install Portainer
docker run -d -p 9000:9000 \
  --name portainer \
  --restart=always \
  -v /var/run/docker.sock:/var/run/docker.sock \
  -v portainer_data:/data \
  portainer/portainer-ce:latest

Open http://localhost:9000 and create your admin user.

What can you do with Portainer?

• See all your containers in a table
• Start/stop/remove with one click
• View logs in real-time
• Create containers without commands
• Manage images, volumes, networks

💡 Tip: Keep Portainer running always. It's like "Finder" or "Explorer" but for Docker.

🛠️ Management tools

For production deployment

🎯 Recommendation for beginners: Use Portainer to learn, then EasyPanel or Coolify when you want easy deployment.

Essential commands

If something failed

What you learned

✅ Install Docker and verify it works ✅ Run pre-made containers (Ubuntu, Postgres, Redis) ✅ Use volumes to not lose data (beginner's #1 mistake) ✅ Create your own image with Dockerfile ✅ Use Portainer for visual management ✅ Essential commands for daily use

Next steps

→ Consume a JSON API — Connect your app with real data → Deploy with Docker — Take your container to production → Docker Basics (theory) — Understand containers vs VMs