Getting Started with Docker: A Practical Guide

Docker makes it easy to package applications and their dependencies into containers that run anywhere. This guide covers everything you need to get started.

Prerequisites

• A Linux server or Windows/Mac with Docker Desktop
• Basic terminal knowledge

Step 1: Install Docker

On Ubuntu/Debian:

curl -fsSL https://get.docker.com -o get-docker.sh
sudo sh get-docker.sh
sudo usermod -aG docker $USER

Log out and back in for the group change to take effect.

Verify installation:

docker --version
docker run hello-world

Step 2: Understand Key Concepts

• Image — A read-only template with your application and dependencies
• Container — A running instance of an image
• Dockerfile — Instructions to build an image
• Volume — Persistent storage for containers
• Network — Communication between containers

Step 3: Run Your First Container

# Run an Nginx web server
docker run -d -p 8080:80 --name my-web nginx
Check running containers
docker ps
View logs
docker logs my-web
Stop the container
docker stop my-web

Visit http://localhost:8080 to see the Nginx welcome page.

Step 4: Write a Dockerfile

Create a simple Node.js application:

mkdir my-app && cd my-app

Create app.js:

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello from Docker!');
});
server.listen(3000, () => console.log('Server running on port 3000'));

Create Dockerfile:

FROM node:20-alpine
WORKDIR /app
COPY app.js .
EXPOSE 3000
CMD ["node", "app.js"]

Build and run:

docker build -t my-app .
docker run -d -p 3000:3000 my-app

Step 5: Docker Compose

Create docker-compose.yml for multi-container apps:

version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data
volumes:
  pgdata:

docker compose up -d
docker compose logs
docker compose down

Essential Commands Cheat Sheet

• docker ps — List running containers
• docker ps -a — List all containers
• docker images — List images
• docker exec -it bash — Shell into a container
• docker rm — Remove a container
• docker rmi — Remove an image
• docker system prune — Clean up unused resources

Conclusion

You now understand Docker fundamentals and can build, run, and manage containers. Next steps: explore Docker networking, multi-stage builds, and container orchestration with Kubernetes.