Docker in 30 Minutes: From Install to First Container

Docker lets you package your application with everything it needs into a lightweight container that runs anywhere. No more "it works on my machine." Let's get you from zero to a running container in 30 minutes.

What Problem Does Docker Solve?

Before Docker: you install Python 3.11, your teammate uses 3.10, the server runs 3.9. Your app uses PostgreSQL 15, but production is on 14. Dependency hell. Docker wraps your app AND its exact environment into one portable unit — a container.

Installation

Download Docker Desktop from docker.com. It includes Docker Engine, CLI, Docker Compose, and a GUI dashboard. Verify:

docker --version
docker run hello-world   # should print a welcome message

Core Concepts

Your First Container

# Run nginx web server in a container
docker run -d -p 8080:80 --name my-nginx nginx

# Visit http://localhost:8080 — you'll see the nginx welcome page!

# What's running?
docker ps

# Stop it
docker stop my-nginx

# Remove it
docker rm my-nginx

Writing a Dockerfile

Create a simple Python app:

# app.py
from flask import Flask
app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello from Docker!'

if __name__ == '__main__':
    app.run(host='0.0.0.0', port=5000)

# Dockerfile
FROM python:3.12-slim          # start from a Python image
WORKDIR /app                    # set working directory
COPY requirements.txt .         # copy dependency list
RUN pip install -r requirements.txt
COPY . .                        # copy everything else
EXPOSE 5000                     # document what port we use
CMD ["python", "app.py"]        # what to run on start

# requirements.txt
flask==3.1.0

# Build and run
docker build -t my-python-app .
docker run -d -p 5000:5000 my-python-app

Essential Commands

docker ps                  # list running containers
docker ps -a               # list ALL containers
docker images              # list images
docker logs <container>    # view logs
docker exec -it <c> bash   # shell into a running container
docker rm <container>      # remove a container
docker rmi <image>         # remove an image
docker system prune -a     # clean up everything unused

Docker Compose (Multi-Container Apps)

# docker-compose.yml
version: '3.8'
services:
  web:
    build: .
    ports:
      - "5000:5000"
    depends_on:
      - db
  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: secret
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:

docker compose up -d       # start everything
docker compose down        # stop everything

Docker vs VM

Containers share the host OS kernel, so they start in milliseconds and use minimal RAM. VMs each need their own OS, taking gigabytes. For most web apps, Docker is the clear winner.