Learn Docker & Docker Compose

2025-04-03 · 465 words · 3 minutes ·

A concise guide to Docker and Docker Compose for containerizing and managing applications.*

Introduction

Docker lets you package applications into containers—lightweight, portable, and consistent environments. Docker Compose allows you to define and run multi-container applications.

1. Check Docker Installation

docker --version                  # Show Docker version
docker info                       # Display Docker system-wide information

Use these to verify that Docker is correctly installed and running.

2. Basic Docker Commands

docker run hello-world           # Run a test container to verify setup
docker ps                        # List running containers
docker ps -a                     # List all containers (running and stopped)
docker images                    # List downloaded container images
docker rm <container_id>         # Remove a stopped container
docker rmi <image_id>            # Remove an image

These commands help you work with containers and manage their lifecycle.

3. Running Containers

docker run -it ubuntu bash       # Run an interactive shell inside Ubuntu

-it makes the container interactive (like SSH), and bash is the shell command you want to run.

docker run -d -p 8080:80 nginx   # Run Nginx in detached mode and map port 80 to 8080

-d runs in the background (detached), and -p maps ports from container to host.

4. Building Images

# Dockerfile
FROM python:3.10-slim
COPY . /app
WORKDIR /app
RUN pip install -r requirements.txt
CMD ["python", "app.py"]

docker build -t my-python-app .  # Build image from Dockerfile in current directory
docker run my-python-app         # Run container from the built image

This defines and builds a custom image for your Python app.

5. Docker Volumes

docker volume create mydata                   # Create a volume
docker run -v mydata:/data ubuntu             # Mount volume into container

Volumes are used for persistent data storage independent of the container lifecycle.

6. Docker Compose Basics

# docker-compose.yml
version: "3.8"
services:
  web:
    image: nginx
    ports:
      - "8080:80"
  redis:
    image: redis

docker-compose up                  # Start services defined in the compose file
docker-compose down                # Stop and remove containers

Compose allows you to manage multi-container setups with a single file.

7. Common Compose Options

docker-compose up -d              # Run in detached mode
docker-compose ps                 # List running services
docker-compose logs               # View logs from services
docker-compose exec web bash      # Execute command in running container

Useful for monitoring and interacting with your services.

8. Environment Variables

# .env
APP_ENV=production

# docker-compose.yml
services:
  app:
    image: my-app
    environment:
      - APP_ENV=${APP_ENV}

Using .env files helps manage config across environments cleanly.

9. Docker Networks

docker network create my-net        # Create a custom network
docker run --network my-net ...     # Connect container to network

Containers on the same custom network can communicate using service names.

10. Clean Up Resources

docker system prune                 # Remove unused data (containers, images, networks)
docker-compose down --volumes      # Remove volumes too

Use this to reclaim space and avoid clutter.

Conclusion

Docker and Docker Compose simplify application packaging and multi-service orchestration. Learn these tools to build reproducible and scalable environments.

Happy containerizing! 🐳