Skip to main content

Docker and Docker Compose

What is Docker?​

Docker is a platform that allows developers to build, ship, and run applications in containers. Containers package your application code along with its dependencies, making it portable and consistent across environments.

Why Use Docker?​

  • Consistency Across Environments: Docker ensures your app runs the same in development, staging, and production.
  • Simplified Configuration: Run everything your app needs in isolated containers.
  • Portability: Move your application easily between systems.
  • Efficient Resource Usage: Containers are lightweight and faster to start compared to virtual machines.
  • Microservices Support: Run different services in separate containers, ideal for modular architectures.

Performance Benefits​

  • Lightweight: Containers share the host OS kernel, reducing overhead.
  • Speed: Builds and deployments are significantly faster than with full VMs.
  • Resource Control: Docker allows limiting CPU and memory usage per container.
  • Efficient Scaling: Easy to scale out services using container orchestration tools.

Docker Concepts​

  • Image: A blueprint of your application with all required dependencies.
  • Container: A running instance of an image.

Docker Compose: Managing Multi-Container Applications​

Docker Compose is a tool for defining and running multi-container Docker applications using a docker-compose.yml file.

Benefits:​

  • Manage multiple services (e.g., web, database) easily.
  • Define networks, volumes, and environment variables.
  • Useful for local development and testing.

Sample docker-compose.yml​

services:
  db:
    image: postgres:15
    env_file: .env
    volumes:
      - db_data:/var/lib/postgresql/data
    ports:
      - '5432'
  web:
    image: node:lts
    working_dir: /home/node/app
    environment:
      - NODE_ENV=development
    ports:
      - '3000:3000'
    volumes:
      - ./:/home/node/app
    depends_on:
      - db
    command: 'npm start'
volumes:
  db_data:

Explanation​

  • Volumes:

    • db_data is a named volume used to persist PostgreSQL data.
    • App volume mounts the current directory into the container for live-reloading during development.

  • Network:

    • Docker Compose automatically sets up a shared network so services can communicate using service names (e.g., db).

Running Docker Compose​

  1. Start all services:

    docker-compose up

  2. Stop all services:

    docker-compose down

  3. Stop all services and delete volumes:

    docker-compose down -v

    or

    docker-compose down --volumes

Reflection Questions​

  • Why might Docker be a better alternative to traditional virtual machines for development and deployment?
  • How does the use of environment variables in docker-compose.yml promote better configuration management?
  • What does it mean that containers are isolated, and how does this benefit application security or development workflows?

Summary​

  • Docker simplifies deployment and environment management.
  • Docker Compose makes it easy to manage multi-container setups.
  • Both tools are widely adopted in DevOps and Agile workflows.

For more information, visit the official Docker documentation.

Disclaimer: Generative AI was used in part to generate these lecture notes.