Docker Compose

Docker Compose Cheat Sheet

Overview

Docker Compose is a tool used to define and manage multi-container Docker applications. With docker-compose.yml, you can configure all your application's services (e.g., app, database, cache) in a single YAML file and run them together.

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Installation

Install Docker Compose (if not included in Docker Desktop)

1. Download Docker Compose:

   sudo curl -L "https://github.com/docker/compose/releases/download/v2.16.0/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose

2. Make it executable:

   sudo chmod +x /usr/local/bin/docker-compose

3. Verify installation:

   docker-compose --version

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docker-compose.yml File Structure

A typical docker-compose.yml file has the following structure:

version: '3.8' # Define the Compose file format version

services:
  <service_name>:
    image: <image_name>
    build: <build_context>
    ports:
      - "<host_port>:<container_port>"
    volumes:
      - "<host_path>:<container_path>"
    environment:
      <key>: <value>
    depends_on:
      - <other_service_name>

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Docker Compose Commands

Command	Description
docker-compose up	Build and start containers.
docker-compose up -d	Start containers in detached mode (background).
docker-compose down	Stop and remove containers, networks, and volumes.
docker-compose build	Build or rebuild services.
docker-compose ps	List running containers.
docker-compose logs	Show logs for containers.
docker-compose stop	Stop running containers without removing them.
docker-compose restart	Restart services.

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Example: Multi-Service Application

docker-compose.yml

This example creates a Node.js application with a MongoDB database:

version: '3.8'

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=development
    depends_on:
      - db

  db:
    image: mongo:4.4
    container_name: mongodb
    ports:
      - "27017:27017"
    volumes:
      - mongo_data:/data/db

volumes:
  mongo_data:

Steps to Run

1. Create a Dockerfile for the app service:

   FROM node:16
   
   WORKDIR /app
   
   COPY package*.json ./
   RUN npm install
   
   COPY . .
   
   EXPOSE 3000
   CMD ["npm", "start"]

2. Run docker-compose up to start both services:

   docker-compose up

3. Access the application at http://localhost:3000.

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Best Practices for Using Docker Compose

1. Version Pinning: Always specify the Compose version (e.g., version: '3.8') for compatibility.
2. Use .env Files: Store environment variables in a .env file for easier management:
   • Example .env file:

     NODE_ENV=production
     DB_HOST=mongodb

   • Reference in docker-compose.yml:

     environment:
       - NODE_ENV=${NODE_ENV}
       - DB_HOST=${DB_HOST}

3. Leverage Volumes: Use named volumes for persistent data.
4. Use Networks for Isolation: Specify networks to isolate services when needed.

   networks:
     default:
       name: custom_network

5. Keep docker-compose.yml Clean: Use separate Compose files for development and production:

   docker-compose -f docker-compose.dev.yml up

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Advanced Example: WordPress with MySQL

docker-compose.yml

version: '3.8'

services:
  wordpress:
    image: wordpress:latest
    ports:
      - "8080:80"
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_USER: user
      WORDPRESS_DB_PASSWORD: password
      WORDPRESS_DB_NAME: wordpress
    depends_on:
      - db

  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: rootpassword
      MYSQL_DATABASE: wordpress
      MYSQL_USER: user
      MYSQL_PASSWORD: password
    volumes:
      - db_data:/var/lib/mysql

volumes:
  db_data:

Steps to Run

1. Save the above configuration as docker-compose.yml.
2. Run the setup:

   docker-compose up

3. Access WordPress at http://localhost:8080.

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Debugging with Docker Compose

• Check logs of a specific service:

  docker-compose logs <service_name>

• Execute a command inside a running container:

  docker-compose exec <service_name> <command>

  Example:

  docker-compose exec app bash