docker-compose-yaml.md

Docker Compose YAML File Format

A docker-compose.ymal file is used to define and run multi-container Docker applications. Here’s a basic example and an overview of the format and options available.

Basic Example

version: '3.8'
services:
  frontend:
    image: node:14
    working_dir: /usr/src/app
    volumes:
      - ./frontend:/usr/src/app
    ports:
      - "3000:3000"
    command: npm start

  backend:
    image: python:3.8
    working_dir: /usr/src/app
    volumes:
      - ./backend:/usr/src/app
    ports:
      - "5000:5000"
    command: python app.py

  db:
    image: postgres:13
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
      POSTGRES_DB: mydatabase
    ports:
      - "5432:5432"
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data:

Main Sections and Options

1. Version: Specifies the version of the Docker Compose file format.

   version: '3.8'

2. Services: Defines the services that make up your application.

   services:
     service_name:
       option1: value1
       option2: value2

3. Service Configuration Options:

   • image: Specifies the image to use for the service.

     image: image_name:tag

   • build: Specifies the build context for the service.

     build:
       context: ./path_to_dockerfile
       dockerfile: Dockerfile

   • command: Overrides the default command for the container.

     command: your_command

   • ports: Maps ports between the host and the container.

     ports:
       - "host_port:container_port"

   • volumes: Mounts host paths or named volumes.

     volumes:
       - ./host_path:/container_path
       - volume_name:/container_path

   • environment: Sets environment variables.

     environment:
       - ENV_VAR_NAME=value

   • depends_on: Specifies dependencies between services.

     depends_on:
       - service_name

   • networks: Configures networks for the service.

     networks:
       - network_name

4. Volumes: Defines named volumes that can be used by services.

   volumes:
     volume_name:

5. Networks: Defines custom networks for the services.

   networks:
     network_name:

Advanced Example

Here’s a more complex example that includes additional options like environment variables, custom networks, and more:

version: '3.8'

services:
  frontend:
    build:
      context: ./frontend
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    environment:
      - REACT_APP_API_URL=http://backend:5000
    networks:
      - frontend_net
      - backend_net

  backend:
    build:
      context: ./backend
      dockerfile: Dockerfile
    ports:
      - "5000:5000"
    environment:
      - DATABASE_URL=postgres://user:password@db:5432/mydatabase
    depends_on:
      - db
    networks:
      - backend_net

  db:
    image: postgres:13
    environment:
      POSTGRES_USER: user
      POSTGRES_PASSWORD: password
      POSTGRES_DB: mydatabase
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - backend_net

volumes:
  db-data:

networks:
  frontend_net:
  backend_net:

Key Commands for Docker Compose

• Start services:

  docker-compose up

  Add the -d flag to run containers in detached mode:

  docker-compose up -d

• Stop services:

  docker-compose down

• Rebuild services:

  docker-compose up --build

• View logs:

  docker-compose logs

• Scale services:

  docker-compose up --scale service_name=num

• Execute a command in a running container:

  docker-compose exec service_name command

This should provide you with a comprehensive understanding of how to write and use a docker-compose.yml file.