docker-compose

Docker Compose: Overview and Configurations

What is Docker Compose?

Docker Compose is a tool for defining and running multi-container Docker applications. With Docker Compose, you can use a YAML file to configure your application’s services, networks, and volumes. Then, with a single command, you can create and start all the services from your configuration.

Uses of Docker Compose

• Simplified Multi-Container Management: Easily manage multiple containers as a single application.
• Reproducible Environments: Define the exact environment in code, ensuring consistent setup across different environments (development, testing, production).
• Service Orchestration: Define dependencies between services, ensuring they start in the correct order.
• Configuration Versioning: Keep your environment configurations in version control along with your application code.

Key Docker Compose Commands

• docker-compose up: Create and start containers.
• docker-compose down: Stop and remove containers, networks, images, and volumes.
• docker-compose build: Build or rebuild services.
• docker-compose logs: View output from containers.
• docker-compose exec: Execute a command in a running container.

Question

What is the difference between docker-compose up and docker-compose build? Does up also builds the containers?

Success

Yes it does, if it does not already exists

Docker Compose Configuration File (docker-compose.yml)

The docker-compose.yml file is where you define your application’s services, networks, and volumes. Below are some common configurations you can use:

Services

Defines the services (containers) in your application.

services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    volumes:
      - ./webdata:/usr/share/nginx/html
    networks:
      - webnet
  db:
    image: postgres:latest
    environment:
      POSTGRES_PASSWORD: example
    volumes:
      - dbdata:/var/lib/postgresql/data
    networks:
      - webnet

Volumes

Defines named volumes to persist data.

volumes:
  dbdata:

Networks

Defines custom networks to enable communication between containers.

networks:
  webnet:

Common Configuration Options

image

Specifies the Docker image to use for the service.

image: nginx:latest

build

Specifies the build context and Dockerfile for the service.

build:
  context: ./path
  dockerfile: Dockerfile

ports

Maps ports between the host and the container.

ports:
  - "8080:80"

Note

The mapping is host:container, ie. container exposes port 80 which is mapped to port 8080 on the host machine

volumes

Mounts host directories or named volumes into the container.

volumes:
  - ./host_directory:/container_directory
  - dbdata:/var/lib/postgresql/data

environment

Sets environment variables for the container.

environment:
  - POSTGRES_PASSWORD=example

depends_on

Specifies service dependencies, ensuring they start in the correct order.

depends_on:
  - db

networks

Connects services to custom networks.

networks:
  - webnet

command

Overrides the default command for the service’s container.

command: ["bundle", "exec", "puma"]

Full Example docker-compose.yml

version: '3.8'
 
services:
  web:
    build:
      context: .
      dockerfile: Dockerfile
    image: my_user/web:latest
    ports:
      - "8080:80"
    volumes:
      - ./webdata:/usr/share/nginx/html
    networks:
      - webnet
    depends_on:
      - db
  db:
    image: postgres:latest
    environment:
      POSTGRES_PASSWORD: example
    volumes:
      - dbdata:/var/lib/postgresql/data
    networks:
      - webnet
 
volumes:
  dbdata:
 
networks:
  webnet:

Summary

Docker Compose simplifies the management of multi-container Docker applications by allowing you to define and run your services with a single command. You can configure various aspects of your application, including services, networks, and volumes, in the docker-compose.yml file.