docker / awesome-compose

Docker Compose Fundamentals

This section focuses on the fundamental aspects of Docker Compose, outlining the structure of a docker-compose.yml file, the creation and management of multi-container applications, and how to leverage Docker Compose for local development and testing.

Defining Multi-container Applications

Docker Compose facilitates the definition of multi-container applications through a YAML file named docker-compose.yml. This file acts as a blueprint, specifying the services, networks, and volumes that comprise your application.

Example:

version: '3.8'  # Specify the Compose file version
          services:
            web:
              build: .  # Build the web service from the current directory
              ports:
                - "80:80"  # Expose port 80 on the host to port 80 in the container
              depends_on:
                - db  # Ensure the database service is started before the web service
            db:
              image: mysql:latest  # Use the latest MySQL image
              environment:
                MYSQL_ROOT_PASSWORD: password  # Set the MySQL root password

Explanation:

  • version: Specifies the Docker Compose file version.
  • services: Defines the individual services that constitute the application.
  • build: Instructs Compose to build an image from the specified directory.
  • ports: Maps ports between the host and the container.
  • depends_on: Ensures that the specified service is started before the current service.
  • image: Defines the image to use for the service.
  • environment: Sets environment variables for the service.

Defining Services, Networks, and Volumes

Services:

A service represents a container within your multi-container application. Each service is defined within the services section of the docker-compose.yml file.

Example:

services:
            web:
              image: nginx:latest
            db:
              image: postgres:latest

Networks:

Networks in Docker Compose provide a means for services to communicate with each other.

Example:

networks:
            app-net:  # Define a network named 'app-net'
              driver: bridge  # Use the 'bridge' network driver

Volumes:

Volumes in Docker Compose allow for persistent data storage, decoupling data from the container’s life cycle.

Example:

services:
            web:
              volumes:
                - data:/var/www/html  # Mount a volume named 'data' to the container's /var/www/html directory
          volumes:
            data:

Docker Compose Lifecycle

Docker Compose provides commands for managing the application’s lifecycle, including up, down, and restart.

docker-compose up: Starts and builds services defined in the docker-compose.yml file.

docker-compose down: Stops and removes containers, networks, and volumes created by docker-compose up.

docker-compose restart: Restarts the services defined in the docker-compose.yml file.

Using Docker Compose for Local Development and Testing

Docker Compose is a valuable tool for local development and testing, simplifying the process of managing and deploying multi-container applications.

Benefits of Docker Compose:

  • Simplified deployment: Compose streamlines the process of running and managing multi-container applications.
  • Consistent environment: Ensures a consistent development environment across different machines.
  • Improved workflow: Enables faster development cycles by automating common tasks.

Example:

docker-compose up -d  # Start the application in detached mode
          docker-compose exec web bash  # Access the web service's container shell
          docker-compose down  # Stop and remove the application

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