Docker Compose

Docker Compose is a tool that allows you to define and manage multi-container Docker applications. It enables the deployment of multiple containers defined in a single docker-compose.yml file, simplifying the management of complex containerized environments.

Key Features of Docker Compose

1. Service Definition: Docker Compose allows you to define multiple services in a single YAML file. Each service can be run as a separate container.
2. Network and Volume Management: It enables the definition of networks and volumes that can be shared between containers.
3. Automation: Allows for the automatic building and running of containers, simplifying CI/CD processes.
4. Orchestration: Enables orchestration of containers in various environments, making it easier to manage complex applications.

Docker Compose Use Cases

1. Simple Web Application

You can use Docker Compose to run a simple web application consisting of an Nginx server and a Node.js backend.

docker-compose.yml File:

version: '3'
services:
  web:
    image: nginx:latest
    ports:
      - "80:80"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf
  backend:
    image: node:14
    working_dir: /app
    volumes:
      - ./app:/app
    command: npm start

Directory Structure:

.
├── app
│ └── index.js
├── docker-compose.yml
└── nginx.conf

Starting the Application:

docker-compose up -d

This command starts both the Nginx server and the Node.js backend.

2. Application with a Database

Docker Compose is ideal for running applications that require a database, such as a web application with a MySQL database.
It's important to note that running databases in containers isn't always desirable, depending on the use case. Always consider whether running the database in a container is the right choice.

docker-compose.yml File:

version: '3'
services:
  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: example
  wordpress:
    image: wordpress:latest
    ports:
      - "8000:80"
    environment:
      WORDPRESS_DB_HOST: db:3306
      WORDPRESS_DB_PASSWORD: example
    depends_on:
      - db

Starting the Application:

docker-compose up -d

This command starts MySQL and WordPress containers, automatically configuring the connection between them.

Basic Docker Compose Commands

1. Start Services:

   docker-compose up

2. Start Services in the Background:

   docker-compose up -d

3. Stop Services:

   docker-compose stop

4. Stop and Remove Containers, Networks, and Volumes:

   docker-compose down

5. View Logs:

   docker-compose logs

Summary

Docker Compose is a powerful tool for managing complex containerized applications, allowing for easy definition, deployment, and management of multi-container environments. Its ability to orchestrate various services in a single YAML file makes it indispensable in the modern application lifecycle.