Docker Compose vs. Docker CLI

Imagine you need to set up WordPress. This involves two main components: a database (like MySQL) and the WordPress application itself.

Docker CLI

Using only the Docker CLI, here's what you'd have to do:

1. Create a network: This allows the containers to talk to each other.

docker network create wordpress-network

2. Start the MySQL container:

docker run -d \
  --name db \
  --network wordpress-network \
  -e MYSQL_ROOT_PASSWORD=example_password \
  -e MYSQL_DATABASE=wordpress \
  -e MYSQL_USER=wordpress \
  -e MYSQL_PASSWORD=wordpress_password \
  -v db_data:/var/lib/mysql \
  mysql:5.7

3. Start the WordPress container:

docker run -d \
  --name wordpress \
  --network wordpress-network \
  -p 8000:80 \
  -e WORDPRESS_DB_HOST=db \
  -e WORDPRESS_DB_NAME=wordpress \
  -e WORDPRESS_DB_USER=wordpress \
  -e WORDPRESS_DB_PASSWORD=wordpress_password \
  -v wordpress_data:/var/www/html \
  wordpress:latest

4. Stopping the containers

docker stop wordpress
docker stop db

5. Removing the containers

docker rm wordpress
docker rm db

6. Removing the network:

docker network rm wordpress-network

As you can see, even for a simple two-container application, the CLI commands are lengthy, repetitive, and require careful attention to dependencies (the database must start before WordPress) - commands needs to be executed in a certain order.

Docker Compose

Now, let's see how Docker Compose simplifies this process.

1. Create a docker-compose.yml file: This file defines the entire application stack in a simple, readable format:

services:
  db:
    image: mysql:5.7
    restart: always
    environment:
      MYSQL_ROOT_PASSWORD: example_password
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD: wordpress_password
    volumes:
      - db_data:/var/lib/mysql
  wordpress:
    depends_on:
      - db
    image: wordpress:latest
    ports:
      - "8000:80"
    restart: always
    environment:
      WORDPRESS_DB_HOST: db
      WORDPRESS_DB_NAME: wordpress
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_PASSWORD: wordpress_password
    volumes:
      - wordpress_data:/var/www/html
volumes:
  db_data:
  wordpress_data:

2. Start the application: With one simple command:

docker compose up -d

That's it! This single command does everything we did with multiple CLI commands:

• Creates the network.
• Starts the MySQL container with the correct settings.
• Starts the WordPress container, linking it to the database.
• Maps ports and creates volumes.
• Handles dependencies automatically.

3. Stop and remove everything:

docker compose down

Key Takeaways:

• Configuration: Compose uses a single, declarative YAML file, making it much easier to manage and understand the application configuration.
• Dependencies: Compose handles dependencies automatically, ensuring containers start in the correct order.
• Commands: Compose uses simple, high-level commands, reducing the amount of typing and the risk of errors.

Docker Compose drastically simplifies managing multi-container applications, making development and deployment much more efficient. It's the recommended approach for most Docker projects involving more than one container.