G
GuideDevOps
Lesson 8 of 13

Docker Compose

Part of the Docker tutorial series.

Docker Compose allows you to define a multi-container environment (like a Web server + Database) in a single file and start them all with one command.

1. The docker-compose.yaml File

Let's look at a typical Compose file for a web application and its database.

docker-compose.yaml:

version: '3.8'
 
services:
  web:
    image: nginx:latest
    ports:
      - "8080:80"
    depends_on:
      - db
    networks:
      - app-network
 
  db:
    image: postgres:14
    environment:
      POSTGRES_PASSWORD: mysecretpassword
    volumes:
      - db-data:/var/lib/postgresql/data
    networks:
      - app-network
 
networks:
  app-network:
    driver: bridge
 
volumes:
  db-data:

2. Using Docker Compose

Start the Services

Action:

docker-compose up -d

Result:

Creating network "my-app_app-network" with driver "bridge"
Creating volume "my-app_db-data" with default driver
Creating my-app_db_1  ... done
Creating my-app_web_1 ... done

Check Running Services

Action:

docker-compose ps

Result:

    Name               Command               State           Ports         
---------------------------------------------------------------------------
my-app_db_1    docker-entrypoint.sh po...   Up      5432/tcp               
my-app_web_1   /docker-entrypoint.sh n...   Up      0.0.0.0:8080->80/tcp

Stop and Cleanup

Action:

docker-compose down

Result:

Stopping my-app_web_1 ... done
Stopping my-app_db_1  ... done
Removing my-app_web_1 ... done
Removing my-app_db_1  ... done
Removing network my-app_app-network

(Volumes are not removed by default unless you use docker-compose down -v)

3. Key Compose Features

  • Project Names: Docker prefixes network/container names with your folder name (e.g., my-app_).
  • Dependency Management: depends_on ensures services start in order.
  • Scaling: You can scale a service using docker-compose up --scale web=3.

Summary

  • One file defines your entire application stack.
  • up: Starts everything.
  • down: Stops and removes everything.
  • Environment variables, volumes, and networks are all defined in the YAML.