What is Docker Compose?

#What is Docker Compose?

After this lesson you'll know:

• why you need docker compose
• how a docker-compose.yml is structured
• the most important compose commands

#The problem with docker run

Your app needs a database. Maybe Redis. A message broker.

Sure, you could type three docker run commands. Every time. In the right order. With the right networks.

Or you define everything in one file.

#docker-compose.yml

services:
  web:
    image: nginx
    ports:
      - "8080:80"
  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_PASSWORD: secret
      POSTGRES_DB: myapp

docker compose up -d   # Start everything
docker compose down    # Stop everything

#Key Concepts

• Services = your containers
• Networks = how services communicate (automatically created!)
• Volumes = persistent data
• Environment = environment variables

Services in the same Compose file are automatically on the same network. You reach db simply as db (hostname = service name).

#Important Commands

docker compose up -d       # Start
docker compose down        # Stop + remove network
docker compose ps          # Status
docker compose logs -f     # Follow logs
docker compose exec web sh # Shell into container
docker compose build       # Build images (when using build: .)

#✋ Try it out

• Create a docker-compose.yml with a web service (nginx) and start it with docker compose up -d. Open http://localhost:80
• Add a db service (postgres), restart, check with docker compose ps
• docker compose logs -f — follow the logs of both services

#📌 Summary

• docker compose defines all services in one YAML file
• One command starts/stops everything
• Services automatically find each other by name