Running one container is useful. Real projects often need an API plus a database, cache, or worker. Docker Compose lets you describe and start that local stack from one YAML file.

Why Compose exists

Real backend apps often need more than one service.

Examples:

• API.
• Database.
• Redis.
• Queue worker.
• Admin UI.

Compose starts these together for local development and simple environments.

Example

services:
  api:
    build: .
    ports:
      - "3000:3000"
    environment:
      DATABASE_URL: postgres://postgres:postgres@db:5432/app
    depends_on:
      - db

  db:
    image: postgres:16
    environment:
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: app
    volumes:
      - db-data:/var/lib/postgresql/data

volumes:
  db-data:

The API connects to host db because db is the Compose service name.

Common commands

docker compose up
docker compose up -d
docker compose down
docker compose logs -f
docker compose exec api sh

up starts services. down stops and removes containers created by the Compose project.

depends_on

depends_on controls startup order, but it does not guarantee the database is ready for queries.

Applications should still handle retries or wait for readiness.

Environment files

Compose can load variables from .env, but be careful not to commit real secrets.

Use example files like .env.example for documentation.

Quick revision

• Compose defines multiple services in YAML.
• Services can communicate by service name.
• Volumes preserve service data.
• depends_on is startup order, not readiness.
• Compose is excellent for local development.