Docker Compose Files: The YAML Configuration That Replaces 20 Pages of Setup Documentation

Every project has a setup document. "Install Postgres 15. Create a database called app_dev. Install Redis. Set the REDIS_URL environment variable. Install Node 20. Run npm install. Start the server." Docker Compose replaces all of that with a single file that anyone can run with one command. I converted my team's 4-page setup document into a docker-compose.yml file that takes 30 seconds to start. Here is what I learned about getting it right. The structure of a compose file A docker-compose.yml defines services (containers), their configuration, and how they connect: version: '3.8' services: app: build: . ports: - "3000:3000" environment: - DATABASE_URL=postgres://user:pass@db:5432/app - REDIS_URL=redis://cache:6379 depends_on: - db - cache db: image: postgres:15 environment: - POSTGRES_USER=user - POSTGRES_PASSWORD=pass - POSTGRES_DB=app volumes: - pgdata:/var/lib/postgresql/data cache: image: redis:7-alpine ports: - "6379:6379" volumes: pgdata: docker compose up starts all three serv