Web + Postgres + Redis

services:
  web:
    build: .
    ports:
      - "8080:3000"
    environment:
      # "db" and "cache" resolve via Compose's built-in DNS -- no need to
      # know the containers' actual IPs, which change on every recreate.
      DATABASE_URL: postgres://app:app@db:5432/app
      REDIS_URL: redis://cache:6379
    depends_on:
      db:
        # Waits for Postgres to report healthy, not just for the
        # container to start -- avoids a race against db init time.
        condition: service_healthy
      cache:
        condition: service_started
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_USER: app
      POSTGRES_PASSWORD: app
      POSTGRES_DB: app
    volumes:
      # Named volume so data survives "docker compose down" (but not
      # "docker compose down -v").
      - db-data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U app"]
      interval: 5s
      timeout: 3s
      retries: 5

  cache:
    image: redis:7-alpine

volumes:
  db-data: