Docker Compose in Practice — Configuring Multi-Container Apps

services:
  app:
    build: .
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
    depends_on:
      db:
        condition: service_healthy
    volumes:
      - ./logs:/app/logs

  db:
    image: postgres:16-alpine
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: user
      POSTGRES_PASSWORD: secret
    volumes:
      - pg_data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user -d mydb"]
      interval: 10s
      timeout: 5s
      retries: 5

volumes:
  pg_data:

# Build + start (detached)
docker compose up -d --build

# Restart a specific service only
docker compose restart app

# Follow logs in real time
docker compose logs -f app

# Status of running containers
docker compose ps

# Shell into a container
docker compose exec app sh

# Stop everything + remove networks/volumes
docker compose down -v

# Scale up (run 3 instances of the app service)
docker compose up -d --scale app=3

# .env file (loaded automatically by default)
DB_PASSWORD=secret
APP_PORT=3000

# Used in docker-compose.yml
environment:
  DB_PASSWORD: ${DB_PASSWORD}
  APP_PORT: ${APP_PORT}

# Environment-specific override
docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d

services:
  app:
    image: myapp:latest
    deploy:
      resources:
        limits:
          cpus: "0.50"
          memory: 512M
        reservations:
          cpus: "0.25"
          memory: 256M

services:
  nginx:
    image: nginx:alpine
    ports:
      - "80:80"
      - "443:443"
    volumes:
      - ./nginx/conf.d:/etc/nginx/conf.d:ro
      - ./certbot/conf:/etc/letsencrypt:ro
    depends_on:
      - app

  app:
    build:
      context: .
      dockerfile: Dockerfile
    expose:
      - "3000"
    env_file:
      - .env
    depends_on:
      db:
        condition: service_healthy
    restart: unless-stopped

  db:
    image: postgres:16-alpine
    volumes:
      - pg_data:/var/lib/postgresql/data
      - ./sql/init.sql:/docker-entrypoint-initdb.d/init.sql
    env_file:
      - .env.db
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER}"]
      interval: 10s
      retries: 5
    restart: unless-stopped

volumes:
  pg_data: