Docker Compose

Master Docker Compose for defining and running multi-container applications, covering service configuration, networking, volumes, and production deployment patterns.

Docker Compose is a tool for defining and running multi-container Docker applications. Using a YAML file, you configure all your application's services, networks, and volumes, then create and start everything with a single command.

Docker Compose Architecture

│ docker-compose.yml defines	│
│ │ │	80 │──│ :3000 │──│ :5432 │ │ │
│ │ Port 80	80 ┌────┴────┐ │ │

Complete Docker Compose Example

Example

# docker-compose.yml - Full-stack web application version: '3.9' services: # Frontend (React app served by Nginx) frontend: build: context: ./frontend dockerfile: Dockerfile ports: - "80:80" depends_on: - api networks: - app-network restart: unless-stopped # Backend API (Node.js) api: build: context: ./backend dockerfile: Dockerfile ports: - "3000:3000" environment: - NODE_ENV=production - DATABASE_URL=postgresql://app_user:secret@db:5432/appdb - REDIS_URL=redis://cache:6379 depends_on: db: condition: service_healthy cache: condition: service_started networks: - app-network restart: unless-stopped deploy: resources: limits: memory: 512M cpus: '1.0' # Database (PostgreSQL) db: image: postgres:15-alpine environment: POSTGRES_DB: appdb POSTGRES_USER: app_user POSTGRES_PASSWORD: secret volumes: - db-data:/var/lib/postgresql/data - ./init.sql:/docker-entrypoint-initdb.d/init.sql ports: - "5432:5432" networks: - app-network healthcheck: test: ["CMD-SHELL", "pg_isready -U app_user -d appdb"] interval: 10s timeout: 5s retries: 5 restart: unless-stopped # Cache (Redis) cache: image: redis:7-alpine ports: - "6379:6379" volumes: - cache-data:/data networks: - app-network command: redis-server --maxmemory 256mb --maxmemory-policy allkeys-lru restart: unless-stopped # Background Worker worker: build: context: ./backend dockerfile: Dockerfile command: node worker.js environment: - DATABASE_URL=postgresql://app_user:secret@db:5432/appdb - REDIS_URL=redis://cache:6379 depends_on: - db - cache networks: - app-network restart: unless-stopped networks: app-network: driver: bridge volumes: db-data: cache-data:

Docker Compose Commands

bash example

# Start all services
docker compose up -d

# Start with build
docker compose up -d --build

# View running services
docker compose ps

# View logs
docker compose logs -f
docker compose logs -f api  # Single service

# Stop all services
docker compose down

# Stop and remove volumes (clean slate)
docker compose down -v

# Scale a service
docker compose up -d --scale api=3

# Execute command in a service
docker compose exec api npm run migrate

# Restart a single service
docker compose restart api

# View resource usage
docker compose top

Environment Variables and Secrets

yaml example

# docker-compose.yml with .env file
services:
  api:
    image: my-api:${APP_VERSION:-latest}
    env_file:
      - .env
      - .env.production
    environment:
      - API_KEY=${API_KEY}
    secrets:
      - db_password

secrets:
  db_password:
    file: ./secrets/db_password.txt

Example

# .env file APP_VERSION=2.1.0 POSTGRES_PASSWORD=[REDACTED_PASSWORD] API_KEY=your-api-key-here

Development vs Production Compose

yaml example

# docker-compose.override.yml (dev - auto-loaded)
services:
  api:
    build:
      context: ./backend
    volumes:
      - ./backend:/app  # Live code reload
      - /app/node_modules
    environment:
      - NODE_ENV=development
      - DEBUG=true
    command: npm run dev

bash example

# Production deployment
docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d

Health Checks and Dependencies

Example

services: api: depends_on: db: condition: service_healthy cache: condition: service_healthy healthcheck: test: ["CMD", "curl", "-f", "http://localhost:3000/health"] interval: 30s timeout: 10s retries: 3 start_period: 40s

Interview Questions

What is Docker Compose and when would you use it?

Docker Compose defines multi-container applications in a YAML file. Use it when your application has multiple services (web server, API, database, cache) that need to work together. It simplifies local development and can be used for single-host production deployments.

Explain the difference between depends_on and health checks.

depends_on only waits for a container to start (process running). Health checks verify the service is actually ready (database accepting connections). Combine them with condition: service_healthy to ensure dependent services wait for true readiness.

How do you manage secrets in Docker Compose?

Use Docker secrets (file-based), environment variables from .env files (not committed to git), or external secret managers. Never hardcode secrets in docker-compose.yml. For production, use Docker Swarm secrets or external tools like Vault.

How would you set up a development environment with Docker Compose?

Use bind mounts for live code reload, docker-compose.override.yml for dev-specific settings, development commands (hot reload), exposed debug ports, and lighter resource constraints. This gives the full production stack locally with developer ergonomics.

What are the limitations of Docker Compose for production?

Single-host only (no clustering), limited health management, no rolling updates natively, no load balancing across hosts. For production at scale, use Kubernetes, Docker Swarm, or ECS. Compose is ideal for development, testing, and small single-server deployments.

Docker Compose Architecture

│ docker-compose.yml defines	│
│ │ │	80 │──│ :3000 │──│ :5432 │ │ │
│ │ Port 80	80 ┌────┴────┐ │ │

Complete Docker Compose Example

Example

Docker Compose Commands

bash example

# Start all services
docker compose up -d

# Start with build
docker compose up -d --build

# View running services
docker compose ps

# View logs
docker compose logs -f
docker compose logs -f api  # Single service

# Stop all services
docker compose down

# Stop and remove volumes (clean slate)
docker compose down -v

# Scale a service
docker compose up -d --scale api=3

# Execute command in a service
docker compose exec api npm run migrate

# Restart a single service
docker compose restart api

# View resource usage
docker compose top

Environment Variables and Secrets

yaml example

# docker-compose.yml with .env file
services:
  api:
    image: my-api:${APP_VERSION:-latest}
    env_file:
      - .env
      - .env.production
    environment:
      - API_KEY=${API_KEY}
    secrets:
      - db_password

secrets:
  db_password:
    file: ./secrets/db_password.txt

Example

# .env file APP_VERSION=2.1.0 POSTGRES_PASSWORD=[REDACTED_PASSWORD] API_KEY=your-api-key-here

Development vs Production Compose

yaml example

# docker-compose.override.yml (dev - auto-loaded)
services:
  api:
    build:
      context: ./backend
    volumes:
      - ./backend:/app  # Live code reload
      - /app/node_modules
    environment:
      - NODE_ENV=development
      - DEBUG=true
    command: npm run dev

bash example

# Production deployment
docker compose -f docker-compose.yml -f docker-compose.prod.yml up -d

Health Checks and Dependencies

Example

Interview Questions

What is Docker Compose and when would you use it?

Explain the difference between depends_on and health checks.

How do you manage secrets in Docker Compose?

How would you set up a development environment with Docker Compose?

What are the limitations of Docker Compose for production?

Docker Compose

Docker Compose Architecture

Complete Docker Compose Example

Docker Compose Commands

Environment Variables and Secrets

Development vs Production Compose

Health Checks and Dependencies

Interview Questions

Continue learning this concept

Docker Compose

Docker Compose Architecture

Complete Docker Compose Example

Docker Compose Commands

Environment Variables and Secrets

Development vs Production Compose

Health Checks and Dependencies

Interview Questions

Continue learning this concept