Docker Compose Secure Generator

Generate Docker Compose configurations with security hardening by default.

Security Principles

This skill enforces security best practices that prevent common attack vectors:

1. Port Binding - CRITICAL

ALWAYS bind ports to localhost (127.0.0.1) by default.

# ✅ CORRECT - Secure by default
ports:
  - "127.0.0.1:8080:8080"
  - "127.0.0.1:5432:5432"

# ❌ NEVER DO THIS - Exposes to entire internet
ports:
  - "8080:8080"        # Binds to 0.0.0.0!
  - "5432:5432"        # Database exposed publicly!

Why this matters: A port binding like "3000:3000" exposes the service to the entire internet (0.0.0.0). Attackers actively scan for exposed development servers, databases, and admin panels. This exact vulnerability led to server compromise with cryptominer malware.

Only use 0.0.0.0 when:

• The service is explicitly designed for public access
• A reverse proxy (nginx, traefik) handles TLS termination
• Firewall rules restrict access appropriately
• The user explicitly requests public exposure

2. Security Options - REQUIRED

ALWAYS include security_opt in every service:

services:
  app:
    security_opt:
      - no-new-privileges:true

Why: Prevents privilege escalation attacks. A compromised process cannot gain additional privileges.

3. User Configuration - RECOMMENDED

Run as non-root when possible:

services:
  app:
    user: "1000:1000"
    # OR use the built-in node user for Node.js images
    user: "node"

4. Read-Only Filesystem - WHEN APPLICABLE

services:
  app:
    read_only: true
    tmpfs:
      - /tmp
      - /var/run

5. Resource Limits - RECOMMENDED

Prevent resource exhaustion attacks:

services:
  app:
    deploy:
      resources:
        limits:
          cpus: '2.0'
          memory: 512M
        reservations:
          cpus: '0.5'
          memory: 128M

6. Network Isolation

Create isolated networks, don't use default bridge:

networks:
  backend:
    driver: bridge
    internal: true  # No external access
  frontend:
    driver: bridge

services:
  db:
    networks:
      - backend  # Only accessible from backend network

  app:
    networks:
      - backend
      - frontend

7. Health Checks - REQUIRED

services:
  app:
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost:8080/health"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s

8. Environment Variables - SECURE HANDLING

NEVER hardcode secrets in docker-compose.yml:

# ✅ CORRECT - Use environment files
services:
  app:
    env_file:
      - .env  # Git-ignored file with secrets

# ✅ CORRECT - Use Docker secrets (Swarm mode)
services:
  app:
    secrets:
      - db_password

secrets:
  db_password:
    external: true

# ❌ NEVER - Hardcoded secrets
services:
  app:
    environment:
      - DB_PASSWORD=supersecret123  # Will be in git history!

9. Logging Configuration

Prevent log file exhaustion:

services:
  app:
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "3"

10. No Privileged Mode

NEVER use privileged mode unless absolutely necessary:

# ❌ AVOID - Full host access
services:
  app:
    privileged: true  # DANGEROUS!

# ✅ PREFER - Specific capabilities only
services:
  app:
    cap_add:
      - NET_ADMIN  # Only if needed
    cap_drop:
      - ALL  # Drop all capabilities first

Complete Secure Template

services:
  app:
    image: myapp:latest
    container_name: myapp
    restart: unless-stopped
    user: "1000:1000"
    read_only: true
    security_opt:
      - no-new-privileges:true
    cap_drop:
      - ALL
    ports:
      - "127.0.0.1:8080:8080"
    networks:
      - app-network
    volumes:
      - app-data:/app/data:rw
    tmpfs:
      - /tmp
      - /var/run
    env_file:
      - .env
    healthcheck:
      test: ["CMD", "wget", "--spider", "-q", "http://localhost:8080/health"]
      interval: 30s
      timeout: 10s
      retries: 3
      start_period: 40s
    deploy:
      resources:
        limits:
          cpus: '2.0'
          memory: 512M
        reservations:
          cpus: '0.25'
          memory: 128M
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "3"

networks:
  app-network:
    driver: bridge

volumes:
  app-data:

Common Service Templates

PostgreSQL (Secure)

services:
  postgres:
    image: postgres:16-alpine
    container_name: postgres
    restart: unless-stopped
    security_opt:
      - no-new-privileges:true
    ports:
      - "127.0.0.1:5432:5432"
    environment:
      POSTGRES_DB: ${POSTGRES_DB}
      POSTGRES_USER: ${POSTGRES_USER}
      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
    volumes:
      - postgres-data:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
      interval: 10s
      timeout: 5s
      retries: 5
    networks:
      - backend
    deploy:
      resources:
        limits:
          cpus: '2.0'
          memory: 1G

volumes:
  postgres-data:

networks:
  backend:
    internal: true

Redis (Secure)

services:
  redis:
    image: redis:7-alpine
    container_name: redis
    restart: unless-stopped
    security_opt:
      - no-new-privileges:true
    command: redis-server --requirepass ${REDIS_PASSWORD} --appendonly yes
    ports:
      - "127.0.0.1:6379:6379"
    volumes:
      - redis-data:/data
    healthcheck:
      test: ["CMD", "redis-cli", "-a", "${REDIS_PASSWORD}", "ping"]
      interval: 10s
      timeout: 5s
      retries: 5
    networks:
      - backend
    deploy:
      resources:
        limits:
          cpus: '1.0'
          memory: 256M

volumes:
  redis-data:

networks:
  backend:
    internal: true

Node.js Application (Secure)

services:
  node-app:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: node-app
    restart: unless-stopped
    user: "node"
    read_only: true
    security_opt:
      - no-new-privileges:true
    cap_drop:
      - ALL
    ports:
      - "127.0.0.1:3000:3000"
    tmpfs:
      - /tmp
    env_file:
      - .env
    healthcheck:
      test: ["CMD", "node", "-e", "require('http').get('http://localhost:3000/health', (r) => process.exit(r.statusCode === 200 ? 0 : 1))"]
      interval: 30s
      timeout: 10s
      retries: 3
    networks:
      - app-network
    depends_on:
      postgres:
        condition: service_healthy
      redis:
        condition: service_healthy
    deploy:
      resources:
        limits:
          cpus: '2.0'
          memory: 512M

networks:
  app-network:
    driver: bridge

Nginx Reverse Proxy (Secure)

services:
  nginx:
    image: nginx:alpine
    container_name: nginx
    restart: unless-stopped
    security_opt:
      - no-new-privileges:true
    cap_drop:
      - ALL
    cap_add:
      - NET_BIND_SERVICE
    ports:
      # Only nginx should be publicly accessible
      - "0.0.0.0:80:80"
      - "0.0.0.0:443:443"
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
      - ./ssl:/etc/nginx/ssl:ro
    healthcheck:
      test: ["CMD", "nginx", "-t"]
      interval: 30s
      timeout: 10s
      retries: 3
    networks:
      - frontend
      - backend
    depends_on:
      - app
    deploy:
      resources:
        limits:
          cpus: '1.0'
          memory: 128M

networks:
  frontend:
    driver: bridge
  backend:
    internal: true

Validation Checklist

Before generating any Docker Compose file, verify:

• All ports use 127.0.0.1: prefix (unless explicitly public-facing like nginx)
• security_opt: [no-new-privileges:true] is present
• No hardcoded passwords or secrets
• restart: unless-stopped for production services
• Health checks defined for all services
• Resource limits defined
• Logging limits configured
• No privileged: true unless absolutely necessary
• Sensitive services on internal networks

Warning About Public Exposure

If a user explicitly requests public port exposure, include this warning:

# ⚠️ WARNING: This port is publicly accessible (0.0.0.0)
# Ensure you have:
# - Firewall rules configured (UFW, iptables)
# - TLS/HTTPS enabled
# - Authentication required
# - Rate limiting in place
ports:
  - "0.0.0.0:443:443"  # INTENTIONALLY PUBLIC

References

• Docker Security Best Practices
• CIS Docker Benchmark
• OWASP Docker Security Cheat Sheet