Docker Compose Generator

Docker Compose Configuration Generator

This skill focuses on containerizing applications effectively, prioritizing security, multi-stage builds, performance, and best practices for Docker Compose files.

Guidelines

When creating Docker environments, follow these rules:

1. Multi-Stage Builds: Use multi-stage Dockerfiles to separate build environments from runtime environments. This reduces the final image size significantly.
2. Minimal Base Images: Prefer alpine, distroless, or slim tags for base images to minimize vulnerabilities.
3. Non-Root User: Never run the application as root inside the container unless strictly necessary. Switch to a less privileged user.
4. Environment Variables: Use .env files and environment properties in docker-compose.yml to inject configuration at runtime.
5. Caching: Optimize COPY and RUN instructions to leverage Docker's build cache effectively (e.g., copy package.json before copying the rest of the source code).
6. Volumes: Use named volumes for persistent data (databases) and bind mounts for local development (hot-reloading).
7. Networking: Ensure services are attached to custom networks to control communication securely. Use depends_on and health checks to ensure proper startup sequencing.

Template

Provide responses in this structure:

1. Dockerfile

Provide a robust multi-stage Dockerfile for the primary application (e.g., Node.js, Go, Python). Include comments explaining the stages.

# Stage 1: Build environment
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Production environment
FROM node:18-alpine AS runner
WORKDIR /app
# Run as non-root user
USER node
COPY --from=builder --chown=node:node /app/dist ./dist
COPY --from=builder --chown=node:node /app/node_modules ./node_modules
COPY --from=builder --chown=node:node /app/package.json ./package.json

# Expose port and start
EXPOSE 3000
CMD ["npm", "start"]

2. docker-compose.yml

Provide the complete Compose file defining the services, networks, and volumes.

version: '3.8'

services:
  web:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    environment:
      - NODE_ENV=production
      - DB_HOST=db
      - DB_USER=${DB_USER}
      - DB_PASSWORD=${DB_PASSWORD}
    depends_on:
      db:
        condition: service_healthy
    networks:
      - app-network

  db:
    image: postgres:15-alpine
    environment:
      - POSTGRES_USER=${DB_USER}
      - POSTGRES_PASSWORD=${DB_PASSWORD}
      - POSTGRES_DB=myapp
    volumes:
      - postgres_data:/var/lib/postgresql/data
    networks:
      - app-network
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U ${DB_USER} -d myapp"]
      interval: 10s
      timeout: 5s
      retries: 5

networks:
  app-network:
    driver: bridge

volumes:
  postgres_data:

3. Usage Instructions

Include instructions on how to start the environment:

• Create .env file containing variables (provide an example .env.example).
• Run docker-compose up -d --build.