마이크로서비스

// 마이크로서비스 예제 - 사용자 서비스 (Express + TypeScript)
import express, { Request, Response } from 'express';
import axios from 'axios';

const app = express();
app.use(express.json());

// 서비스 디스커버리 (Consul, Eureka 등 사용 가능)
const SERVICE_REGISTRY = {
    'order-service': process.env.ORDER_SERVICE_URL || 'http://order-service:3000',
    'notification-service': process.env.NOTIFICATION_SERVICE_URL || 'http://notification-service:3000'
};

interface User {
    id: string;
    name: string;
    email: string;
    createdAt: Date;
}

// 인메모리 저장소 (실제로는 독립 DB 사용)
const usersDb = new Map();

// Circuit Breaker 패턴 구현
class CircuitBreaker {
    private failures = 0;
    private lastFailureTime = 0;
    private readonly threshold = 5;
    private readonly timeout = 30000; // 30초

    async call(fn: () => Promise): Promise {
        if (this.isOpen()) {
            throw new Error('Circuit breaker is open');
        }

        try {
            const result = await fn();
            this.reset();
            return result;
        } catch (error) {
            this.recordFailure();
            throw error;
        }
    }

    private isOpen(): boolean {
        if (this.failures >= this.threshold) {
            const timeSinceLastFailure = Date.now() - this.lastFailureTime;
            return timeSinceLastFailure < this.timeout;
        }
        return false;
    }

    private recordFailure(): void {
        this.failures++;
        this.lastFailureTime = Date.now();
    }

    private reset(): void {
        this.failures = 0;
    }
}

const notificationBreaker = new CircuitBreaker();

// 사용자 생성
app.post('/users', async (req: Request, res: Response) => {
    const { name, email } = req.body;

    const user: User = {
        id: `USER-${Date.now()}`,
        name,
        email,
        createdAt: new Date()
    };

    usersDb.set(user.id, user);

    // 알림 서비스에 이벤트 발행 (비동기, 실패해도 사용자 생성은 성공)
    try {
        await notificationBreaker.call(async () => {
            await axios.post(
                `${SERVICE_REGISTRY['notification-service']}/notifications`,
                {
                    type: 'USER_CREATED',
                    userId: user.id,
                    email: user.email,
                    message: '회원가입을 환영합니다!'
                }
            );
        });
    } catch (error) {
        console.error('알림 서비스 호출 실패 (무시됨):', error);
        // 알림 실패는 사용자 생성 실패로 이어지지 않음
    }

    res.status(201).json(user);
});

// 사용자 조회
app.get('/users/:id', (req: Request, res: Response) => {
    const user = usersDb.get(req.params.id);

    if (!user) {
        return res.status(404).json({ error: '사용자를 찾을 수 없습니다' });
    }

    res.json(user);
});

// 헬스 체크
app.get('/health', (req: Request, res: Response) => {
    res.json({
        status: 'healthy',
        service: 'user-service',
        timestamp: new Date().toISOString()
    });
});

// 메트릭 엔드포인트 (Prometheus 수집용)
app.get('/metrics', (req: Request, res: Response) => {
    res.set('Content-Type', 'text/plain');
    res.send(`
# HELP users_total Total number of users
# TYPE users_total counter
users_total ${usersDb.size}
    `);
});

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => {
    console.log(`User service running on port ${PORT}`);
});

# 마이크로서비스 아키텍처 구조 (Kubernetes + Docker Compose)

# ========================================
# docker-compose.yml - 로컬 개발 환경
# ========================================
version: '3.8'

services:
  # API Gateway - 모든 요청의 진입점
  api-gateway:
    image: nginx:alpine
    ports:
      - "80:80"
    depends_on:
      - user-service
      - order-service
      - product-service
    networks:
      - microservices-network

  # 사용자 서비스
  user-service:
    build: ./services/user
    environment:
      - DATABASE_URL=postgres://user-db:5432/users
      - NOTIFICATION_SERVICE_URL=http://notification-service:3000
    depends_on:
      - user-db
    networks:
      - microservices-network

  # 주문 서비스
  order-service:
    build: ./services/order
    environment:
      - DATABASE_URL=postgres://order-db:5432/orders
      - USER_SERVICE_URL=http://user-service:8000
      - PRODUCT_SERVICE_URL=http://product-service:8000
      - KAFKA_BROKERS=kafka:9092
    depends_on:
      - order-db
      - kafka
    networks:
      - microservices-network

  # 상품 서비스
  product-service:
    build: ./services/product
    environment:
      - DATABASE_URL=mongo://product-db:27017/products
    depends_on:
      - product-db
    networks:
      - microservices-network

  # 각 서비스별 독립 데이터베이스
  user-db:
    image: postgres:15
    environment:
      POSTGRES_DB: users
    volumes:
      - user-data:/var/lib/postgresql/data
    networks:
      - microservices-network

  order-db:
    image: postgres:15
    environment:
      POSTGRES_DB: orders
    networks:
      - microservices-network

  product-db:
    image: mongo:6
    networks:
      - microservices-network

  # 메시지 브로커 (비동기 통신)
  kafka:
    image: confluentinc/cp-kafka:latest
    environment:
      KAFKA_ZOOKEEPER_CONNECT: zookeeper:2181
    depends_on:
      - zookeeper
    networks:
      - microservices-network

  zookeeper:
    image: confluentinc/cp-zookeeper:latest
    networks:
      - microservices-network

networks:
  microservices-network:
    driver: bridge

volumes:
  user-data:

# ========================================
# 프로젝트 디렉토리 구조
# ========================================
# microservices-app/
# ├── docker-compose.yml
# ├── k8s/
# │   ├── user-service.yaml
# │   ├── order-service.yaml
# │   └── api-gateway.yaml
# ├── services/
# │   ├── user/
# │   │   ├── Dockerfile
# │   │   ├── package.json
# │   │   └── src/
# │   ├── order/
# │   │   ├── Dockerfile
# │   │   ├── requirements.txt
# │   │   └── app/
# │   └── product/
# │       ├── Dockerfile
# │       └── src/
# └── shared/
#     ├── proto/           # gRPC 프로토콜 정의
#     └── events/          # 공유 이벤트 스키마