[Spring Cloud] Eureka, Config, Gateway, OpenFeign

2026년 6월 20일 · 수정 2026년 6월 20일 · 📖 약 2분 · 587자/단어 #spring #spring-cloud #microservices

정의

Spring Cloud는 Spring Boot 기반 마이크로서비스 인프라 패턴 (service discovery, config server, gateway, circuit breaker, distributed tracing 등)을 제공한다. Netflix OSS와의 호흡, 현재는 Resilience4j, Micrometer Tracing 등 Spring 자체 / open source 대안 위주.

핵심 컴포넌트

컴포넌트	역할
Spring Cloud Config	중앙 설정 서버
Eureka / Consul / Nacos	Service Discovery
Spring Cloud Gateway	API Gateway (라우팅, 필터)
OpenFeign	선언형 HTTP 클라이언트
Spring Cloud LoadBalancer	클라이언트 로드밸런싱
Resilience4j	Circuit Breaker, Retry, Rate Limit
Micrometer Tracing	분산 트레이싱 (OpenTelemetry)
Spring Cloud Stream	메시지 추상화 (Kafka, RabbitMQ)
Spring Cloud Sleuth	(Deprecated → Micrometer Tracing)

Service Discovery (Eureka)

Eureka Server

implementation("org.springframework.cloud:spring-cloud-starter-netflix-eureka-server")

@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }
}

server:
  port: 8761
eureka:
  client:
    register-with-eureka: false    # 서버 자신은 등록 X
    fetch-registry: false

Eureka Client

implementation("org.springframework.cloud:spring-cloud-starter-netflix-eureka-client")

spring:
  application:
    name: user-service
eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/

서비스가 시작 시 Eureka에 자동 등록. 다른 서비스가 이름으로 찾음.

대안

Consul (HashiCorp): 더 일반적
Nacos (Alibaba): 설정 + 등록 통합
etcd, ZooKeeper: 저수준
Kubernetes Service Discovery: k8s 환경엔 가장 자연스러움

Spring Cloud Config

중앙 설정 서버. 모든 서비스가 시작 시 설정을 fetch.

Config Server

implementation("org.springframework.cloud:spring-cloud-config-server")

@SpringBootApplication
@EnableConfigServer
public class ConfigServerApplication { ... }

server:
  port: 8888
spring:
  cloud:
    config:
      server:
        git:
          uri: https://github.com/org/config-repo

Git 리포지토리에 {서비스명}-{프로파일}.yml 파일.

Config Client

implementation("org.springframework.cloud:spring-cloud-starter-config")

# bootstrap.yml (또는 application.yml 3.4+)
spring:
  application:
    name: user-service
  config:
    import: optional:configserver:http://localhost:8888

config-repo/user-service-prod.yml이 자동 로드.

@Value("${db.url}")
private String dbUrl;

@RefreshScope    // POST /actuator/refresh로 재로드
public class MyBean { ... }

대안

Kubernetes ConfigMap + Secret
AWS Parameter Store / Secrets Manager
HashiCorp Vault

Spring Cloud Gateway

설정

implementation("org.springframework.cloud:spring-cloud-starter-gateway")

WebFlux 기반이라 web starter와 충돌.

spring:
  cloud:
    gateway:
      routes:
        - id: user-service
          uri: lb://user-service    # Eureka에서 lookup
          predicates:
            - Path=/api/users/**
          filters:
            - RewritePath=/api/(?<segment>.*), /$\{segment}
            - AddRequestHeader=X-Gateway, true
        - id: order-service
          uri: lb://order-service
          predicates:
            - Path=/api/orders/**
            - Method=GET,POST

lb:// = 로드밸런서 (Eureka 통합).

Filter

@Component
public class AuthFilter extends AbstractGatewayFilterFactory<AuthFilter.Config> {

    @Override
    public GatewayFilter apply(Config config) {
        return (exchange, chain) -> {
            String token = exchange.getRequest().getHeaders().getFirst("Authorization");
            if (token == null || !isValid(token)) {
                exchange.getResponse().setStatusCode(HttpStatus.UNAUTHORIZED);
                return exchange.getResponse().setComplete();
            }
            return chain.filter(exchange);
        };
    }

    public static class Config { }
}

OpenFeign (선언형 HTTP)

implementation("org.springframework.cloud:spring-cloud-starter-openfeign")

@SpringBootApplication
@EnableFeignClients
public class App { }

@FeignClient(name = "user-service")    // Eureka name
public interface UserClient {

    @GetMapping("/users/{id}")
    User findById(@PathVariable Long id);

    @PostMapping("/users")
    User create(@RequestBody CreateUserDto dto);

    @GetMapping("/users")
    List<User> search(@RequestParam String q);
}

@Service
public class OrderService {
    private final UserClient userClient;

    public Order createOrder(...) {
        User user = userClient.findById(userId);    // 자동 HTTP 호출
        ...
    }
}

선언만으로 HTTP 클라이언트. Eureka, LoadBalancer, Circuit Breaker 자동 통합.

Fallback

@FeignClient(name = "user-service", fallback = UserClientFallback.class)
public interface UserClient { ... }

@Component
public class UserClientFallback implements UserClient {
    @Override
    public User findById(Long id) {
        return User.empty();    // 빈 객체 또는 에러 마킹
    }
}

Resilience4j

Circuit Breaker

implementation("org.springframework.cloud:spring-cloud-starter-circuitbreaker-reactor-resilience4j")

@Service
public class UserService {
    private final UserClient userClient;
    private final CircuitBreakerFactory cbFactory;

    public User getUser(Long id) {
        return cbFactory.create("user-service")
            .run(
                () -> userClient.findById(id),
                throwable -> User.empty()    // fallback
            );
    }
}

resilience4j:
  circuitbreaker:
    instances:
      user-service:
        failure-rate-threshold: 50
        wait-duration-in-open-state: 30s
        sliding-window-size: 10

Retry

@Retry(name = "user-service", fallbackMethod = "fallback")
public User getUser(Long id) {
    return userClient.findById(id);
}

public User fallback(Long id, Exception ex) {
    return User.empty();
}

Rate Limit, Bulkhead

설정으로 정의 + 어노테이션 적용.

Distributed Tracing

implementation("io.micrometer:micrometer-tracing-bridge-otel")
implementation("io.opentelemetry:opentelemetry-exporter-otlp")

management:
  tracing:
    sampling:
      probability: 1.0
otel:
  exporter:
    otlp:
      endpoint: http://otel-collector:4317

OpenTelemetry로 모든 요청에 trace ID 부여. Jaeger, Zipkin, Datadog, Honeycomb 등에서 분산 트랜잭션 추적.

Spring Cloud Stream

implementation("org.springframework.cloud:spring-cloud-stream")
implementation("org.springframework.cloud:spring-cloud-stream-binder-kafka")

@Bean
public Consumer<OrderCreatedEvent> processOrder() {
    return event -> {
        log.info("Order created: {}", event);
        ...
    };
}

@Bean
public Supplier<String> heartbeat() {
    return () -> "ping " + Instant.now();
}

spring:
  cloud:
    stream:
      bindings:
        processOrder-in-0:
          destination: orders
          group: order-processors
        heartbeat-out-0:
          destination: heartbeats
      kafka:
        binder:
          brokers: localhost:9092

Kafka, RabbitMQ 통일 인터페이스.

자주 보는 패턴

Microservice + Gateway 구조

[Client]
   ↓
[Gateway] (8080)
   ├→ user-service (Eureka lookup)
   ├→ order-service
   └→ product-service
       ↓ OpenFeign
       ↓
   user-service (조회)

Saga pattern

분산 트랜잭션. Spring Cloud Stream + Kafka로 이벤트 기반 보상.

// OrderService
@Transactional
public void createOrder(...) {
    Order order = orderRepository.save(...);
    eventPublisher.publishEvent(new OrderCreatedEvent(order.getId()));
}

// PaymentService listens
@Bean
public Consumer<OrderCreatedEvent> processPayment() {
    return event -> {
        try {
            charge(event.orderId());
            publish(new PaymentSucceededEvent(...));
        } catch (Exception e) {
            publish(new PaymentFailedEvent(...));    // 보상
        }
    };
}

함정

1. Spring Cloud 버전 호환성

Spring Boot 3.4 ↔ Spring Cloud 2024.0.x. release train 매트릭스 확인.

2. bootstrap.yml deprecated

# 3.4+
spring:
  config:
    import: configserver:http://localhost:8888

bootstrap.yml 대신 spring.config.import.

3. Eureka heartbeat

서비스가 정기 heartbeat 안 보내면 30초 후 제외. 네트워크 이슈 시 false negative 가능.

4. Gateway WebFlux

Gateway는 reactive. blocking call 금지. 모든 downstream도 reactive 또는 별 스레드.

5. config 중앙화의 위험

Config Server 다운 → 모든 서비스 시작 실패. fallback 또는 cache (Spring Cloud Config가 last-known 보존).

Kubernetes-native 대안

K8s 환경이면 Spring Cloud 대안:

Service Discovery: K8s Service / DNS
Config: ConfigMap, Secret
Gateway: Istio, Linkerd, Kong
Circuit Breaker: Istio
Tracing: OpenTelemetry (벤더 무관)

spring-cloud-kubernetes로 K8s API 통합.