Spring Microservices Skill

Master building cloud-native microservices with Spring Cloud including service discovery, centralized configuration, API gateway, and resilience patterns.

Overview

This skill covers the complete Spring Cloud ecosystem for production-grade microservices architecture.

Parameters

Name	Type	Required	Default	Validation
discovery	enum	✗	eureka	eureka | consul | kubernetes
gateway	enum	✗	spring-cloud-gateway	spring-cloud-gateway | zuul
resilience	enum	✗	resilience4j	resilience4j | hystrix

Topics Covered

Core (Must Know)

• Service Discovery: Eureka Server/Client, service registration
• API Gateway: Spring Cloud Gateway, routing, filters
• Configuration: Spring Cloud Config Server/Client
• Load Balancing: Spring Cloud LoadBalancer

Intermediate

• Resilience: Circuit breaker, retry, timeout, bulkhead
• Distributed Tracing: Micrometer Tracing, Zipkin
• Inter-Service Communication: RestClient, Feign

Advanced

• Event-Driven: Spring Cloud Stream, Kafka, RabbitMQ
• Service Mesh: Kubernetes integration
• Multi-Region: Cross-region deployment patterns

Code Examples

Eureka Server

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

# application.yml
server:
  port: 8761
eureka:
  client:
    register-with-eureka: false
    fetch-registry: false

Spring Cloud Gateway

@Configuration
public class GatewayConfig {

    @Bean
    public RouteLocator routes(RouteLocatorBuilder builder) {
        return builder.routes()
            .route("user-service", r -> r
                .path("/api/users/**")
                .filters(f -> f
                    .stripPrefix(1)
                    .circuitBreaker(c -> c.setName("userCB").setFallbackUri("forward:/fallback"))
                    .retry(retryConfig -> retryConfig.setRetries(3)))
                .uri("lb://USER-SERVICE"))
            .build();
    }
}

Resilience4j Circuit Breaker

@Service
public class OrderClient {

    @CircuitBreaker(name = "orderService", fallbackMethod = "fallback")
    @Retry(name = "orderService")
    public List<Order> getOrders(Long userId) {
        return restClient.get()
            .uri("/orders?userId={userId}", userId)
            .retrieve()
            .body(new ParameterizedTypeReference<>() {});
    }

    public List<Order> fallback(Long userId, Throwable t) {
        log.warn("Fallback for userId: {}", userId);
        return Collections.emptyList();
    }
}

# resilience4j configuration
resilience4j:
  circuitbreaker:
    instances:
      orderService:
        failure-rate-threshold: 50
        wait-duration-in-open-state: 30s
        sliding-window-size: 10
  retry:
    instances:
      orderService:
        max-attempts: 3
        wait-duration: 1s

Distributed Tracing

management:
  tracing:
    sampling:
      probability: 1.0
  zipkin:
    tracing:
      endpoint: http://localhost:9411/api/v2/spans

logging:
  pattern:
    level: "%5p [${spring.application.name},%X{traceId:-},%X{spanId:-}]"

Troubleshooting

Failure Modes

Issue	Diagnosis	Fix
Service not registered	Wrong Eureka URL	Check eureka.client.serviceUrl
Gateway 503	No instances	Check service health
Circuit always open	Threshold too low	Adjust failure rate

Debug Checklist

□ Check Eureka dashboard: http://localhost:8761
□ Verify gateway routes: /actuator/gateway/routes
□ Check circuit breaker state: /actuator/circuitbreakers
□ Test config refresh: POST /actuator/refresh

Unit Test Template

@SpringBootTest
@WireMockTest(httpPort = 8089)
class OrderClientTest {

    @Autowired
    private OrderClient orderClient;

    @Test
    void shouldReturnOrdersWhenServiceAvailable() {
        stubFor(get(urlPathEqualTo("/orders"))
            .willReturn(aResponse()
                .withStatus(200)
                .withBody("[]")));

        List<Order> orders = orderClient.getOrders(1L);
        assertThat(orders).isEmpty();
    }

    @Test
    void shouldUseFallbackWhenServiceDown() {
        stubFor(get(urlPathEqualTo("/orders"))
            .willReturn(aResponse().withStatus(503)));

        List<Order> orders = orderClient.getOrders(1L);
        assertThat(orders).isEmpty(); // fallback
    }
}

Usage

Skill("spring-microservices")

Version History

Version	Date	Changes
2.0.0	2024-12-30	Resilience4j, Micrometer Tracing, gateway patterns
1.0.0	2024-01-01	Initial release