Spring Cloud进阶：熔断、限流与链路追踪

概述

微服务架构需要完善的治理机制。本教程介绍熔断、限流和链路追踪的实现。

1. 熔断器（Resilience4j）

import io.github.resilience4j.circuitbreaker.annotation.CircuitBreaker;
import io.github.resilience4j.retry.annotation.Retry;
import io.github.resilience4j.timelimiter.annotation.TimeLimiter;
import org.springframework.stereotype.Service;

@Service
public class ResilienceService {
    
    @CircuitBreaker(name = "userService", fallbackMethod = "fallback")
    public String callExternalService() {
        // 可能失败的外部调用
        return restTemplate.getForObject("http://external-service/api", String.class);
    }
    
    @Retry(name = "userService")
    public String retryableService() {
        // 可重试的操作
        return callExternalService();
    }
    
    public String fallback(Throwable t) {
        return "降级响应";
    }
}

# application.yml
resilience4j:
  circuitbreaker:
    instances:
      userService:
        slidingWindowSize: 10
        failureRateThreshold: 50
        waitDurationInOpenState: 10s
        permittedNumberOfCallsInHalfOpenState: 3
  retry:
    instances:
      userService:
        maxAttempts: 3
        waitDuration: 500

2. 限流（Sentinel）

import com.alibaba.csp.sentinel.annotation.SentinelResource;
import com.alibaba.csp.sentinel.slots.block.BlockException;
import org.springframework.stereotype.Service;

@Service
public class RateLimitingService {
    
    @SentinelResource(value = "limitedResource", blockHandler = "handleBlock")
    public String limitedResource() {
        return "正常响应";
    }
    
    public String handleBlock(BlockException ex) {
        return "限流响应";
    }
}

# application.yml
spring:
  cloud:
    sentinel:
      transport:
        dashboard: localhost:8080
      datasource:
        flow:
          nacos:
            server-addr: localhost:8848
            data-id: flow-rules
            group-id: SENTINEL_GROUP

3. 链路追踪（Sleuth + Zipkin）

import brave.sampler.Sampler;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class TracingConfig {
    @Bean
    public Sampler defaultSampler() {
        return Sampler.ALWAYS_SAMPLE;
    }
}

# application.yml
spring:
  sleuth:
    sampler:
      probability: 1.0
  zipkin:
    base-url: http://localhost:9411

4. 实际应用示例

熔断降级

@Service
public class OrderService {
    private final UserClient userClient;
    private final ProductClient productClient;
    
    @CircuitBreaker(name = "user-service", fallbackMethod = "getUserFallback")
    public User getUser(Long userId) {
        return userClient.getUser(userId);
    }
    
    @CircuitBreaker(name = "product-service", fallbackMethod = "getProductFallback")
    public Product getProduct(Long productId) {
        return productClient.getProduct(productId);
    }
    
    public User getUserFallback(Long userId, Throwable t) {
        return new User(userId, "未知用户", 0);
    }
    
    public Product getProductFallback(Long productId, Throwable t) {
        return new Product(productId, "未知商品", 0.0);
    }
}

分布式日志

import org.slf4j.MDC;
import org.springframework.web.filter.OncePerRequestFilter;

public class TracingFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, 
                                   HttpServletResponse response, 
                                   FilterChain filterChain) {
        String traceId = request.getHeader("X-Trace-Id");
        MDC.put("traceId", traceId);
        
        try {
            filterChain.doFilter(request, response);
        } finally {
            MDC.clear();
        }
    }
}

5. 最佳实践

1. 熔断降级：保护系统免受级联故障
2. 限流控制：防止系统过载
3. 链路追踪：快速定位问题
4. 监控告警：实时监控系统状态
5. 容错设计：设计高可用的微服务

总结

熔断、限流和链路追踪是微服务治理的重要组成部分。掌握这些技术，可以构建稳定、可靠的微服务系统。