Spring Boot3中WebClient用Brave时生成新TraceId的问题排查

我正在创建一个Spring Boot 3服务，需要与Spring Boot 2 Sleuth服务交互。已配置该Spring Boot 3应用通过WebClient传播B3 TraceId，但WebClient生成了另一个TraceId，未传播原有TraceId。

执行流程：访问http://localhost:8080端点，该端点会调用http://localhost:9090。

核心业务代码 #

@RestController
@SpringBootApplication
public class MyApplication {

  private static final Log logger = LogFactory.getLog(MyApplication.class);
  @Autowired WebClient.Builder builder;

  @RequestMapping("/")
  String home() {
    logger.info("Testing sending request to client");
    String data = builder
        .baseUrl("http://localhost:9090")
        .exchangeStrategies(ExchangeStrategies.builder().codecs(c ->
            c.defaultCodecs().enableLoggingRequestDetails(true)).build()
        )
        .build()
        .get()
        .exchangeToMono(res -> res.bodyToMono(String.class))
        .block();
    return data;
  }
}

B3追踪配置类 #

@Configuration
public class Config {
  @Bean
  public Tracing braveTracing() {
    return Tracing.newBuilder()
        .propagationFactory(
            B3Propagation.newFactoryBuilder()
                .injectFormat(B3Propagation.Format.MULTI)
                .build())
        .build();
  }
}

配置文件（application.properties） #

spring.application.name=demo
logging.level.org.springframework.web=TRACE
#spring.mvc.log-request-details=true
#spring.http.log-request-details=true

spring.codec.log-request-details=true
management.tracing.propagation.type=B3

logging.level.org.springframework.web.reactive.function.client.ExchangeFunctions=TRACE

management.tracing.enabled = true
management.tracing.sampling.probability = 1.0

Build.gradle依赖 #

implementation 'org.springframework.boot:spring-boot-starter-actuator'
implementation 'org.springframework.boot:spring-boot-starter-web'
implementation 'io.micrometer:micrometer-tracing-bridge-brave'
implementation 'org.springframework.boot:spring-boot-starter-webflux'
testImplementation 'org.springframework.boot:spring-boot-starter-test'

日志输出 #

2024-04-16T15:10:27.010-04:00 TRACE 34890 --- [demo] [nio-8080-exec-1] [121d49ff22764a67                -121d49ff22764a67] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped to com.example.demo.MyApplication#home()
2024-04-16T15:10:27.027-04:00 TRACE 34890 --- [demo] [nio-8080-exec-1] [121d49ff22764a67                -121d49ff22764a67] o.s.web.method.HandlerMethod             : Arguments: []
2024-04-16T15:10:27.028-04:00  INFO 34890 --- [demo] [nio-8080-exec-1] [121d49ff22764a67                -121d49ff22764a67] com.example.demo.MyApplication           : Testing sending request to client
2024-04-16T15:10:27.138-04:00 TRACE 34890 --- [demo] [nio-8080-exec-1] [121d49ff22764a67                -121d49ff22764a67] o.s.w.r.f.client.ExchangeFunctions       : [2f40d44] HTTP GET http://localhost:9090, headers=[X-B3-TraceId:"8089985fbcccddfa", X-B3-SpanId:"8089985fbcccddfa", X-B3-Sampled:"1"]

从日志可见，Spring Boot 3应用自身的TraceId为121d49ff22764a67，但WebClient发起请求时传播的却是8089985fbcccddfa，需解决WebClient传播原有TraceId的问题。

问题根源在于自定义的Tracing Bean，手动创建的Tracing实例未与Spring Boot的Micrometer Tracing上下文集成，导致WebClient无法获取当前线程的TraceId，进而生成新的TraceId。

修改步骤：

1. 移除自定义的Config类：Spring Boot会根据配置自动生成符合B3规范的Tracing实例，无需手动创建。
2. 保留自动配置的WebClient.Builder：当前代码已正确注入WebClient.Builder，无需修改，避免手动覆盖追踪相关配置。
3. 验证配置项：确保management.tracing.propagation.type=B3配置正确，该配置会自动启用B3格式的追踪传播。

修改完成后，WebClient会自动从当前请求上下文获取TraceId并传播，不再生成新的TraceId。

额外优化建议 #

避免在Spring MVC控制器中使用.block()阻塞调用WebClient，违背WebFlux非阻塞设计。建议将控制器方法改为返回Mono<String>：

@RequestMapping("/")
Mono<String> home() {
  logger.info("Testing sending request to client");
  return builder
      .baseUrl("http://localhost:9090")
      .exchangeStrategies(ExchangeStrategies.builder().codecs(c ->
          c.defaultCodecs().enableLoggingRequestDetails(true)).build()
      )
      .build()
      .get()
      .exchangeToMono(res -> res.bodyToMono(String.class));
}

既保持非阻塞特性，也能确保追踪上下文正确传递。

内容的提问来源于stack exchange，提问作者david