Trace context is not propagated to Netty access logs

Describe the bug When Reactor Netty access log is enabled and reactor signals are published on different scheduler, then there is no trace info in access logs. If same scheduler is used, trace context is propagated and correctly printed in access log.

Trace context should also be propagated to access log so we can correlate application logs with access logs.

Spring Cloud version: 2020.0.2 Spring Sleuth version: 3.0.2

Sample Use Spring Initializer with Spring Reactive Web and Sleuth (in my case with Kotlin). Add controller:

@RestController
class Controller {
	private val logger = LoggerFactory.getLogger(javaClass)

	@GetMapping("test1")
	fun test1() = Mono.just("response")
		.doOnNext {
			logger.info("Test1")
		}

	@GetMapping("test2")
	fun test2() = Mono.just("response")
		.doOnNext {
			logger.info("Test2 - before publishOn")
		}
		.publishOn(Schedulers.boundedElastic())
		.doOnNext {
			logger.info("Test2 - after publishOn")
		}
}

Start application with -Dreactor.netty.http.server.accessLogEnabled=true GET http://localhost:8080/test1 correctly prints spanId & traceId

2021-05-25 09:45:53.357  INFO [,dc579da470f010ee,dc579da470f010ee] 31692 --- [ctor-http-nio-4] com.example.demo.Controller              : Test1
2021-05-25 09:45:53.357  INFO [,dc579da470f010ee,dc579da470f010ee] 31692 --- [ctor-http-nio-4] reactor.netty.http.server.AccessLog      : 127.0.0.1:52134 - - [25/May/2021:09:45:53 +0200] "GET /test1 HTTP/1.1" 200 8 0 ms

GET http://localhost:8080/test2 spanId & traceId is missing in access log

2021-05-25 09:45:55.990  INFO [,172cd6fa0e60cb81,172cd6fa0e60cb81] 31692 --- [ctor-http-nio-5] com.example.demo.Controller              : Test2 - before publishOn
2021-05-25 09:45:55.990  INFO [,172cd6fa0e60cb81,172cd6fa0e60cb81] 31692 --- [oundedElastic-2] com.example.demo.Controller              : Test2 - after publishOn
2021-05-25 09:45:55.990  INFO [,,] 31692 --- [ctor-http-nio-5] reactor.netty.http.server.AccessLog      : 127.0.0.1:52135 - - [25/May/2021:09:45:55 +0200] "GET /test2 HTTP/1.1" 200 8 0 ms

[qavid]

@violetagg many thanks. Trace context is now printed in access log with reactor-netty-http-brave 1.0.8-SNAPSHOT.

[qavid]

@marcingrzejszczak I have created PR to sleuth-issues repo: https://github.com/spring-cloud-samples/sleuth-issues/pull/67