trace id is not propagated to access logs properly using reactor

[PH1P5]

Describe the bug
Creating a Spring WebFlux app with project reactor we recognized, that using Flux publisher the trace id is not logged in the access logs (via mdc).

Sample

https://github.com/PH1P5/reactor-sleuth-sample

We provided this sample repository to reproduce the issue. Please see all the necessary information in the README and also, logback-spring.xml and SampleController for further details.

@marcingrzejszczak investigating this bug we saw that you often were involved in similar discussions like:
#1748

We would really appreciate your help, thanks in advance

[PH1P5]

Could anyone please respond, we are currently working with a workaround which not fits our needs.

[marcingrzejszczak]

Let's start with the workaround. Please add the io.projectreactor.netty:reactor-netty-http-brave dependency and then set up the following configuration

@Configuration(proxyBeanMethods = false)
class Config {

	@Bean
	NettyServerCustomizer traceNettyServerCustomizer(ObjectProvider<HttpTracing> tracing) {
		return server -> ReactorNettyHttpTracing.create(tracing.getObject()).decorateHttpServer(server);
	}
}

that should work. Since this is actually a new feature and we're not planning to add any new features to Sleuth most likely we'll just document this.