Improper child relationships with WebClient

[MarkRobbo]

Describe the bug
When WebClient requests are made and blocked to retrieve a result, subsequent calls are each parents of the previous request.

Now RestTemplate is being deprecated (https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/web/client/RestTemplate.html) it is becoming very common to include both web and webflux dependencies in the classpath and use WebClient as suggested by Spring to make blocking calls like this instead. Web takes priority for Servlet based applications.

In this case it becomes impossible to follow traces as every one is nested, especially between services.

Sample
Demo at https://github.com/MarkRobbo/cloud-schema-bug

I would expect to see these spans created by hitting /call happen one after another (each being s child of the first), but they are nested inside each other:

[marcingrzejszczak]

Can you show an example where you don't shoot a request to the same application? This types of tests do not work fine with Brave. Can you create 2 applications and show that the problem is still there?

[MarkRobbo]

Here is the same application as above but ran twice: one on 8080 (service1) and the other on 8081 (service2) by changing server.port and spring.application.name, then pointing one to the other for the calls to /1, /2 and /3 by changing the port on the WebClient

The same behaviour can be observed as when the app is hitting itself

(We also have this live in an environment with a large number of microservices and this obviously takes this problem to the extreme with everything being nested)

[marcingrzejszczak]

Ok, thanks, I'll check it out

[MarkRobbo]

Fixing this issue may also resolve #1423 which I believe is a symptom of this