pkg/receive: eliminate duplicate tracing

[squat]

The receive component currently has duplicate spans for requests handled
by its HTTP server. This is due to the fact that the server is
instrumented once using the global singleton tracer and then a second
time with the tracer configured via the CLI. This commit eliminates the
duplicate instrumentation via the global singleton in favor of the
explicit specified tracer, which is consistent with the practice of
other Thanos components.

Signed-off-by: Lucas Servén Marín [email protected]

Example of duplicate span:

Note that:

• both /receive HTTP[server] and POST /api/v1/receive represent the same operation; and that
• the span created by the global singleton, POST /api/v1/receive is erroneously setting the HTTP status code to 0.

[metalmatze]

Cool, this should declutter things, thanks!
Is Thanos using a global object that everything references? However, the Prometheus registry is passed by reference?

[bwplotka]

Nicely spotted, thanks!

[squat]

@metalmatze the tracing configuration is also typically passed explicitly, e.g. https://github.com/thanos-io/thanos/blob/master/cmd/thanos/query.go#L382,
https://github.com/thanos-io/thanos/blob/master/cmd/thanos/query.go#L400.

The receive component was the only component with a reference to the globaltracer, however this seems to have been left over from the initial implementation of the receiver.