Support "service" tag

[yurishkuro]

Rebooking from jaegertracing/jaeger-client-java#490.

Requirement - what kind of business use case are you trying to solve?

OpenTracing specification added service tags: opentracing/specification@f7ca62c

Problem - what in Jaeger blocks you from solving the requirement?

There's no special handing for the service tag in Jaeger right now.

Proposal - what do you suggest to solve the problem or improve the existing situation?

Add an adjuster (https://github.com/jaegertracing/jaeger/tree/master/model/adjuster) that will read the service tag from the span and update the span.process.serviceName field.

Any open questions to address

As I mentioned (opentracing/specification#77 (comment)) previously, Jaeger tracers use multiple attributes in the Process object to identify the service. The service tag only overrides the service name, but attributes like process.tags["ip"] will be set to the IP of the process creating the span (e.g. a service mesh). This might be confusing when looking at the traces in the UI, or worse it could affect some other logic like the clock skew adjustment.

[jpkrohling]

cc @mustafaakin it's yours, if you want to work on it :)

[mustafaakin]

I am working on it @jpkrohling thanks!

[quaff]

Any updates?

[objectiser]

I think we may want to hold off on this until we know the outcome of opentracing/specification#131

[pavolloffay]

The referenced PR mostly changes OT API. The processing on the server side would be probably similar/the same as what we have previously discussed here. The open question is what tag will we use as the proposed API allows to use basically an arbitrary tag.

[yurishkuro]

The service tag has been pulled out of OT Spec.