281 basic distributed tracing

[Knappek]

Description

Added

• respect tracing headers for incoming HTTP requests
• add tracing info to SSE welcome_event

Closes #281

follow-up: #309

What to look out for

Dear reviewer, I want you to

• gain knowledge - I think it's important for you to know about the change.
• check that the code works on your machine.
• suggest implementation-code design/structure/readability improvements.
• suggest test-code design/structure/readability improvements.
• suggest documentation improvements.
• suggest language/writing improvements.
• help to find bugs (described below!).

Process

The goal is to improve not only the code in this PR but also our skills! The "rules":

• The review is considered "done" as soon as all reviewers have added their review, and all their comments have been addressed.
• For knowledge-sharing reviews, each reviewer should "approve" the PR after studying its content.
• After the approval, the merge is concluded by the developer.

ToDo

• Create child span and forward it
  • On API Gateway: take tracing and forward with new spanID to backend
    • Http: example
    • Kafka (fire and forget): example
    • Kinesis (fire and forget): example - this is not yet working with Jaeger/OpenZipkin; fails in opencensus plug
  • other direction: from backend to Frontend (here we only want to send traceparent to the frontend and not tracestate)
    • Kafka -> RIG -> Frontend: example
    • Kinesis -> RIG -> Frontend
    • Kafka -> RIG -> HTTP: ensure trace context is in http header
• Display at Jaeger

Have fun!

[Azer0s]

Just saw that you just added tracing for SSE. With the VConnection (which is hopefully being merged sometime soon), you can add tracing for all connection types (except for longpolling...but I'll try to get that working with the VConnection soon) in one fell swoop.

Just wanted to clarify so we don't end up with pesky merge conflicts 😄

[kevinbader]

changelog is missing