MySQL spans do not link to the active parent span

[sstone1]

What version of OpenTelemetry are you using?

^0.21.0

What version of Node are you using?

v14.17.1

What did you do?

We are using OpenTelemetry in a LoopBack 4 application, which connects to a MySQL database and exposes a CRUD API over a database table. LoopBack 4 is built on top of the express, http and mysql libraries, so we are using the instrumentation for these.

What did you expect to see?

We expected to see a single trace for each HTTP request to the LoopBack 4 application, containing various spans - including a span for the request to the MySQL database.

What did you see instead?

We see two traces for each HTTP request to the LoopBack 4 application, one with all the HTTP spans, and another with just the MySQL span.

Additional context

I believe that this problem occurs as the context is getting lost when requesting a connection from the connection pool. I have a patch for the instrumentation code that fixes the problem by binding the callback for getConnection to the active context before passing it into the instrumented code.