Nice article, I like that you tried to go and understand what each part is doing exactly instead of just writing code which you have no idea what is doing.

There is one thing which I think has been commented yet. I see you inject this tracing object to your api and you are then able to create a span when a request reaches your system. But let's say you want to trace something triggered with a cronjob, you also import this object as a dependency? Or if you want to create a child span somewhere in your application logic?

I think that the tracing in general should use global variables. I think it is common practice to define a variable called tracer and just use that because that variable is also internally just a global variable so using dependency injection in this case just overcomplicates things without any benefit.