OpenTelemetry tracing of Dbus calls

[Thomas Kluyver]

Hi Umut,

On Wed, 11 Jan 2023, at 10:09, Umut Tezduyar Lindskog wrote:
> We have around 40-50 dbus services which are the backends to http APIs. A backend might talk to other backends. We can easily trace the HTTP APIs but it would also be nice to add the dbus layer tracing to the overall picture. 

And are these services things that your organisation defines, or code written elsewhere? Or a mixture? How practical would it be to add tracing information to method call arguments, without any change to D-Bus itself? I'm not saying that's what you should do, just getting the shape of the problem.

> I think it is important to understand the dbus community's interest in OpenTelemetry. If the community is not interested then we can think about a downstream solution. But ideally we like to contribute. 

>From my perspective it's conceptually interesting, but I've never tried to use OpenTelemetry or anything similar to that; I only know the vague idea. I'm hoping other people will chime in, though.

I think you might be facing a kind of cultural barrier. The cloud/microservices world that I imagine you're coming from probably has far more sophisticated tracing and monitoring tools than the desktop Linux world that created D-Bus. Even with D-Bus, I don't think we have anything like as much need to follow things from one process to another.

> One other way that I can think of is a dedicated FD which carries the context data. This, of course, also needs changes in the client libraries. 

Is there a specific reason you suggest a file descriptor? It would need spec changes and client library changes either way, there's extra complexity involved in sending & receiving FDs, and it's not always possible - e.g. D-Bus can be used on Windows, even though its main use cases are on Linux. So I'd assume a solution that adds simple data in the messages would be preferred to one using an FD.

Best wishes,
Thomas
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