Add Distributed Tracing to the ASP.NET Core Documentation

[jamescrosswell]

The Laravel docs have a section on Distributed Tracing that explains what people need to do in the front end of their app to pass a propagation id through to the back end and trace between processes.

We should add something similar explaining what to do in a Razor template or something to the ASP.NET Core docs.

Originally raised on Discord.

[bruno-garcia]

Added this one more generically on the docs repo (as it's not just about .NET): getsentry/sentry-docs#8715

[petefox]

I can't believe I just came across this after two days of trying to figure out why this isn't working in asp.net core.

[jamescrosswell]

@bruno-garcia just checking what we're supposed to be doing here:

• The Laravel docs appear to describe a PHP helper function that will insert a couple of meta tags. Those meta tags would get used if the front end was instrumented using one of Sentry's javascript integrations (e.g. Browser Tracing)

In ASP.NET, there are quite a few different options for how you build your UI. There are Razor Pages in ASP.NET MVC, there are all the different modes for Blazor (Server/Client/Hybrid) and then there are SPAs.

It looks like the technique described in the Laravel docs would mostly be relevant if you had a SPA hooked up to your ASP.NET application right? I think that's the only scenario in which people are likely to be instrumenting the front end using Sentry's javascript integration.

I don't think we have any helper functions (yet) in .NET to generate those meta tags. We could create some and then document how these could be used in conjunction with a SPA application that was instrumented using Sentry. Is that what we're talking about here?

[jamescrosswell]

A related question: what's the best way for users of the .NET SDK to include instrumentation for their front end when they're not using a SPA? Ideally a transaction would start when a request was made from the front end to the back end right? That might be done using AJAX, SignalR (or something else for WASM maybe)? Do we have a mechanism to automatically instrument those requests starting with the request from the front end? It looks like we only instrument the middleware at the moment.

[bruno-garcia]

cc @smeubank @mydea for guidance here. How do we document this?

[clarity99]

I've tried adding this to the layout page:

 <meta name="sentry-trace" content="@SentrySdk.GetTraceHeader()?.TraceId.ToString()"/>
  <meta name="baggage" content="@SentrySdk.GetBaggage()?.ToString()"/>

However, now I am getting This trace has broken subtraces. Transactions linked by a dashed line have been orphaned and cannot be directly linked to the root., so something doesn't seem to work well.
Also, when I click on many traces since I made this change I get this: "The trace you are looking for was not found."

I guess this is not the correct way to go :)