Custom Request-Id for client side requests

[emanuel-v-r]

On every new request, aspnetcore creates a new Activity and sets a RequestId, TraceId, and SpanId, and spans it through the logs.
Is it possible to somehow set the ParentId to a UUID coming from the client-side (javascript) via a custom HTTP header?
I understand that if this UUID comes in the Request-Id HTTP header it automatically uses it, but what if it comes in a different custom header?
Thank you.

[davidfowl]

Client as in JavaScript or .NET client?

[emanuel-v-r]

Client as in JavaScript or .NET client?

Javascript client, calling this service from the UI. This way we would be able to track down the whole path of a request coming from the browser.
As I understand Request-Id header is already automatically added to requests happening on the .NET side (at least when using HttpClientFactory).

[adityamandaleeka]

@Tratcher @noahfalk This should be possible now right?

[Tratcher]

It can be customized, I just need to find the example.

Here's the code in hosting, it uses a DistributedContextPropagator.

aspnetcore/src/Hosting/Hosting/src/Internal/HostingApplicationDiagnostics.cs

Lines 286 to 292 in 73db5e4

	_propagator.ExtractTraceIdAndState(headers,
	static (object? carrier, string fieldName, out string? fieldValue, out IEnumerable<string>? fieldValues) =>
	{
	fieldValues = default;
	var headers = (IHeaderDictionary)carrier!;
	fieldValue = headers[fieldName];
	},

The only reference I can find is https://devblogs.microsoft.com/dotnet/announcing-net-6-preview-7/#libraries-system-diagnostics-propagators, but @noahfalk would know better.

[cijothomas]

On every new request, aspnetcore creates a new Activity and sets a RequestId, TraceId, and SpanId, and spans it through the logs. Is it possible to somehow set the ParentId to a UUID coming from the client-side (javascript) via a custom HTTP header? I understand that if this UUID comes in the Request-Id HTTP header it automatically uses it, but what if it comes in a different custom header? Thank you.

This should be possible custom "propagators" (dotnet/runtime#50658). The default propagator respects the W3CTraceContext spec, i.e it looks for "traceparent" header (with a fallback to "request-id" to maintain back compact with legacy header).

[sebastienros]

This should be possible custom "propagators"

@cijothomas do you have any pointers to some documentation?

[sebastienros]

https://github.com/dotnet/runtime/blob/main/src/libraries/System.Diagnostics.DiagnosticSource/src/ActivityUserGuide.md

[cijothomas]

This should be possible custom "propagators"

@cijothomas do you have any pointers to some documentation?

Nothing other than the design proposal : dotnet/runtime#50658 (comment)

Thanks for contacting us.

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[emanuel-v-r]

Thank you all for the help here, I will analyze the source code in order to understand how to provide a custom propagator. Some documentation would be nice to have though.

[noahfalk]

@tarekgh @MihaZupan - did any documentation ever get created for the propagators feature? For example it would be ideal to have it documented together with our existing distributed tracing docs.

In the meantime if there are no docs I think the short story is roughly:

1. Implement a custom version of DistributedContextPropagator. You can use an existing implementation as a guide. If you want to change how new requests have their id populated then you want to change the implementation of ExtractTraceIdAndState. For example if you want the id to be read from a header called "MySpecialIdHeader" and there is no encoding for tracestate you could write:

public override void ExtractTraceIdAndState(object? carrier, PropagatorGetterCallback? getter, out string? traceId, out string? traceState)
        {
            if (getter is null)
            {
                traceId = null;
                traceState = null;
                return;
            }
            getter(carrier, "MySpecialIdHeader", out traceId, out _);
            traceState = null;
        }

If you need to handle the new header in addition to messages that use other more typical headers you can also consider falling back to check other headers when this one isn't present.

Also update the Fields property to enumerate any header names you might want to look up per-request.

2. Assign a new instance of your propagator to the static property DistributedContextPropagator.Current when your app starts up. This needs to happen before it is captured by the WebHostBuilder here.