Review and update OTel semantic conventions

[lmolkova]

I see a few minor discrepancies:

1. faas.trigger is set to some Azure Function constant like eventHubTrigger

Based on semantic conventions, I believe it should be pubsub - https://github.com/open-telemetry/semantic-conventions/blob/main/docs/faas/faas-spans.md and the fact that it's an Event Hub is captured in the corresponding messaging.system.

faas.trigger has the following list of well-known values. If one of them applies, then the respective value MUST be used; otherwise, a custom value MAY be used.

Value	Description	Stability
datasource	A response to some data source operation such as a database or filesystem read/write
http	To provide an answer to an inbound HTTP request
other	If none of the others apply
pubsub	A function is set to be executed when messages are sent to a messaging system
timer	A function is scheduled to be executed regularly

2. Very minor: ai.sdk.prefix = azurefunctions:4.1036.0.0 or dotnetiso:1.1.0.0 is populated on resources even when I don't use Application Insights SDK and use pure OTel like here https://github.com/lmolkova/testfuncotel. We probably should not set it if AppInsights is not enabled.

3. faas.version = 4.1036.0.0 is set on host resources, but it should not be set for Azure functions according to semconv

   Azure Functions: Not applicable. Do not set this attribute.

   Let's fix one side or the other.

4. faas.execution is used instead of faas.invocation_id. It was right according to OTel schema 1.17 which Functions support, but it was renamed later. Can we update the schema version for OTel case while it's all still experimental?

5. service.version on the host is reported as 4.1036.0.0 which does not seem right - it seems to be internal Function host version, but I assume users would expect it to be something about their code (if we can infer it).
   It maybe just something to document - the 4.1036.0.0 is probably automatically picked up by otel-dotnet from the assembly version and is probably easily overridden with OTEL env var.

Happy to discuss further and help if you'd like to change anything in the otel semantic conventions.

[stebet]

@RohitRanjanMS It would be awesome if the function host set the root span name to the faas.name or the HTTP method + http.route values for incoming HTTP requests. Currently the root spans are just named after the request method (GET, POST, etc.).

Example:

Would that make sense @lmolkova?

[lmolkova]

yep, I think it's not the case because http.route is not available for some reason. I wonder if we can force-update this activity name to {verb} {function name}.

Tried to check what FaaS semconv recommend and I think they are not clear enough - open-telemetry/semantic-conventions#1858

[stebet]

The trigger route is available from the Raw property on the context.FunctionMetadata here:

azure-functions-host/src/WebJobs.Script.Grpc/Channel/GrpcWorkerChannel.cs

Line 1724 in cfa63f6

Activity.Current?.AddTag(ResourceSemanticConventions.FaaSName, context.FunctionMetadata.Name);

Here's an example where the route property is fetched:

azure-functions-host/src/WebJobs.Script.WebHost/Extensions/FunctionMetadataExtensions.cs

Line 227 in cfa63f6

if (httpBinding.Raw != null && httpBinding.Raw.TryGetValue("route", StringComparison.OrdinalIgnoreCase, out JToken value))

I can try making a PR, I have no idea how easy or hard it is to run the host locally but let's see :)

[RohitRanjanMS]

This is done. Will be available in host 1039 release.