Add schema URL support

[cijothomas]

Spec requires Meter, Tracer(ActivitySource) to have a 3rd parameter schemaUrl.
https://github.com/open-telemetry/opentelemetry-specification/pull/1666/files

As both these classes are part of .NET Runtime, we need to request this change in .NET Runtime repo. Opening an issue here first to see if there is any alternatives in the meantime, and to track this (for consideration in next .NET release)

[cijothomas]

related spec PR: open-telemetry/opentelemetry-specification#2180

[cijothomas]

Once the semantic conventions becomes stable, the instrumentation libraries can go stable. But they'll need schema_url support to point to the version of the semantic conventions its implementing.

[samsp-msft]

Seems like a potential dupe of #4316 - If we added a dictionary to Meter and ActivitySource you can use a well-known key name for the URL. There is an existing precedent in the Resource API which is a dictionary and semantic conventions for the key names.

[pellared]

How are you planning to stabilize any instrumentation library or resource detector without this feature?

If the telemetry producers do not set the schema URL then they fall into "Fixed Schema Telemetry Producers" and therefore:

Instrumentations that are labeled Stable and do not include the Schema URL in the produced telemetry are called Fixed Schema Telemetry Producers.

Such instrumentations are prohibited from changing any produced telemetry. If the specification changes over time and the semantic conventions are updated, the instrumentation is still prohibited from adopting the changes.

Source: https://opentelemetry.io/docs/specs/otel/telemetry-stability/

This feature is required by the specification for a very long time.
See:

• https://opentelemetry.io/docs/specs/otel/trace/api/
• https://github.com/open-telemetry/opentelemetry-specification/releases/tag/v1.4.0

@open-telemetry/dotnet-maintainers

Related comment: dotnet/runtime#63651 (comment)

[cijothomas]

Seems like a potential dupe of #4316 - If we added a dictionary to Meter and ActivitySource you can use a well-known key name for the URL. There is an existing precedent in the Resource API which is a dictionary and semantic conventions for the key names.

Not really a duplicate issue. This is still a separate issue, but it is possible to use a well known key in the Meter level tags and store schema_url there, and provide extension method (In OTel) like meter.GetSchemaUrl() which retrieves it from the well known key. I don't think such a thing was done in Resource, but we have done it for Activity.Status.

[github-actions]

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