Faas trace attributes: requirement levels need revision

[lmolkova]

faas trace semantic conventions define multiple attributes as required and some of these choices seem controversial:

• faas.document.time - it's required, but it's likely the same time as span start time. Is this attribute really needed? Should it be optional ?
• faas.time - same concern - it should match span start time, why another one is needed and can it be optional?
• faas.invoked_name span attribute that SHOULD match faas.name resource attribute, seems like duplication, why faas.invoked_name is needed and can it be optional?
• invoked_provider and invoked_region - should they be resource attributes (they are static)? should they be recommended instead?

[Oberon00]

faas.invoked_name span attribute that SHOULD match faas.name resource attribute, seems like duplication, why faas.invoked_name is needed and can it be optional?

It SHOULD match the remote side's faas.name, but that one might not be instrumented, or an error might occur with reaching it or transmission of the remote side's trace. Same with the other invoked_* attributes.
They cannot be resource attributes because you may call more than one different function (the same way an outgoing http.url cannot be a resource attribute).

For the first two (faas.time, faas.document.tme), I'd agree to make them "recommended".

[lmolkova]

Thanks for the clarification!
At least in Azure Functions world clients never know if they're calling an Azure Function or anything else. It sounds like the whole Outgoing Invocations is in manual instrumentation land or covers a few edge cases. Requiring anything, in this case, seems difficult.

[Oberon00]

It sounds like the whole Outgoing Invocations is in manual instrumentation land or covers a few edge cases.

No, this was introduced for AWS Lambda, where you have an API call to invoke a function (that can also be automatically instrumented with a hook mechanism). https://docs.aws.amazon.com/lambda/latest/dg/API_Invoke.html It seems that other cloud providers don't provide this mechanism though (except maybe Alibaba which seems to be, so it can't be sensibly set there (except manually indeed).

EDIT: Actually, Alibaba also seems to have that feature: https://www.alibabacloud.com/help/en/function-compute/latest/api-doc-fc-open-2021-04-06-api-doc-invokefunction

[jack-berg]

The language is also inconsistent in the faas trace semantic convention spec. Here it says that "it is recommended to set the following attributes", and proceeds to list a table of attributes which are all marked as "required".

[Oberon00]

Technically this would have the meaning that you SHOULD apply this semantic convention group. Which means you are allowed to leave it out completely, but if you choose to use the attributes, then you MUST fulfill the requirement levels of the table. Which allows having no special support for that trigger and still conforming to FaaS conventions, but if you do implement special support, some attributes are required.
(Not sure if the concrete required attributes make sense though)