Clarify if HTTP metrics semantic conventions require ALL the metrics to be implemented

[reyang]

What did you expect to see?

The HTTP metrics semantic convention spec should provide clarity "what is considered a compliant implementation", e.g. "an implementation is considered compliant if it has implemented all of the metrics described by this spec" or "an implementation is considered compliant if it has implemented at least one of the metrics described by this spec" or mark some metrics as REQUIRED and say "an implementation is considered compliant if and only if it has implemented ALL the REQUIRED metrics described by this spec".

Additional context.

The current spec has vague wording "The following metric instruments MUST be used to describe HTTP operations. They MUST be of the specified type and units."

[carlosalberto]

I don't think we have a definition for this anywhere, not even for tracing, right?

[reyang]

I don't think we have a definition for this anywhere, not even for tracing, right?

That's exactly why I opened this issue - in order for us to move semantic convention to Stable, we need to have clarity.

[nerdondon]

I'm pretty in the camp of having a certain set of metrics marked as required since that means there is a dependable interface. This does mean that the bar for marking more metrics as required would be a breaking change though.

[jsuereth]

So thinking about this a good bit. We want a "T-shaped" API. The idea being you have a set of known consistent http metrics that must be included for baseline observability. Instrumentation can go deeper (and we can do this with optional/allowed metrics), but we should have a baseline that is consistent for tooling & expectation purposes.

[jamesmoessis]

Would this be a simple boolean?

required ::= true | false 

Or would this follow a similar structure to attributes requirement level? i.e.

requirement_level ::= "required"
         |   "conditionally_required" <condition>
         |   "recommended" [condition] # Default if not specified
         |   "optional"

[arminru]

@jamesmoessis I created #3176 to discuss the desired levels and their definition (also beyond just HTTP).