[Tracing] Consistent span attribute key for CloudEvent id

[pierDipi]

MTBroker filter and ingress use messaging.message_id:

eventing/pkg/tracing/attributes.go

Lines 30 to 44 in 2e9f6a2

	MessagingMessageIDAttributeName = "messaging.message_id"
	)
	var (
	MessagingSystemAttribute trace.Attribute = trace.StringAttribute(MessagingSystemAttributeName, "knative")
	MessagingProtocolHTTP trace.Attribute = MessagingProtocolAttribute("HTTP")
	)
	func MessagingProtocolAttribute(protocol string) trace.Attribute {
	return trace.StringAttribute(MessagingProtocolAttributeName, protocol)
	}
	func MessagingMessageIDAttribute(ID string) trace.Attribute {
	return trace.StringAttribute(MessagingMessageIDAttributeName, ID)
	}

and the dispatcher uses cloudevents.id:

eventing/pkg/kncloudevents/populate_span_transformer.go

Lines 38 to 44 in 2e9f6a2

	if id != nil {
	idParsed, err := types.Format(id)
	if err != nil {
	return err
	}
	span.AddAttributes(trace.StringAttribute("cloudevents.id", idParsed))
	}

Expected Behavior

Consistently use one of them because using both is confusing.

Additional context

• The open telemetry spec defines messaging.message_id as follow:

  A value used by the messaging system as an identifier for the message represented as a string.
  

• cloudevents.id makes sense but it's not a well-known key for tracing.

---

Which one do we want to choose?

/area observability

[grantr]

Seems pretty obvious that we should use the standard messaging.message_id. This should be mentioned in the Knative eventing spec documents as as requirement for doing event tracing.

[xtreme-sameer-vohra]

Hey @pierDipi, @grantr,
I can take a look at this as a good first issue

I am going to make the assumption that since this is for tracing, we want to respect the Open Telemetry Spec (aka use messaging.* conventions)
and want the dispatcher

to be consistent with ingress and filtering

and hence we want to include the following attributes to the dispatcher trace

messaging.destination
messaging.message_id
messaging.protocol
messaging.system

[pierDipi]

Correct.