[Messaging RabbitMQ] What to use for `destination.name` when the default exchange is used (empty string)

[joaopgrassi]

Area(s)

area:messaging

Is your change request related to a problem? Please describe.

In the RabbitMQ conventions we say:

In RabbitMQ, the destination is defined by an exchange and a routing key. messaging.destination.name MUST be set to the name of the exchange. This will be an empty string if the default exchange is used.

In Java, the RabbitMQ instrumentation uses <default> in case the exchange name is empty (default one is used).

It is also "confusing" that we say a destination is composed of exchange and routing key, but we don't say how or if even the routing key is supposed to be part of the destination name attribute.

Describe the solution you'd like

Given there are clients for many languages, the conventions should specify what to use when the default exchange is used. Right now, each language can do their own thing, resulting in inconsistent behavior/value for the destination.name attribute.

Describe alternatives you've considered

No response

Additional context

Java example:
https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/main/instrumentation/rabbitmq-2.7/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/rabbitmq/RabbitDeliveryAttributesGetter.java#L41

[joaopgrassi]

In .NET it is using amq.default https://github.com/rabbitmq/rabbitmq-dotnet-client/blob/main/projects/RabbitMQ.Client/Impl/RabbitMQActivitySource.cs#L178

Python seems to use the routing queue if the exchange is the default: https://github.com/open-telemetry/opentelemetry-python-contrib/blob/main/instrumentation/opentelemetry-instrumentation-pika/src/opentelemetry/instrumentation/pika/utils.py#L69