When exporting metrics to Kafka, each resource type has an entity. For physical interfaces, it is defined like this:
Considering that interface resources are especial, and it is the ifIndex that identifies a resource (a.k.a., instance), that Protobuf field should be populated with:
Unfortunately, that is not the case:
I don't think there is any usefulness in using the interface label (which is what the "getInterfaceLabel" method provides) as the instance here.
The correct behavior is that the instance should point to the ifIndex (i.e., use the "getInstance" method), to be consistent with the other resources (if you scroll down, you'll see that for Generic Index Resources, that is what it is used).
If someone needs the interface name, assuming there is a need for that, it is better to add it as a new field in the Protobuf content.