Comment 2 for bug 1905965

Thanks for the input John. You are correct - the current implementation of oslo.messaging does not use the special Direct Reply To feature provided by rabbitmq [0]. Whether or not it should is an entire discussion in itself :D

Currently oslo.messaging uses a "somewhat long lived" reply queue that is associated with the direct exchange. It is "somewhat long lived" in that its lifecycle is associated with the client's transport, and therefore will be used for all requests issued by the client (each individual request is identified by a correlation id - essentially multiplexing replies on the same queue).

Back the the issue at hand: if I understand you correctly oslo.messaging's current use of the mandatory flag - to force an error exception on the server when the reply cannot be delivered - is correct. Logically it seems correct to me as well.

However from the user's point of view (in the case nova) it's a breaking API change. Mea culpa - turning on the mandatory feature by default should not have been done without making a whole lot more public noise than I did.

Sounds like the best path forward would be to turn off the mandatory behavior by default (it's configurable) until folks have a chance to update their code to handle the new behavior.

[0] https://www.rabbitmq.com/direct-reply-to.html