Ignoring client-proivded queue properties such as queue exclusivity when DQT is set

[Ayanda-D]

Community Support Policy

• I have read RabbitMQ's Community Support Policy

RabbitMQ version used

3.13.7 or older

How is RabbitMQ deployed?

Debian package

Steps to reproduce the behavior in question

Hi Team

We have the following scenario, which we'd like to bounce off for review:

• A new broker configured with rabbit.default_queue_type = quorum (cant be changed)
• Client applications that have been using exclusive classic queues (without specifying the explicit x-queue-type=classic) to be switched over to the new broker (and arent ready to migrate to quorum queues yet, since these dont support exclusive queues).
• Client code changes can take very long to x-queue-type=classic OR to set exclusive=false to work with the default_queue_type=quorum
• Eventually these code changes will be made, but as an immediate workaround, we want to have these users seamlessly use the new broker without any issues (protocol-errors).

This seems fit to be done via an interceptor plugin to manipulate queue.declare and implicitly switch/set the queue-type without clients having to make code changes, however, wanted to find out, is this something we can do at the broker level? e.g. via a config we can enable/disable that can allow/permit this behaviour.

[michaelklishin]

@Ayanda-D we have enough of one and off switches around quorum queues already.

Ignoring the exclusive property for quorum queues entirely is the only thing I'd agree to. I have asked the rest of the team.

[kjnilsson]

@Ayanda-D I dont understand why you want applications that currently use exclusive queues not to use exclusive queues in the new broker. Surely they chose to use exclusive queues cause they want the lifetime properties of an exclusive queue? Exclusive queues are always classic queues irrespective of default queue type settings.

[michaelklishin]

@Ayanda-D what you are asking for would turn the whole idea of default queue types upside down. default_queue_type is just that, a default, not an override. Client properties take precedence over defaults.

DQT and the code declaration path are already really complex, and that spills over to other features from native STOMP to definition export and import.

Furthermore, I fail to see why you'd want a queue that was previously exclusive queues would need to become quorum ones. Exclusive queues were never mirrored even in the CMQ era.

As for x-queue-type, there already is a feature that allows that particular property to be ignored during an equivalence check as of #8091:

quorum_queue.property_equivalence.relaxed_checks_on_redeclaration = true

Three people on our team out of three agreed that we should not change the current behavior, which is

1. If a client declares a queue as exclusive, it will be declared as an exclusive classic queue regardless of the DQT setting. Exclusive quorum queues or streams simply make no sense
2. That we do not need more features that modify RabbitMQ behavior to compensate for client libraries that explicitly tell it to do X but their (library) author now suddenly wants X to mean Y

[michaelklishin]

Client applications that have been using exclusive classic queues (without specifying the explicit
x-queue-type=classic) to be switched over to the new broker

Such declarations will continue declaring exclusive classic queues even if DQT is set to quorum or stream because only classic queues can be exclusive. Replicated exclusive queues or streams make no sense.

[michaelklishin]

quorum_queue.property_equivalence.relaxed_checks_on_redeclaration is now documented in rabbitmq.conf.example 9af2be3

[michaelklishin]

Plus rabbitmq/rabbitmq-website@92fb0a2

[Ayanda-D]

Thanks for explaining, confirming and clarifying the relaxed-checks config in the docs. We'll make use of this. & apologies, the issue was noticed and flagged from an existing long running 3.12.14 broker and indeed the behaviour we want was fixed and addressed in 9ba4d43 in the is_queue_args_combination_permitted(Q) check in newer versions, where exclusive=true on a quorum DQT will still default/fallback to a classic queue. We'll make it a point to test/check on latest/later versions next time to confirm issue still exists (still shaking off holiday vibes, sorry 😂 🙏 ).

Thanks! 👍