How to add members / followers to quorum queue?

[peacock-el-gap]

Context
RabbitMQ running on K8s, 3 nodes.
Our application after connecting to RabbitMQ cluster declares necessary quorum queues (no queue declaration using configuration file).
RabbitMQ version: 3.11.2

Problem
When RabbitMQ cluster starts, application connects to first node, not waiting for other nodes and declares quorum queue. As a result such queue is populated only on this first node. I'm looking for a way do add members / followers to such queue when they are ready and connected to cluser.
I know, that it is possible using rabbitmq-queues CLI.

Questions

1. Is it possible to add members / followers to quorum queue using API?
2. Is there a way to configure RabbitMQ cluster, that new cluster node will be automatically added to each auorum queue as a follower?
3. What is the best approach to ensure, that quorum queues are distributed on all nodes connected to cluster, even if such nodes are connected after queue declaration? Note, that I wan to avoid queue declaration by config file - I want my application to declare queue but I want to avoid situation, that my application impmenents functionality needed to observe cluster nodes readiness. I also want to avoid situation that tha application should wait till RabbitMQ cluster is ready and all nodes are ready.

[michaelklishin]

The default quorum queue target replica count is 3, which is perfectly sufficient for a lot of cases.
This replication factor can be configured per queue.

There are also rabbitmq-queues grow and rabbitmq-queues shrink. There is also rabbitmq-queues rebalance which is supposed to be run after all cluster membership changes are complete, or all nodes are restarted during a rolling upgrade. See Managing Replicas.

[peacock-el-gap]

@michaelklishin, thank you for your anwser 😃.

As I stated in my post I understand, that we can use rabbitmq-queues CLI.
It is also true, that even if the default quorum queue target replica count is 3, it is not applied if node count is less then 3 during queue declaration.

How about my questions?
Especially - can I use API to grow queue? Is it possible or not?
Unfortunatelly API specification is not clear at this point 😢.

In API specification we can find information, that we can use PUT method for /api/queues/vhost/name endpoint.

To PUT a queue, you will need a body looking something like this:
{"auto_delete":false,"durable":true,"arguments":{},"node":"rabbit@smacmullen"}

I've tried PUT with several options to add members / followers, but without success.

[mkuratczyk]

I don't think there is an API to achieve that.

There is a work-in-progress PR to periodically validate quorum queue membership:
#8218

The issue you are seeing is something we discussed in the past: #3850
I still believe we should not accept a declaration in the first place. The question remains what the behaviour should be (rejection, internal wait/retry that looks like a very slow declaration from the application's perspective or what)

[peacock-el-gap]

@mkuratczyk, thanx for your reply.
I agree that in such situation declaration should not be accepted. Rejection is my favourite behaviour, however I'm not sure, if I understand all consequences.

Topic closed.