shared subscription

[Jaimon Jose]

Hello,

I'm trying to switch one of our applications from another MQTT implementation to RabbitMQ with MQTT adapter.   One feature we use heavily is the shared subscriptions available in MQTTv5 where I can subscribe to topics from different nodes ($share/<group>/topic) and messages will be delivered to each node in the group in a roundrobin way.  I don't see any reference to shared subscription in RabbitMQ doc and the last reference in this group is from 2018.  Is there a way I can achieve same using RabbitMQ?  

Appreciate your help. 

[Wesley]

Hi

If I have understand you correctly, you can have multiple subscribers
consuming to the same queue, the messages will be delivered to all
subscribers by round robin.

Regards.

[Jaimon Jose]

Thank you.  I was expecting (like other implementations) the same messages to be delivered to all subscribers of a given topic.  If messages are delivered to multiple subscribers of a given topic by round robin, how do I implement a model where I expect all subscribers to receive same message?  

[Jaimon Jose]

I tested this scenario.  If two clients are subscribed to topic1/+/+, both are receiving all messages sent to topic1/*.  So, that's working as expected.  How do I subscribe if I want these two subscribers to receive messages in roundrobin? (we use this when subscribers are clustered as we expect only one of them to receive a given message. We use $share/<group>/ prefix for the topic to achieve this.)

[Warren Pang]

Hello

All consumers get the same messages, for this purpose you can declare the fanout exchange. All queues bonded to fanout exchange will get the same copy of a message.

Thanks 

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[Jaimon Jose]

I'm not clear about the suggestion of using fanout exchange. Could you elaborate on that? The context is shared subscription where the messages are delivered to subscribers in round robin.   in a shared subscription model, each message will be delivered to one of the subscribers if there are two subscribers for a topic. I'm trying to find out how to achieve this using rabbitmq+mqtt plugin.    

I do understand that all subscribers of a given topic will get all messages in normal case.  I verified that already.