RabbitMq Mqtt : avoid redelivery or detect duplicate messages

[Kaveri P.H]

Hello All,

 

We are using RabbitMq Mqtt Broker with Paho Client for achieving an use case where sender and receiver interact.

 

We want to ensure that messages are NOT re-delivered to the receiver upon reconnection.

How do we ensure the same ? We are fine if we avoid redelivery of messages from Broker to Receiver or atleast detect duplicate arrivals at Receiver .

 

We are using configurations a) Clean Session as false b)  with QOS = 1 c) retain flag to true. We use the same client Id for reconnection.

Still , we receive the messages again ( without dup flag = true). Same behavior even if QOS = 0.

 

Please guide how to avoid redelivery or detection of duplicates mqtt messages.  Does QOS = 2 work with RabbitMq  Mqtt?

Kindly help.

Thanks & Regards,

Kaveri

[Arnaud Cogoluègnes]

RabbitMQ MQTT plugin doesn't support MQTT's QoS = 2.

With the configuration you're using (clean session = false and retain = true), the behavior is consistent with the specification. To avoid duplicates, you can set the retain flag to false (not ideal, disconnected consumers could miss messages). The best option is to make your consumers idempotent (duplicate-tolerant).

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[Michael Klishin]

QoS = 2 promises something that can only be delivered on when all cluster nodes and peers are coordinated.

This would introduce very substantial performance overhead and availability limitations.

Exactly once delivery is a myth: redeliveries are a fact of life in distributed systems. Exactly once *processing*

is certainly very much possible if you make your consumers idempotent.

Don't fall into the QoS 2 promise trap.

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MK

Staff Software Engineer, Pivotal/RabbitMQ