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rabbitmqamqp

RabbitMQ: dropping messages when no consumers are connected

I'm trying to setup RabbitMQ in a model where there is only one producer and one consumer, and where messages sent by the producer are delivered to the consumer only if the consumer is connected, but dropped if the consumer is not present.

Basically I want the queue to drop all the messages it receives when no consumer is connected to it.

An additional constraint is that the queue must be declared on the RabbitMQ server side, and must not be explicitly created by the consumer or the producer.

Is that possible?

I've looked at a few things, but I can't seem to make it work:

  1. durable vs non-durable does not work, because it is only useful when the broker restarts. I need the same effect but on a connection.
  2. setting auto_delete to true on the queue means that my client can never connect to this queue again.
  3. x-message-ttl and max-length make it possible to lose message even when there is a consumer connected.
  4. I've looked at topic exchanges, but as far as I can tell, these only affect the routing of messages between the exchange and the queue based on the message content, and can't take into account whether or not a queue has connected consumers.

The effect that I'm looking for would be something like auto_delete on disconnect, and auto_create on connect. Is there a mechanism in rabbitmq that lets me do that?

Solution

  • After a bit more research, I discovered that one of the assumptions in my question regarding x-message-ttl was wrong. I overlooked a single sentence from the RabbitMQ documentation:

    Setting the TTL to 0 causes messages to be expired upon reaching a queue unless they can be delivered to a consumer immediately

    https://www.rabbitmq.com/ttl.html

    It turns out that the simplest solution is to set x-message-ttl to 0 on my queue.