RabbitMQ consumer on demand?

Question

I want a consumer to perform some actions every time that a message is received. Must the consumer be running 24/7 "listening" to the queue or it can be run only when an appropiate message is received?

Answer 1

I am not sure your question makes sense. The message can only be received from a queue by the consumer of a queue. To know if a message is in the queue one must look at the queue. The only way to do that is to be a consumer.

If you really want you could have a script that ran the commandline interface for the management plugin. That could poll the queue and when it had a size of more than one could start a program that would run a consumer to consume from the queue.

None of this makes any sense. If it is just sitting waiting for the queue and doing nothing else it is hardly consuming any resources so I do not see what the problem would be running a consumer 24/7.

Of course the consumer doesn't have to run 24/7, thats part of the point of MQ. It is asynchronous. The consumer does not have to be running when the producer writes to the queue. You could therefore have a scheduled task that runs your consumer periodically to check and process messages from the queue. But I do not think that is what you want.

The whole point of listening is: do nothing until a message comes, process the message, do nothing until the next message. This is what you want the first sentence of your question. Why the problem with listening?