[rabbitmq-discuss] synchronized messages: through the queue and multiple consumers

[Martin Sustrik]

Hi,

We have a detailed article about implementing this kind of stuff over 
AMQP here:

http://wiki.openamq.org/tutorial:soa

It's not RabbitMQ, but as both products use AMQP, the solution should be 
almost identical.

Martin

Tony Garnock-Jones wrote:
> Hi Joe,
>
> joe lee wrote:
>   
>> I have two producers that need to send synchronized message to a queue,
>> where 1 of 3 consumers will consume the message.  In this scenario,
>> would the producer who sent the message, waits for the status back from
>> the consumer, that consumed the message?
>>     
>
> There's no provision for this kind of synchronisation embedded in AMQP,
> but it's the kind of thing that's easy to construct on top of AMQP.
>
>   
>> In synchronized messaging,
>> would producer and consumer talk directly to each other or the message
>> put in queue and consumer consume and reply back to the waiting producer?
>>     
>
> The latter - every communication is mediated by a queue.
>
> One way you could get what I think you're after would be to have a setup
> like the following diagram, where consumers get handed work items
> round-robin from the queue, and each item has a queue name in the
> "reply-to" field of the Basic Properties content header. When the
> consumer finishes the job, it replies to the producer by inserting a
> message in the reply queue found in the request, with the reply's
> "correlation-id" field set equal to the "correlation-id" field of the
> request. See, for example, classes RpcClient and RpcServer in the main
> RabbitMQ java client library.
>
>
> 	Producer   -----------------------\
> 	    ^				   \
> 	    |	  		      	    \
> 	       	  			     |
>        	Producer's			     |
>        	reply				     |
>        	queue				     v
>
> 	    ^				Service exchange
> 	    |
> 	    |
> 	    |				     |
> 	    |				     |
> 	    |				     v
> 	    |
> 	    | 			      Service queue
> 	    |
> 	    | 				     |
> 	    | 				     |
> 	    | 				     v
> 	    | 				     |
> 	    | 		              /------+------\
> 	    | 		             /       |	     \
> 	    | 		            |        |	      |
> 	    | 		            |        |	      |
> 	    |		            |        |	      |
> 	    |		            v  	     v 	      v
> 	    |
>  	    |		 Consumers: 1        2        3
> 	    |
> 	     \ 					      |
> 	      \					      /
> 	       \--------------------------------------
>
>
> Regards,
>   Tony
>