[rabbitmq-discuss] STOMP Plugin: Alternative exchange other than amq.topic?

[Cliff Redmond]

Hi Steve,

thanks for your answer.

I was facing the exact same problem as Ken: I think your solution only
partially addresses the issue - requiring a subscription to a pre-
existing queue significantly reduces the flexibility of Stomp/
RabbitMQ.

One of the most useful features of the Stomp plugin is that when a
Stomp consumer subscribes to a topic, it automatically creates a new
queue (with a lifecycle dictated by the subscription) and binds it to
the default topic exchange on that broker.

e.g. invoking the following in a consumer:

$frame = Net::Stomp::Frame->new( {
      command => "SUBSCRIBE",
      headers => {
          destination => "/topic/durable-topic-prefetch",
          id => $subscriberId,
          persistent => "true",
          ack => "client",
          prefetch_count => 1,
      },
});

$stomp->send_frame($frame);

will create a queue on the relevant broker:

sh-3.2# rabbitmqctl list_queues
Listing queues ...
[...]
stomp.dsub.durable-topic-prefetch.?ܛ?R?M?\0006??1>?U	0
[...]
...done.

and bind it to the default topic exchange:

Listing bindings ...
[...]
amq.topic	exchange	stomp.dsub.durable-topic-prefetch.?ܛ?R?M?\0006??1>?
U	queue	durable-topic-prefetch	[]
[...]
...done.

Pre-configuring AMQ queues is considerably less flexible, and the
alternative, creating a queue (and binding it to an alternatively
named federated topic exchange) using AMQP before each Stomp
subscription, militates against using Stomp at all.

Would it be possible to make a change to either of the Stomp or
Federation plugins:

- be able to specify a topic exchange in the Stomp plugin config (i.e.
rather than have it always use amq.topic),
- be able to federate internal/predefined exchanges in the Federation
plugin.

(I used the Shovel plugin to workaround this issue).

Many thanks,

Cliff.

On Feb 21, 6:25 pm, Steve Powell <st... at rabbitmq.com> wrote:
> Hi Ken,
>
> It is possible for you to SEND to the exchange of your choice from aSTOMP
> application, using a destination of the form: /exchange/<name>/<pattern> (seehttp://www.rabbitmq.com/stomp.html#d.ed) and there is no reason why this
> shouldn't be a topic exchange of your own making.
>
> If you need to SUBSCRIBE to AMQP destinations you can use the destination
> /amq/queue/<name> (but the queue must exist).
>
> Between them, these should allow you to useSTOMPwith federated exchanges
> without plugin modifications.
>
> Let us know how you get on.
>
> Steve Powell  (a federated bunny)
> ----------some more definitions from the SPD----------
> vermin (v.) Treating the dachshund for roundworm.
> chinchilla (n.) Cooling device for the lower jaw.
> socialcast (n.) Someone to whom everyone is speaking but nobody likes.
>
> On 20 Feb 2012, at 16:19, Ken Simon wrote:
>
>
>
>
>
>
>
>
>
> > Greetings,
>
> > I'm trying to getfederationworking (via the rabbitmq_federation
> > plugin) in our environment ofSTOMPhosts, and to do so I have to
> > enablefederationin theSTOMPplugin's exchange: amq.topic.  This
> > unfortunately doesn't seem to work because amq.* exchanges are
> > reserved and cannot be re-declared.
>
> > My solution at this point has been to edit the source of theSTOMP
> > plugin and point it at an exchange called "stomp_topic" (which I made
> > up, but could be anything) instead of the default amq.topic.  Then I
> > just configure thefederationplugin to work with that exchange and it
> > works fine.
>
> > My question is, is there a better way of doing this?  I hate
> > maintaining my own downstream changes to plugins if I don't have to.
> > The docs say that theSTOMPplugin routes all messages through
> > amq.topic, so it appears that's not configurable.  But wouldn't it
> > make sense to allow use of an exchange that's not reserved?  Or am I
> > missing something, and this is actually way easier?  I'm having
> > trouble finding any documented cases of people using bothSTOMPand
> >federation.
>
> > Thanks,
>
> > --
> > Ken
> > _______________________________________________
> > rabbitmq-discuss mailing list
> > rabbitmq-disc... at lists.rabbitmq.com
> >https://lists.rabbitmq.com/cgi-bin/mailman/listinfo/rabbitmq-discuss
>
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