[Openstack] [nova] why does notification use a "topic" exchange instead of "fanout"?

Doug Hellmann doug.hellmann at dreamhost.com
Tue May 8 23:52:22 UTC 2012


On Tue, May 8, 2012 at 7:42 PM, Monsyne Dragon <mdragon at rackspace.com>wrote:

> The reason nova uses a topic exchange and queues like it does is so the
> processing of notifications can be round-robined to multiple workers.  You
> should be able to open a new queue on the same exchange and receive copies
> of each message.
>

Yeah, this was a case of not reading enough (or the right) documentation.
The kombu docs didn't have an example of that, and I was having some
trouble mapping the Rabbit docs onto the kombu classes. I've got it working
the way I need now, though.

Thanks for your help,
Doug


>
> On May 8, 2012, at 3:19 PM, Doug Hellmann wrote:
>
> > I'm working on some code to monitor notification messages coming from
> nova by listening directly on the AMQP queue. Unfortunately, nova is using
> a topic exchange so it seems I can't safely consume the messages or they
> might not go to some other client that is expecting to see them (especially
> some other part of nova that is expecting to receive the notification). It
> seems like notifications should be available to more than one subscriber at
> a time, but I thought I would ask for background before I started working
> on a patch to change it.
> >
> > Is there a particular reason a topic exchange was used for notifications?
> >
> > Thanks,
> > Doug
> >
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> --
>        Monsyne M. Dragon
>        OpenStack/Nova
>        cell 210-441-0965
>        work x 5014190
>
>
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