openstack team mailing list archive

[Russell Bryant <rbryant@xxxxxxxxxx>]

On 04/25/2012 03:22 PM, Eric Windisch wrote:
> I've heard a few people mention pulling messages off the queue, or
> communicating via RPC outside of the project, or outside of Python. In
> theory, this sounds nice, but the RPC implementations are strictly
> making sure that A can execute calls on target B and that responses get
> back to A.
> 
> This has little to do with message queues, other than that message
> queues are optionally supported. You shouldn't be peeking behind that
> curtain. This is specific to each RPC mechanism and enforcing something
> this early might be more problematic than you expect.

I agree with you that any discussion of other things poking at the rpc
communications is broken and wrong.

The only case where it does make sense is notifications.  In that case,
the fact that it's using rpc is just an implementation detail.  If you
enable the rabbit notifier (should probably be renamed at some point),
there is a specific AMQP message exchange where external applications
are to receive notifications from nova.

This implementation detail means that this can also be used with zeromq
... though I'm not sure that makes sense.  There would probably be a
notifier implementation specific to zeromq that could make better use of
that messaging model.

-- 
Russell Bryant