[openstack-dev] [OSLO][RPC] AMQP / ZeroMQ control_exchange vs port numbers

Eric Windisch eric at cloudscaling.com
Wed Apr 24 14:10:34 UTC 2013

Sending aside sending, Ceilometer is already doing consumption
cross-project, receiving notifications from multiple control_exchanges (at
least where amqp is concerned).
On Apr 24, 2013 9:58 AM, "Russell Bryant" <rbryant at redhat.com> wrote:

> On 04/24/2013 09:47 AM, Eric Windisch wrote:
> > Discussing in regard to changing the ZeroMQ ipc directory,
> > and "allow to cast to other any control exchange"
> > https://review.openstack.org/27351
> > https://review.openstack.org/27346
> >
> > Basically, the fact that one can deploy each project on a different port
> > number with ZeroMQ is as close an equivalent (and best practice) as one
> > may get to AMQP's control_exchange.
> >
> > Even if we add artificial support for control_exchange to the ZeroMQ
> > driver (which is possible), this won't do Ceilometer any good if people
> > deploy ZeroMQ on different ports for different projects. Then, you'll
> > need to add a port= kwarg to cast/call/notify, in addition to the
> > control_exchange.  In fact, it seems likely that people will want to
> > deploy ZeroMQ on different ports for different projects, and we might
> > want to do this by default, so it *will* be a problem.
> >
> > Perhaps the best solution here is to bake in a numeric representation
> > for each control_exchange? We'd need to manage these for each
> > core/incubated project to prevent overlap. We already do this for the
> > control_exchange, although as a string there is little cost to doing so.
> > A bit more effort would be needed for tracking port assignments.
> Implementation details aside ... I'm actually curious why this is needed
> in the first place.  What's the use case driving the need for
> cross-project rpc calls?  This has been something we've avoided thus
> far.  rpc has been private to a given project.
> --
> Russell Bryant
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