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

Russell Bryant rbryant at redhat.com
Wed Apr 24 13:56:26 UTC 2013

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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