Open Stack

Excerpts from Ian Wells's message of 2016-08-31 12:30:45 -0700:
> On 31 August 2016 at 10:12, Clint Byrum <clint at fewbar.com> wrote:
> 
> > Excerpts from Duncan Thomas's message of 2016-08-31 12:42:23 +0300:
> > > On 31 August 2016 at 11:57, Bogdan Dobrelya <bdobrelia at mirantis.com>
> > wrote:
> > >
> > > > I agree that RPC design pattern, as it is implemented now, is a major
> > > > blocker for OpenStack in general. It requires a major redesign,
> > > > including handling of corner cases, on both sides, *especially* RPC
> > call
> > > > clients. Or may be it just have to be abandoned to be replaced by a
> > more
> > > > cloud friendly pattern.
> > >
> > >
> > > Is there a writeup anywhere on what these issues are? I've heard this
> > > sentiment expressed multiple times now, but without a writeup of the
> > issues
> > > and the design goals of the replacement, we're unlikely to make progress
> > on
> > > a replacement - even if somebody takes the heroic approach and writes a
> > > full replacement themselves, the odds of getting community by-in are very
> > > low.
> >
> > Right, this is exactly the sort of thing I'd like to gather a group of
> > design-minded folks around in an Architecture WG. Oslo is busy with the
> > implementations we have now, but I'm sure many oslo contributors would
> > like to come up for air and talk about the design issues, and come up
> > with a current design, and some revisions to it, or a whole new one,
> > that can be used to put these summit hallway rumors to rest.
> >
> 
> I'd say the issue is comparatively easy to describe.  In a call sequence:
> 
> 1. A sends a message to B
> 2. B receives messages
> 3. B acts upon message
> 4. B responds to message
> 5. A receives response
> 6. A acts upon response
> 
> ... you can have a fault at any point in that message flow (consider
> crashes or program restarts).  If you ask for something to happen, you wait
> for a reply, and you don't get one, what does it mean?  The operation may
> have happened, with or without success, or it may not have gotten to the
> far end.  If you send the message, does that mean you'd like it to cause an
> action tomorrow?  A year from now?  Or perhaps you'd like it to just not
> happen?  Do you understand what Oslo promises you here, and do you think
> every person who ever wrote an RPC call in the whole OpenStack solution
> also understood it?
> 
> I have opinions about other patterns we could use, but I don't want to push
> my solutions here, I want to see if this is really as much of a problem as
> it looks and if people concur with my summary above.  However, the right
> approach is most definitely to create a new and more fitting set of oslo
> interfaces for communication patterns, and then to encourage people to move
> to the new ones from the old.  (Whether RabbitMQ is involved is neither
> here nor there, as this is really a question of Oslo APIs, not their
> implementation.)

I think it's about time we get some Architecture WG meetings started,
and put "Document RPC design" on the agenda.