Open Stack

On Wed, Aug 31, 2016 at 6:02 PM, Clint Byrum <clint at fewbar.com> wrote:
> 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.
>

+1 I'm certainly interested in helping out here.



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-- 
Ken Giusti  (kgiusti at gmail.com)