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On 31 August 2016 at 22:30, Ian Wells <ijw.ubuntu at cack.org.uk> wrote:

> 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:
>> > 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?
>
>

Thank you for the explanation. Some times it is best to state the
apparently obvious just so that everybody is on the same page.

There are some pieces in cinder that attempt to work around some of these
limitations already, added with the recent H/A cinder-volume work.

-- 
Duncan Thomas
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