[openstack-dev] [oslo][mistral] Saga of process than ack and where can we go from here...

Doug Hellmann doug at doughellmann.com
Tue May 3 21:45:47 UTC 2016

Excerpts from Joshua Harlow's message of 2016-05-03 14:24:13 -0700:
> Howdy folks,
> So I meet up with *some* of the mistral folks during friday last week at 
> the summit and I was wondering if we as a group can find a path to help 
> that project move forward in their desire to have some kind of process 
> than ack (vs the existing ack then process) in there usage of the 
> messaging layer.
> I got to learn that the following exists in mistral (sad-face):
> https://github.com/openstack/mistral/blob/master/mistral/engine/rpc.py#L38
> And it got me thinking about how/if we can as a group possibly allow a 
> variant of https://review.openstack.org/#/c/229186/ to get worked on and 
> merged in and release so that the above 'hack' can be removed.

Based on the comments on that patch, it looks like the consensus was to
add a new method (to the client & dispatcher & whatever else needs it)
to implement the new semantics. That way it's clear from the caller
side what is expected, and it even makes it possible to adopt the new
capability in other projects without having to go all-or-nothing.

That said, I agree with Mehdi that *most* RPC calls throughout OpenStack,
not being idempotent, should not use process-then-ack.


> I also would like to come to some kind of understanding that we also 
> (mistral folks would hopefully help here) would remove this kind of 
> change in the future as the longer term goal (of something like 
> https://review.openstack.org/#/c/260246/) would progress.
> Thoughts from folks (mistral and oslo)?
> Anyway we can create a solution that works in the short term (allowing 
> for that hack to be removed) and working toward the longer term goal?
> -Josh

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