[openstack-dev] [nova] Boston Forum session recap - claims in the scheduler (or conductor)

Matt Riedemann mriedemos at gmail.com
Fri May 19 13:48:02 UTC 2017

On 5/19/2017 8:14 AM, Chris Dent wrote:
> On Thu, 18 May 2017, Matt Riedemann wrote:
>> We didn't really get into this during the forum session, but there are 
>> different opinions within the nova dev team on how to do claims in the 
>> controller services (conductor vs scheduler). Sylvain Bauza has a 
>> series which uses the conductor service, and Ed Leafe has a series 
>> using the scheduler. More on that in the mailing list [3].
> Since we've got multiple threads going on this topic, I put some
> of my concerns in a comment on one of Ed's reviews:
>      https://review.openstack.org/#/c/465171/3//COMMIT_MSG@30
> It's a bit left fieldy but tries to ask about some of the long term
> concerns we may need to be thinking about here, with regard to other
> services using placement and maybe them needing a
> scheduler-like-thing too (because placement cannot do everything).
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Thanks for pointing this out Chris. I still need to read Ed's blog post 
(separate thread), but we've said for a few releases now that the 
long-term goal is to split placement out of nova, and leave 
nova-scheduler within nova, since the scheduler code is very 
nova-specific (think of all the affinity sync stuff).

I appreciate thinking big and long-term, but I really don't want to 
spend a lot of time right now questioning every move we make and whether 
that might hurt the ability to split the scheduler code out in 5 years 
because some other project wants to use it - which is Gantt 2.0 and I 
haven't heard any other project express an interest in something like that.

I don't know how other projects do claims today, and how different they 
are from how nova does them. So there would seem to be a lot of 
discovery involved before we could even go down that path, not to 
mention all of the nova-specific code that would need to come out of the 
scheduler, or be made generic/pluggable.

Again, I think if we spend too much time thinking about that we're not 
going to get anything done in Pike.




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