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On Wed, May 8, 2019 at 5:58 PM, Matt Riedemann <mriedemos at gmail.com> 
wrote:
> On 5/7/2019 2:19 AM, Balázs Gibizer wrote:
>> 3) The request pre-filters [7] run before the placement a_c query is
>> generated. But these today changes the fields of the RequestSpec 
>> (e.g.
>> requested_destination) that would mean the regeneration of
>> RequestSpec.requested_resources would be needed. This probably 
>> solvable
>> by changing the pre-filters to work directly on
>> RequestSpec.requested_resources after we solved all the other issues.
> 
> Yeah this is something I ran into while hacking on the routed 
> networks aggregate stuff [1]. I added information to the RequestSpec 
> so I could use it in a pre-filter (required aggregates) but I can't 
> add that to the requested_resources in the RequestSpec without 
> resources (and in the non-bw port case there is no 
> RequestSpec.requested_resources yet), so what I did was hack the 
> unnumbered RequestGroup after the pre-filters and after the 
> RequestSpec was processed by resources_from_request_spec, but before 
> the code that makes the GET /a_c call. It's definitely ugly and I'm 
> not even sure it works yet (would need functional testing).
> 
> What I've wondered is if there is a way we could merge request groups 
> in resources_from_request_spec so if a pre-filter added an unnumbered 
> RequestGroup to the RequestSpec (via the requestd_resources 
> attribute) that resources_from_request_spec would then merge in the 
> flavor information. That's what I initially tried with the 
> multiattach required traits patch [2] but the groups weren't merged 
> for whatever reason and GET /a_c failed because I had a group with a 
> required trait but no resources.
> 

If we only need to merge once then it feels doable. We just add new 
things to the pre-existing unnumbered group from the flavor and image. 
But if we ever need to update what we already merged into the 
unnumbered group then we would need access to the old flavor / image to 
first subtract them from the unnumbered group and then add the requests 
from the new flavor / image to the unnumbered group.

The other way would be to store the extra traits separately as well in 
the RequestSpec and only generate the unnumbered group from all the 
input when needed.

Cheers,
gibi

> [1] https://review.opendev.org/#/c/656885/3/nova/scheduler/manager.py
> [2] https://review.opendev.org/#/c/645316/
> 
> --
> 
> Thanks,
> 
> Matt
>