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On Mon, Aug 29, 2016, at 08:20 AM, Jay Pipes wrote:
> On 08/29/2016 05:11 AM, Sylvain Bauza wrote:
> > Le 29/08/2016 13:25, Jay Pipes a écrit :
> >> On 08/26/2016 09:20 AM, Ed Leafe wrote:
> >>> On Aug 25, 2016, at 3:19 PM, Andrew Laski <andrew at lascii.com> wrote:
> >>>
> >>>> One other thing to note is that while a flavor constrains how much
> >>>> local
> >>>> disk is used it does not constrain volume size at all. So a user can
> >>>> specify an ephemeral/swap disk <= to what the flavor provides but can
> >>>> have an arbitrary sized root disk if it's a remote volume.
> >>>
> >>> This kind of goes to the heart of the argument against flavors being
> >>> the sole source of truth for a request. As cloud evolves, we keep
> >>> packing more and more stuff into a concept that was originally meant
> >>> to only divide up resources that came bundled together (CPU, RAM, and
> >>> local disk). This hasn’t been a good solution for years, and the
> >>> sooner we start accepting that a request can be much more complex
> >>> than a flavor can adequately express, the better.
> >>>
> >>> If we have decided that remote volumes are a good thing (I don’t
> >>> think there’s any argument there), then we should treat that part of
> >>> the request as being as fundamental as a flavor. We need to make the
> >>> scheduler smarter so that it doesn’t rely on flavor as being the only
> >>> source of truth.
> >>>
> >>> The first step to improving Nova is admitting we have a problem. :)
> >>
> >> FWIW, I agree with you on the above. The issue I had with the proposed
> >> patches was that they would essentially be a hack for a short period
> >> of time until the resource providers work standardized the way that
> >> DISK_GB resources were tracked -- including for providers of shared
> >> disk storage.
> >>
> >> I've long felt that flavors as a concept should be, as Chris so
> >> adeptly wrote, "UI furniture" and should be decomposed into their
> >> requisite lists of resource amounts, required traits and preferred
> >> traits and that those decomposed parts are what should be passed to
> >> the Compute API, not a flavor ID.
> >>
> >> But again, we're actively changing all this code in the resource
> >> providers and qualitative traits patches so I warned about adding more
> >> code that was essentially just a short-lived hack. I'd be OK adding
> >> the hack code if there were some big bright WARNINGs placed in there
> >> that likely the code would be removed in Ocata.
> >>
> >
> > While :
> > #1 the first change about setting root_gb equals 0 in RequestSpec for
> > making sure BFV instances are correctly using the DiskFilter is fine by
> > me having it merged with a TODO/FIXME saying that the code would be
> > expired once the scheduler uses the resource providers,
> > #2, then the second patch about trying to look at the BDMs for
> > DiskFilter is very wrong by me, because the Compute API shouldn't accept
> > IMHO to ask for a flavor *and* a BDM with a related disk size different
> > from the flavor. AFAIT, we should return a 40x (probably 409 or 400) for
> > that instead of accepting it silently.
> 
> Well, a flavor is always required when launching an instance. I wasn't 
> aware until recently that one could "override" the root GB (or eph/swap) 
> sizes in the API. Apparently, the API allows it, though, even though the 
> code ignores whatever was passed as the override value. If the API 
> supports it, I think the code should probably be changed to override the 
> size values to whatever the user entered, no?

That's the question here. There's a lot of desire to have the overrides
be the values used in scheduling, since currently the flavor values are
used, but making that change potentially impacts how flavors are packed
onto hosts for some deployers. The main thing I want to get out of this
thread is if that's okay.

The sense I get so far is that it's okay to make the change to have bdm
values be passed to the scheduler, via RequestSpec modifications, and
deployers can rely upon CPU/RAM constraints to determine packing. So the
main thing to do is have good release notes about the change.

> 
> -jay
> 
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