[openstack-dev] Custom Flavor creation through Heat

Shawn Hartsock hartsocks at vmware.com
Tue Nov 12 23:38:21 UTC 2013

----- Original Message -----
> From: "Yunhong Jiang" <yunhong.jiang at intel.com>
> To: "OpenStack Development Mailing List (not for usage questions)" <openstack-dev at lists.openstack.org>
> Sent: Tuesday, November 12, 2013 5:39:58 PM
> Subject: Re: [openstack-dev] Custom Flavor creation through Heat
> > -----Original Message-----
> > From: Shawn Hartsock [mailto:hartsocks at vmware.com]
> > Sent: Tuesday, November 12, 2013 12:56 PM
> > To: OpenStack Development Mailing List (not for usage questions)
> > Subject: Re: [openstack-dev] [nova] [heat] Custom Flavor creation through
> > Heat
> > 
> > My concern with proliferating custom flavors is that it might play havoc
> > with the underlying root-case for flavors.
> > 
> > My understanding of flavors is that they are used to solve the resource
> > packing problem in elastic cloud scenarios. That way you know that 256
> > "tiny" VMs fit cleanly into your hardware layout and so do 128 "medium"
> > VMs and 64 large VMs. If you allow "flavor of the week" then the packing
> > problem re-asserts itself and scheduling becomes harder.
> I'm a bit surprised that the flavor is used to resolve the packing problem. I
> thought it should be handled by scheduler, although it's a NP problem.

I should have said "flavors help to make the packing problem simpler for the scheduler" ... flavors do not "solve" the packing problem.

> As for custom flavor, I think at least it's against current nova assumption.
> Currently nova assume flavor should only be created by admin, who knows the
> cloud quite well.
> One example is, flavor may contain extra-spec, so if an extra-spec value is
> specified in the flavor, while the corresponding scheduler filter is not
> enabled, then the extra-spec has no effect and may cause issue.

Beyond merely extra-specs my understanding was that because you *have* flavors you can make assumptions about packing that make the problem space smaller... someone made a nice presentation showing how having restricted flavors made scheduling easier. I can't find it right now. It was presented at an OpenStack summit IIRC

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