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Jay Pipes <jaypipes at gmail.com> 于2018年10月5日周五 下午9:25写道：

> Added [ironic] topic.
>
> On 10/04/2018 06:06 PM, Chris Friesen wrote:
> > While discussing the "Add HPET timer support for x86 guests"
> > blueprint[1] one of the items that came up was how to represent what are
> > essentially flags that impact both scheduling and configuration.  Eric
> > Fried posted a spec to start a discussion[2], and a number of nova
> > developers met on a hangout to hash it out.  This is the result.
> >
> > In this specific scenario the goal was to allow the user to specify that
> > their image required a virtual HPET.  For efficient scheduling we wanted
> > this to map to a placement trait, and the virt driver also needed to
> > enable the feature when booting the instance.  (This can be generalized
> > to other similar problems, including how to specify scheduling and
> > configuration information for Ironic.)
> >
> > We discussed two primary approaches:
> >
> > The first approach was to specify an arbitrary "key=val" in flavor
> > extra-specs or image properties, which nova would automatically
> > translate into the appropriate placement trait before passing it to
> > placement.  Once scheduled to a compute node, the virt driver would look
> > for "key=val" in the flavor/image to determine how to proceed.
> >
> > The second approach was to directly specify the placement trait in the
> > flavor extra-specs or image properties.  Once scheduled to a compute
> > node, the virt driver would look for the placement trait in the
> > flavor/image to determine how to proceed.
> >
> > Ultimately, the decision was made to go with the second approach.  The
> > result is that it is officially acceptable for virt drivers to key off
> > placement traits specified in the image/flavor in order to turn on/off
> > configuration options for the instance.  If we do get down to the virt
> > driver and the trait is set, and the driver for whatever reason
> > determines it's not capable of flipping the switch, it should fail.
>
> Ironicers, pay attention to the above! :) It's a green light from Nova
> to use the traits list contained in the flavor extra specs and image
> metadata when (pre-)configuring an instance.
>
> > It should be noted that it only makes sense to use placement traits for
> > things that affect scheduling.  If it doesn't affect scheduling, then it
> > can be stored in the flavor extra-specs or image properties separate
> > from the placement traits.  Also, this approach only makes sense for
> > simple booleans.  Anything requiring more complex configuration will
> > likely need additional extra-spec and/or config and/or unicorn dust.
>
> Ironicers, also pay close attention to the advice above. Things that are
> not "scheduleable" -- in other words, things that don't filter the list
> of hosts that a workload can land on -- should not go in traits.
>

++, see I talk about the same thing before
https://review.openstack.org/#/c/504952/5/specs/approved/config-template-traits.rst@95
:)

>
> Finally, here's the HPET os-traits patch. Reviews welcome (it's tiny
> patch):
>
> https://review.openstack.org/608258
>
> Best,
> -jay
>
> > Chris
> >
> > [1] https://blueprints.launchpad.net/nova/+spec/support-hpet-on-guest
> > [2]
> >
> https://review.openstack.org/#/c/607989/1/specs/stein/approved/support-hpet-on-guest.rst
> >
> >
> >
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