On 09/23/15 at 02:55pm, Matt Riedemann wrote:
On 9/23/2015 2:45 PM, John Griffith wrote:
On Wed, Sep 23, 2015 at 1:34 PM, Matt Riedemann
<[email protected] <mailto:[email protected]>> wrote:
On 9/23/2015 2:15 PM, Matt Riedemann wrote:
On 9/23/2015 1:46 PM, Ivan Kolodyazhny wrote:
Hi Matt,
In Liberty, we introduced allow_availability_zone_fallback
[1] option in
Cinder config as fix for bug [2]. If you set this option,
Cinder will
create volume in a default AZ instead of set volume into the
error state
[1]
https://github.com/openstack/cinder/commit/b85d2812a8256ff82934d150dbc4909e041d8b31
[2] https://bugs.launchpad.net/cinder/+bug/1489575
Regards,
Ivan Kolodyazhny
On Wed, Sep 23, 2015 at 9:00 PM, Matt Riedemann
<[email protected]
<mailto:[email protected]>
<mailto:[email protected]
<mailto:[email protected]>>> wrote:
I came across bug 1496235 [1] today. In this case the
user is
booting an instance from a volume using source=image,
so nova
actually does the volume create call to the volume
API. They are
booting the instance into a valid nova availability
zone, but that
same AZ isn't defined in Cinder, so the volume create
request fails
(since nova passes the instance AZ to cinder [2]).
I marked this as invalid given how the code works.
I'm posting here since I'm wondering if there are
alternatives worth
pursuing. For example, nova could get the list of AZs
from the
volume API and if the nova AZ isn't in that list, don't
provide it
on the volume create request. That's essentially the
same as first
creating the volume outside of nova and not specifying
an AZ, then
when doing the boot from volume, provide the volume_id
as the source.
The question is, is it worth doing that? I'm not
familiar enough
with how availability zones are meant to work between
nova and
cinder so it's hard for me to have much of an opinion here.
[1] https://bugs.launchpad.net/nova/+bug/1496235
[2]
https://github.com/openstack/nova/blob/master/nova/virt/block_device.py#L381-L383
--
Thanks,
Matt Riedemann
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Sorry but that seems like a hack.
I'm trying to figure out the relationship between AZs in nova
and cinder
and so far no one seems to really know. In the cinder IRC
channel I was
told there isn't one, which would mean we shouldn't even try
creating
the volume using the server instance AZ.
Also, if there is no relationship, I was trying to figure out
why there
is the cinder.cross_az_attach config option. That was added in
grizzly
[1]. I was thinking maybe it was a legacy artifact from
nova-volume,
but that was dropped in grizzly.
So is cinder.cross_az_attach even useful?
[1] https://review.openstack.org/#/c/21672/
The plot thickens.
I was checking to see what change was made to start passing the
server instance az on the volume create call during boot from
volume, and that was [1] which was added in kilo to fix a bug where
boot from volume into a nova az will fail if
cinder.cross_az_attach=False and storage_availability_zone is set in
cinder.conf.
So I guess we can't just stop passing the instance az to the volume
create call.
But what I'd really like to know is how this is all used between
cinder and nova, or was this all some work done as part of a larger
effort that was never completed? Basically, can we deprecate the
cinder.cross_az_attach config option in nova and start decoupling
this code?
[1] https://review.openstack.org/#/c/157041/
--
Thanks,
Matt Riedemann
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To be honest this is probably my fault, AZ's were pulled in as part of
the nova-volume migration to Cinder and just sort of died. Quite
frankly I wasn't sure "what" to do with them but brought over the
concept and the zones that existing in Nova-Volume. It's been an issue
since day 1 of Cinder, and as you note there are little hacks here and
there over the years to do different things.
I think your question about whether they should be there at all or not
is a good one. We have had some interest from folks lately that want to
couple Nova and Cinder AZ's (I'm really not sure of any details or
use-cases here).
My opinion would be until somebody proposes a clear use case and need
that actually works that we consider deprecating it.
While we're on the subject (kinda) I've never been a very fond of having
Nova create the volume during boot process either; there's a number of
things that go wrong here (timeouts almost guaranteed for a "real"
image) and some things that are missing last I looked like type
selection etc.
We do have a proposal to talk about this at the Summit, so maybe we'll
have a descent primer before we get there :)
Thanks,
John
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Heh, so when I just asked in the cinder channel if we can just
deprecate nova boot from volume with source=(image|snapshot|blank)
(which automatically creates the volume and polls for it to be
available) and then add a microversion that doesn't allow it, I was
half joking, but I see we're on the same page. This scenario seems
to introduce a lot of orchestration work that nova shouldn't
necessarily be in the business of handling.
I am very much in support of this. This has been a source of
frustration for our users because it is prone to failures we can't
properly expose to users and timeouts. There are much better places to
handle the orchestration of creating a volume and then booting from it
than Nova.
--
Thanks,
Matt Riedemann
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