Open Stack

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
>> <mriedem at linux.vnet.ibm.com <mailto:mriedem at linux.vnet.ibm.com>> 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
>>
>>
>>
>> __________________________________________________________________________
>>
>>     OpenStack Development Mailing List (not for usage questions)
>>     Unsubscribe:
>>     OpenStack-dev-request at lists.openstack.org?subject:unsubscribe
>>
>> <http://OpenStack-dev-request@lists.openstack.org?subject:unsubscribe>
>>     http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>>
>>
>>
>>
>> __________________________________________________________________________
>>
>> OpenStack Development Mailing List (not for usage questions)
>> Unsubscribe:
>> OpenStack-dev-request at lists.openstack.org?subject:unsubscribe
>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
>>
>
> 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