[openstack-dev] [nova][cinder] Fix nova swap volume (updating an attached volume) function

Matt Riedemann mriedem at linux.vnet.ibm.com
Thu Mar 31 02:29:00 UTC 2016



On 3/30/2016 9:14 PM, GHANSHYAM MANN wrote:
> On Thu, Mar 31, 2016 at 10:39 AM, Matt Riedemann
> <mriedem at linux.vnet.ibm.com> wrote:
>>
>>
>> On 3/30/2016 8:20 PM, Matt Riedemann wrote:
>>>
>>>
>>>
>>> On 3/30/2016 7:56 PM, Matt Riedemann wrote:
>>>>
>>>>
>>>>
>>>> On 3/30/2016 7:38 PM, Matt Riedemann wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2/25/2016 5:31 AM, Takashi Natsume wrote:
>>>>>>
>>>>>> Hi Nova and Cinder developers.
>>>>>>
>>>>>> As I reported in a bug report [1], nova swap volume
>>>>>> (updating an attached volume) fuction does not work
>>>>>> in the case of non admin users by default.
>>>>>> (Volumes are stuck.)
>>>>>>
>>>>>> Before I was working for fixing another swap volume bug [2][3].
>>>>>> But Ryan fixed it on the Cinder side [4].
>>>>>> As a result, admin users can execute swap volume function,
>>>>>> but it was not fixed in the case of non admin users.
>>>>>> So I reported the bug report [1].
>>>>>>
>>>>>> In the patch[5], I tried to change the default cinder's policy
>>>>>> to allow non admin users to execute migrate_volume_completion API.
>>>>>> But it was rejected by the cinder project ('-2' was voted).
>>>>>>
>>>>>> In the patch[5], it was suggested to make the swap volume API admin
>>>>>> only
>>>>>> on the Nova side.
>>>>>> But IMO, the swap volume function should be allowed to non admin users
>>>>>> because attaching a volume and detaching a volume can be performed
>>>>>> by non admin users.
>>>>>
>>>>>
>>>>> I agree with this. DuncanT said in IRC that he didn't think non-admin
>>>>> users should be using the swap-volume API in nova because it can be
>>>>> problematic, but I'm not sure why, is there more history or detail
>>>>> there? I'd think it shouldn't be any worse than doing a detach/attach in
>>>>> quick succession (like in a CI test for example).
>>>>>
>>>>>>
>>>>>> If migrate_volume_completion is only allowed to admin users
>>>>>> by default on the Cinder side, attaching a new volume and
>>>>>> detaching an old volume should be performed on the Nova side
>>>>>> when swapping volumes.
>>>>>
>>>>>
>>>>> My understanding of the problem is as follows:
>>>>>
>>>>> 1. Admin-initiated volume migration in Cinder calls off to Nova to
>>>>> perform the swap-volume, and then Nova calls back to Cinder's
>>>>> migrate_volume_completion API. This is fine since it's an admin that
>>>>> initiated this series of operations on the Cinder side (that's by
>>>>> default, however, this is broken if the policy file for Cinder is change
>>>>> to allow non-admins to migrate volumes).
>>>>>
>>>>> 2. A non-admin swap-volume API call in Nova fails because Nova blindly
>>>>> makes the migrate_volume_completion call to Cinder which fails with a
>>>>> 403 because the Cinder API policy has that as an admin action by
>>>>> default.
>>>>>
>>>>> I don't know the history around when the swap-volume API was added to
>>>>> Nova, was it specifically for this volume migration scenario in Cinder?
>>>>>    Are there other use cases?  Knowing those would be good to determine
>>>>> if Nova should change it's default policy for swap-volume, although,
>>>>> again, that's only a default and can be changed per deployment so we
>>>>> probably shouldn't rely on it.
>>>>>
>>>>> Ideally we would have implemented this like the nova/neutron server
>>>>> events callback API in Nova during vif plugging (nova does the vif plug
>>>>> on the host then waits for neutron to update it's database for the port
>>>>> status and sends an event (API call) to nova to continue booting the
>>>>> server). That server events API in nova is admin-only by default and
>>>>> neutron is configured with admin credentials for nova to use it.
>>>>>
>>>>> Another option would be for Nova to handle a 403 response when calling
>>>>> Cinder's migrate_volume_completion API and ignore it if we don't have an
>>>>> admin context. This is pretty hacky though. It assumes that it's a
>>>>> non-admin user initiating the swap-volume operation. It wouldn't be a
>>>>> problem for the volume migration operation initiated in Cinder since by
>>>>> default that's admin-only, so nova shouldn't get a 403 when calling
>>>>> migrate_volume_completion. The trap would be if the cinder policy for
>>>>> volume migration was changed to allow non-admins, but if someone did
>>>>> that, they should also change the policy for migrate_volume_completion
>>>>> to allow non-admin too.
>>>>>
>>>>>>
>>>>>> If you have a good idea, please let me know it.
>>>>>>
>>>>>> [1] Cinder volumes are stuck when non admin user executes nova swap
>>>>>> volume API
>>>>>>       https://bugs.launchpad.net/cinder/+bug/1522705
>>>>>>
>>>>>> [2] Cinder volume stuck in swap_volume
>>>>>>       https://bugs.launchpad.net/nova/+bug/1471098
>>>>>>
>>>>>> [3] Fix cinder volume stuck in swap_volume
>>>>>>       https://review.openstack.org/#/c/207385/
>>>>>>
>>>>>> [4] Fix swap_volume for case without migration
>>>>>>       https://review.openstack.org/#/c/247767/
>>>>>>
>>>>>> [5] Enable volume owners to execute migrate_volume_completion
>>>>>>       https://review.openstack.org/#/c/253363/
>>>>>>
>>>>>> Regards,
>>>>>> Takashi Natsume
>>>>>> NTT Software Innovation Center
>>>>>> E-mail: natsume.takashi at lab.ntt.co.jp
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> __________________________________________________________________________
>>>>>>
>>>>>>
>>>>>>
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>>>>>>
>>>>>
>>>>
>>>> I also just checked Tempest and apparently we have no coverage for the
>>>> swap-volume API in Nova, we should fix that as part of this.
>>>>
>>>
>>> I've done some more digging. The swap-volume functionality was added to
>>> nova here [1].  The cinder use of it for volume migration was added here
>>> [2].
>>>
>>> Looking at the cinder volume API for migrate_volume_completion, it
>>> expects the source (old) volume to have migration_status set [3].
>>>
>>> So, I think we can easily fix this in Nova by simply not calling
>>> volume_migration_completion if old_volume['migration_status'] is None.
>>>
>>> [1]
>>>
>>> https://github.com/openstack/nova/commit/8f51b120b430c7c21399256f37e1d8f75d030484
>>>
>>> [2]
>>>
>>> https://github.com/openstack/nova/commit/0e4bd7f93b9bfadcc2bb6dfaeae7bb5ee00c194b
>>>
>>> [3]
>>>
>>> http://git.openstack.org/cgit/openstack/cinder/tree/cinder/volume/api.py#n1358
>>>
>>>
>>
>> Of course that had to be too easy to be true. The volume 'migration_status'
>> is only returned for the volume details if you're calling with an admin
>> context [1].
>>
>> I think we can still use this, we just can't expect
>> volume['migration_status'] to be in the response from the volume GET. If
>> it's not there, we can assume we're not doing a migration and we're not an
>> admin anyway, so we can't call migrate_volume_completion.
>
> So in that case, we need to attach, detach volume on nova side right?
> I mean if migrate_volume_completion is not being called then
> new volume attachment and old volume detachment should be initiated explicitly.
>
> Can we make Nova default policy same as cinder, i mean swap volume
> allowed only for admin? Because if there is simple swap initiated from
> nova(not cinder migration), Nova allow that operation for non-admin
> user and get stuck to attaching/detaching status.
>
>>
>> [1]
>> http://git.openstack.org/cgit/openstack/cinder/tree/cinder/api/v2/views/volumes.py#n82-L84
>>
>> --
>>
>> Thanks,
>>
>> Matt Riedemann
>>
>>
>> __________________________________________________________________________
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>
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>

Good question, I'm assuming the virt driver does the attach/detach on 
the nova side, but I haven't dug into it or verified the fix myself. I 
wanted to write a Tempest test for the non-admin swap-volume case in Nova.

Changing the nova policy to be admin-only by default for swap-volume was 
another easy option, I just wasn't sure if it was the right thing to do 
since this was not initially added as an admin-only operation, and it 
seems the only thing that's made it become that is the cinder volume 
migration callback case.

-- 

Thanks,

Matt Riedemann




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