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On 5/17/2015 1:22 PM, Adrian Otto wrote:
> Good questions Matt and Alex. Currently Magnum creates Bays (places that can run containers, or pods of containers, and other high level resources such as service, replication controllers, etc.) composed of one or more Nova instances (Nodes). This way, we can potentially allow the creation and management for containers on any compute form factor (bare metal, VM, container, etc.). The Nova instances Magnum uses to form the Bays come from Heat.
>
> NOTE: There is no such thing as a nova-magnum virt driver today. The following discussion is theoretical.
>
> Understanding that, it would be possible to make a nova-magnum virt driver that talks to Magnum to ask for an instance of type container from an *existing* Bay, but then Magnum would need to have access to Nova instances that are NOT produced by the nova-magnum driver in order to scale out the Bay by adding more nodes to it. If we do this, and the cloud operator does not realize the circular dependency when setting Nova to use a nova-magnum virt driver, it would be possible to create a loop where nova-magnum provides containers to Magnum that come from the same bay we are attempting to scale out. This would prevent the Bay from actually scaling out because it will be sourcing capacity from itself. We could allow this to work by requiring anyone who uses nova-magnum to also have another Nova host aggregate that uses an alternate virt driver (Ironic, libvirt, etc.), and having some way for Magnum’s Heat template to ask only for instances produced without the Magnum virt driv!
 er when 
forming or scaling Bays. I suppose a scheduling hint might be adequate for this.
>
> Adrian
>
>> On May 17, 2015, at 11:48 AM, Matt Riedemann <mriedem at linux.vnet.ibm.com> wrote:
>>
>>
>>
>> On 5/16/2015 10:52 PM, Alex Glikson wrote:
>>> If system containers is a viable use-case for Nova, and if Magnum is
>>> aiming at both application containers and system containers, would it
>>> make sense to have a new virt driver in nova that would invoke Magnum
>>> API for container provisioning and life cycle? This would avoid (some of
>>> the) code duplication between Magnum and whatever nova virt driver would
>>> support system containers (such as nova-docker). Such an approach would
>>> be conceptually similar to nova virt driver invoking Ironic API,
>>> replacing nova-baremetal (here again, Ironic surfaces various
>>> capabilities which don't make sense in Nova).
>>> We have recently started exploring this direction, and would be glad to
>>> collaborate with folks if this makes sense.
>>>
>>> Regards,
>>> Alex
>>>
>>>
>>> Adrian Otto <adrian.otto at rackspace.com> wrote on 09/05/2015 07:55:47 PM:
>>>
>>>> From: Adrian Otto <adrian.otto at rackspace.com>
>>>> To: "OpenStack Development Mailing List (not for usage questions)"
>>>> <openstack-dev at lists.openstack.org>
>>>> Date: 09/05/2015 07:57 PM
>>>> Subject: Re: [openstack-dev] [nova-docker] Status update
>>>>
>>>> John,
>>>>
>>>> Good questions. Remarks in-line from the Magnum perspective.
>>>>
>>>> On May 9, 2015, at 2:51 AM, John Garbutt <john at johngarbutt.com> wrote:
>>>>
>>>>> On 1 May 2015 at 16:14, Davanum Srinivas <davanum at gmail.com> wrote:
>>>>>> Anyone still interested in this work? :)
>>>>>>
>>>>>> * there's a stable/kilo branch now (see
>>>>>> http://git.openstack.org/cgit/stackforge/nova-docker/).
>>>>>> * CI jobs are running fine against both nova trunk and nova's
>>>>>> stable/kilo branch.
>>>>>> * there's an updated nova-spec to get code back into nova tree (see
>>>>>> https://review.openstack.org/#/c/128753/)
>>>>>
>>>>> To proxy the discussion from the etherpad onto the ML, we need to work
>>>>> out why this lives in nova, given Magnum is the place to do container
>>>>> specific things.
>>>>
>>>> To the extent that users want to control Docker containers through
>>>> the Nova API (without elaborate extensions), I think a stable in-
>>>> tree nova-docker driver makes complete sense for that.
>>>>
>>> [...]
>>>>
>>>>> Now whats the reason for adding the Docker driver, given Nova is
>>>>> considering "container specific" APIs out of scope, and expecting
>>>>> Magnum to own that kind of thing.
>>>>
>>>> I do think nova-docker should find it’s way into the Nova tree. This
>>>> makes containers more accessible in OpenStack, and appropriate for
>>>> use cases where users want to treat containers like they treat
>>>> virtual machines. On the subject of extending the Nova API to
>>>> accommodate special use cases of containers that are beyond the
>>>> scope of the Nova API, I think we should resist that, and focus
>>>> those container-specific efforts in Magnum. That way, cloud
>>>> operators can choose whether to use Nova or Magnum for their
>>>> container use cases depending on the range of features they desire
>>>> from the API. This approach should also result in less overlap of
>>> efforts.
>>>>
>>> [...]
>>>> To sum up, I strongly support merging in nova-docker, with the
>>>> caveat that it operates within the existing Nova API (with few minor
>>>> exceptions). For features that require API features that are truly
>>>> container specific, we should land those in Magnum, and keep the
>>>> Nova API scoped to operations that are appropriate for “all" instance
>>> types.
>>>>
>>>> Adrian
>>>>
>>>>>
>>>>> Thanks,
>>>>> John
>>>>>
>>>
>>>
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>>>
>>
>> I was wondering the exact same thing, why not work on a nova virt driver that talks to the magnum API?
>>
>> --
>>
>> Thanks,
>>
>> Matt Riedemann
>>
>>
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>
>
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OK, ignorance on my part, I didn't realize Magnum was using Nova. I'd 
like to avoid any circular dependencies anywhere at all times. :)

-- 

Thanks,

Matt Riedemann