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On 24 May 2014 05:20, Robert Kukura <kukura at noironetworks.com> wrote:
>
> On 5/23/14, 10:54 PM, Armando M. wrote:
>>
>> On 23 May 2014 12:31, Robert Kukura <kukura at noironetworks.com> wrote:
>>>
>>> On 5/23/14, 12:46 AM, Mandeep Dhami wrote:
>>>
>>> Hi Armando:
>>>
>>> Those are good points. I will let Bob Kukura chime in on the specifics of
>>> how we intend to do that integration. But if what you see in the
>>> prototype/PoC was our final design for integration with Neutron core, I
>>> would be worried about that too. That specific part of the code
>>> (events/notifications for DHCP) was done in that way just for the
>>> prototype
>>> - to allow us to experiment with the part that was new and needed
>>> experimentation, the APIs and the model.
>>>
>>> That is the exact reason that we did not initially check the code to
>>> gerrit
>>> - so that we do not confuse the review process with the prototype
>>> process.
>>> But we were requested by other cores to check in even the prototype code
>>> as
>>> WIP patches to allow for review of the API parts. That can unfortunately
>>> create this very misunderstanding. For the review, I would recommend not
>>> the
>>> WIP patches, as they contain the prototype parts as well, but just the
>>> final
>>> patches that are not marked WIP. If you such issues in that part of the
>>> code, please DO raise that as that would be code that we intend to
>>> upstream.
>>>
>>> I believe Bob did discuss the specifics of this integration issue with
>>> you
>>> at the summit, but like I said it is best if he represents that side
>>> himself.
>>>
>>> Armando and Mandeep,
>>>
>>> Right, we do need a workable solution for the GBP driver to invoke
>>> neutron
>>> API operations, and this came up at the summit.
>>>
>>> We started out in the PoC directly calling the plugin, as is currently
>>> done
>>> when creating ports for agents. But this is not sufficient because the
>>> DHCP
>>> notifications, and I think the nova notifications, are needed for VM
>>> ports.
>>> We also really should be generating the other notifications, enforcing
>>> quotas, etc. for the neutron resources.
>>
>> I am at loss here: if you say that you couldn't fit at the plugin
>> level, that is because it is the wrong level!! Sitting above it and
>> redo all the glue code around it to add DHCP notifications etc
>> continues the bad practice within the Neutron codebase where there is
>> not a good separation of concerns: for instance everything is cobbled
>> together like the DB and plugin logic. I appreciate that some design
>> decisions have been made in the past, but there's no good reason for a
>> nice new feature like GP to continue this bad practice; this is why I
>> feel strongly about the current approach being taken.
>
> Armando, I am agreeing with you! The code you saw was a proof-of-concept
> implementation intended as a learning exercise, not something intended to be
> merged as-is to the neutron code base. The approach for invoking resources
> from the driver(s) will be revisited before the driver code is submitted for
> review.
>>
>>
>>> We could just use python-neutronclient, but I think we'd prefer to avoid
>>> the
>>> overhead. The neutron project already depends on python-neutronclient for
>>> some tests, the debug facility, and the metaplugin, so in retrospect, we
>>> could have easily used it in the PoC.
>>
>> I am not sure I understand what overhead you mean here. Could you
>> clarify? Actually looking at the code, I see a mind boggling set of
>> interactions going back and forth between the GP plugin, the policy
>> driver manager, the mapping driver and the core plugin: they are all
>> entangled together. For instance, when creating an endpoint the GP
>> plugin ends up calling the mapping driver that in turns ends up calls
>> the GP plugin itself! If this is not overhead I don't know what is!
>> The way the code has been structured makes it very difficult to read,
>> let alone maintain and extend with other policy mappers. The ML2-like
>> nature of the approach taken might work well in the context of core
>> plugin, mechanisms drivers etc, but I would argue that it poorly
>> applies to the context of GP.
>
> The overhead of using python-neutronclient is that unnecessary
> serialization/deserialization are performed as well as socket communication
> through the kernel. This is all required between processes, but not within a
> single process. A well-defined and efficient mechanism to invoke resource
> APIs within the process, with the same semantics as incoming REST calls,
> seems like a generally useful addition to neutron. I'm hopeful the core
> refactoring effort will provide this (and am willing to help make sure it
> does), but we need something we can use until that is available.
>

I appreciate that there is a cost involved in relying on distributed
communication, but this must be negligible considered what needs to
happen end-to-end. If the overhead being referred here is the price to
pay for having a more dependable system (e.g. because things can be
scaled out and/or made reliable independently), then I think this is a
price worth paying.

I do hope that the core refactoring is not aiming at what you're
suggesting, as it sounds in exact opposition to some of the OpenStack
design principles.

> One lesson we learned from the PoC is that the implicit management of the GP
> resources (RDs and BDs) is completely independent from the mapping of GP
> resources to neutron resources. We discussed this at the last GP sub-team
> IRC meeting, and decided to package this functionality as a separate driver
> that is invoked prior to the mapping_driver, and can also be used in
> conjunction with other GP back-end drivers. I think this will help improve
> the structure and readability of the code, and it also shows the
> applicability of the ML2-like nature of the driver API.
>
> You are certainly justified in raising the question of whether the ML2
> driver API model is appropriate for the GP plugin. I raised two issues with
> this in the sub-team's PoC post-mortem discussion. One was whether calling
> multiple drivers is useful. The case above seems to justify this, as well as
> potentially supporting heterogeneous deployments involving multiple ways to
> enforce policy. The other was whether the precommit() methods are useful. I
> think the jury is still out on this.
>>
>>
>>> With the existing REST code, if we could find the
>>> neutron.api.v2.base.Controller class instance for each resource, we could
>>> simply call create(), update(), delete(), and show() on these. I didn't
>>> see
>>> an easy way to find these Controller instances, so I threw together some
>>> code similar to these Controller methods for the PoC. It probably
>>> wouldn't
>>> take too much work to have neutron.manager.NeutronManager provide access
>>> to
>>> the Controller classes if we want to go this route.
>>>
>>> The core refactoring effort may eventually provide a nice solution, but
>>> we
>>> can't wait for this. It seems we'll need to either use
>>> python-neutronclient
>>> or get access to the Controller classes in the meantime.
>>>
>>> Any thoughts on these? Any other ideas?
>>
>> I am still not sure why do you even need to go all the way down to the
>> Controller class. After all it's almost like GP could be a service in
>> its own right that makes use of Neutron to map the application centric
>> abstractions on top of the networking constructs; this can happen via
>> the REST interface. I don't think there is a dependency on the core
>> refactoring here: the two can progress separately, so long as we break
>> the tie, from an implementation perspective, that GP and Core plugins
>> need to leave in the same address space. Am I missing something?
>> Because I still cannot justify why things have been coded the way they
>> have.
>
> I completely agree that we should try to avoid a hard architectural
> requirement that the GP and core plugins have to be in the same address
> space, and agree that if we were to use separate address spaces, using
> python-neutronclient would be the obvious solution. Certain back-end drivers
> for the GP plugin may be more tightly coupled with corresponding core
> plugins or ML2 mechanism drivers, with both cooperating to control the same
> underlying fabric, so we don't want to preclude putting them in the same
> address space either.

I don't believe that the two living in the same address space is a
*must-have* requirement to achieve the tight coupling you think it's
needed, but I appreciate that some things would need to change in
order to make the two to cooperate more closely if they were to exist
separately.

>
> In the PoC, I attempted to structure things so we could easily change the
> mechanism used for these calls. I can't really justify why we didn't just
> use python-neutronclient for the PoC, but remember, it was just a prototype
> intended for learning and to facilitate these sorts of discussions.
>
> So, as long as we do plan to package GP as a service plugin within
> neutron-server, is the overhead of going through python-neutronclient within
> that process acceptable? Are there any other issues with this? If its
> workable, I think we can go with python-neutronclient for now, and look at
> better alternatives as the core refactoring progresses.

I was suggesting to move away from the service plugin model
altogether, but it's certainly something that could be explored in the
short term, if you think this is something you're more comfortable
with; I personally feel that it is going to be detrimental to the GP
efforts because at some point down the road things will need to be
re-architected radically, and I was taking this discussion as an
opportunity to advocate change from the start.

Thanks for clarifying some of my doubts!
Cheers,
Armando

>
> Thanks,
>
> -Bob
>
>>
>> Thanks,
>> Armando
>>
>>> Thanks,
>>>
>>> -Bob
>>>
>>>
>>> Regards,
>>> Mandeep
>>>
>>>
>>>
>>>
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