Open Stack

my 0.02€ on the matter inline.

Regards,
Salvatore

On 18 August 2015 at 23:45, Mathieu Rohon <mathieu.rohon at gmail.com> wrote:

> hi brandon,
>
> thanks for your answer.
>
> my answers inline,
>
>
>
> On Tue, Aug 18, 2015 at 8:53 PM, Brandon Logan <
> brandon.logan at rackspace.com> wrote:
>
>> ​So let me make sure I understand this. You want to do a separate service
>> plugin for what would normally be separate drivers under one service
>> plugin.  The reasons for this are:
>>
>>
>> 1. You dont want users the ability to choose the type, you want it always
>> to be the same one
>>
> While in theory it is be possible to have multiple BGPVPN providers in the
same deployment, there are control and data plane aspects that the service
type framework at the moment cannot deal with it. Mathieu brought some
examples in the bug report. The bottom line appears to be that the choice
of the l3 service plugin (or whatever serves l3 in your deployment) also
dictates the choiche of the BGPVPN service provider to employ.

> 2. Some types do want to be the source of truth of the data stored,
>> instead of it being the service plugin database.
>>
> This point has little to do with service types. It's about the fact that
plugins are not required to implemented the various db mixins in neutron.db
and therefore not required to use the neutron DB.

>
>> First, let me address the possibility of a solution using one service
>> plugin and multiple drivers per type:
>>
>>
>> I think that you can overcome #1 in the instantiation of the service
>> plugin to check if there are more than 1 provider active, if so you can
>> just throw an exception saying you can only have 1.  I'd have to look at it
>> more to see if there are any caveats to this, but I think that would work.
>>
>>
>> For #2, assuming #1 works, then the drivers that are defined can have
>> some boolean that they set that will tell the plugin whether they are the
>> source of truth or not, and depending on that you can store the data in the
>> service plugin's db or just pass the data along, also pass GET requests to
>> the drivers as well.
>>
>>
> I agree that those workarounds will surely works but I wonder what is the
> meaning of a service plugin/type that can only support one service
> provider? can't the service plugin be the service provider directly?
>

I believe there is some value, but I am not able to quantify it at the
moment.
- A single service plugin also implies (more or less) a common user-facing
APIs. I really don't want to end up in a conditons where the user API looks
different (or the workflow is different) according to what's backing the
neutron BGPVPN implementation
- A single service plugin provides a commonplace for all the boilerplate
management logic. This works for most drivers, but not for those who don't
rely on neutron DB as a data source (unless you manage to build a
sqlalchemy dialect for things such as opencontrail APIs, but I seriously
doubt that it would be feasible)
- Distinct service plugins might lead to different workflows. This is not
necessarily a bad thing, because integration for some backends might need
it. However this means that during review phase particular attention should
be paid to ensure the behaviour of each service plugin respects the API
specification.


>
> The reasons why I'm considering this change are :
>
> 1. I'm not sure we would have some use cases where we would be able to
> choose one bgpvpn backend independently from the provider of the core
> plugin (or a mech driver in the ML2 case) and/or the router plugin.
> If one use ODL to manage its core resources, he won't be able to use nuage
> or contrail to manage its bgpvpn connection.
> The bgpvpn project is more about having a common API than having the
> capacity to mix backends. At least for the moment.
>

I agree with this; but this problem exists regardless of whether you have a
single service plugin with drivers or multiple service plugins. You are
unlikely to be able to use the contrail BGPVPN service plugin is core and
l3 are managed by ODL, I think.


>
> 2. I'm also considering that each plugin, which would be backend
> dependent, could declare what features it supports through the use of
> extensions.
>

Unfortunately extensions are the only way to declare supported capabilities
at the moment. But please - don't end up allowing each service plugin
exposing a different API.


> Each plugin would be a "bgpvpn" service type, and would implement the
> bgpvpn extension, but some of them could extend the bgpvpn_connection
> resource with other extensions also hosted in the bgpvpn project. Since
> some backends only support attachment of networks to a bgpvpn_connection,
> others support attachment of routers, and others both attachments, I'm
> considering having an extension for each type of attachment. Then the
> bgpvpn plugin declares what extensions it supports and the end user can act
> accordingly depending on the scan of neutron extensions.
>

This is not good. It appears that you are forced to leak backend details to
API consumers. Is it possible for you to share more context on why this is
necessary and there's nothing that can be done to avoid it?



> By moving to one plugin per backend, the load of extensions would be done
> by the neutron framework, natively. We won't have to scan each service
> providers to see what extensions it supports, as it is done by the ML2
> extension manager.
> But I agree that with your workaround, of allowing only one service
> provider, we can easily scan this driver for its extensions.
>

Indeed. But still, backends like contrail will have to provide their own
service plugin I think. Which might be ok. All the backends which leverage
the neutron DB might use the "driverized" plugin, and the others can supply
their own service plugin.

>
>
>> As for making a service plugin for each type, I don't see why that
>> wouldn't work.  It seems a bit overkill to me though because you'd probably
>> end up having 2 base classes for every service plugin type, one for using
>> the service plugin database and another for the data source of truth being
>> external.  Probably a better way to do this, I'm sure I'm oversimplifying.
>>
> You're right, and you're not oversimplifying. With this change, the bgpvpn
> framework will only manage API extensions and the DB layer if needed. And
> we don't want this framework to be complicated, in a first step, we just
> want to have a consistent API for every backends.
>
I don't see much technical reasons why you couldn't do this, though.  It's
>> just inconsistent and might cause some confusion.  I'd need to spend some
>> time on it to really have an educated opinion.
>>
> The fact that this change will lead to inconsistency between usage of each
> service plugins is a valid point and might be enough to not do it and
> instead limiting the bgpvpn service plugin to be able to only load one
> service driver for the moment. Which is also inconsistent with some other
> service plugins, but probably less.
>
> thanks brandon.
>
> Mathieu
>
> Thanks,
>> Brandon
>> ------------------------------
>> *From:* Mathieu Rohon <mathieu.rohon at gmail.com>
>> *Sent:* Tuesday, August 18, 2015 7:13 AM
>> *To:* OpenStack Development Mailing List
>> *Subject:* [openstack-dev] [Neutron][bgpvpn] Service Plugin vs Service
>> driver
>>
>> Adding the related subject :)
>>
>> On Tue, Aug 18, 2015 at 10:35 AM, Mathieu Rohon <mathieu.rohon at gmail.com>
>> wrote:
>>
>>> Hi all,
>>>
>>> The current bgpvpn implementation is using the service type framework,
>>> with a service plugin and one or more service providers.
>>>
>>> After registering the bug [1], I wonder if we would rather use a service
>>> plugin per implementation type (bagpipe, ODL, OpenContrail, Nuage...) which
>>> handles API calls, instead of having one service plugin which forwards API
>>> calls to a service driver depending on the provider chosen by the end user.
>>>
>>> I would like to better understand what would be the main drawbacks of
>>> such a move apart from the fact that a deployment would be tightly coupled
>>> to a bgpvpn plugin, and multiple implementations of the plugin couldn't
>>> coexist.
>>>
>>> Thanks,
>>>
>>> Mathieu
>>>
>>> [1]https://bugs.launchpad.net/bgpvpn/+bug/1485515
>>>
>>
>>
>> __________________________________________________________________________
>> 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
>>
>>
>
> __________________________________________________________________________
> 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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstack.org/pipermail/openstack-dev/attachments/20150819/66af75ac/attachment.html>