[openstack-dev] [neutron] L2 gateway as a service

Armando M. armamig at gmail.com
Wed Nov 19 02:44:06 UTC 2014


On 18 November 2014 16:22, Ian Wells <ijw.ubuntu at cack.org.uk> wrote:

> Sorry I'm a bit late to this, but that's what you get from being on
> holiday...  (Which is also why there are no new MTU and VLAN specs yet, but
> I swear I'll get to them.)

Ah! I hope it was good at least :)

> On 17 November 2014 01:13, Mathieu Rohon <mathieu.rohon at gmail.com> wrote:
>> Hi
>> On Fri, Nov 14, 2014 at 6:26 PM, Armando M. <armamig at gmail.com> wrote:
>> > Last Friday I recall we had two discussions around this topic. One in
>> the
>> > morning, which I think led to Maruti to push [1]. The way I understood
>> [1]
>> > was that it is an attempt at unifying [2] and [3], by choosing the API
>> > approach of one and the architectural approach of the other.
>> >
>> > [1] https://review.openstack.org/#/c/134179/
>> > [2] https://review.openstack.org/#/c/100278/
>> > [3] https://review.openstack.org/#/c/93613/
>> >
>> > Then there was another discussion in the afternoon, but I am not 100%
>> of the
>> > outcome.
>> Me neither, that's why I'd like ian, who led this discussion, to sum
>> up the outcome from its point of view.
> So, the gist of what I said is that we have three, independent, use cases:
> - connecting two VMs that like to tag packets to each other (VLAN clean
> networks)
> - connecting many networks to a single VM (trunking ports)
> - connecting the outside world to a set of virtual networks
> We're discussing that last use case here.  The point I was made was that:
> - there are more encaps in the world than just VLANs
> - they can all be solved in the same way using an edge API

No disagreement all the way up to this point, assumed that I don't worry
about what this edge API really is.

> - if they are solved using an edge API, the job of describing the network
> you're trying to bring in (be it switch/port/vlan, or MPLS label stack, or
> l2tpv3 endpoint data) is best kept outside of Neutron's API, because
> Neutron can't usefully do anything with it other than validate it and hand
> it off to whatever network control code is being used.  (Note that most
> encaps will likely *not* be implemented in Neutron's inbuilt control code.)

This is where the disagreement begins, as far as I am concerned; in fact we
already have a well defined way of describing what a network entity in
Neutron is, namely an L2 broadcast domain abstraction. An L2 gateway API
that is well defined and well scoped should just express how one can be
connected to another, nothing more, at least as a starting point.

> Now, the above argument says that we should keep this out of Neutron.  The
> problem with that is that people are using the OVS mechanism driver and
> would like a solution that works with that, implying something that's
> *inside* Neutron.  For that case, it's certainly valid to consider another
> means of implementation, but it wouldn't be my personal choice.  (For what
> it's worth I'm looking at ODL based controller implementations, so this
> isn't an issue for me personally.)
> If one were to implement the code in the Neutron API, even as an
> extension, I would question whether it's a sensible thing to attempt before
> the RPC server/REST server split is done, since it also extends the API
> between them.
> > All this churn makes me believe that we probably just need to stop
>> > pretending we can achieve any sort of consensus on the approach and let
>> the
>> > different alternatives develop independently, assumed they can all
>> develop
>> > independently, and then let natural evolution take its course :)
>> I tend to agree, but I think that one of the reason why we are looking
>> for a consensus, is because API evolutions proposed through
>> Neutron-spec are rejected by core-dev, because they rely on external
>> components (sdn controller, proprietary hardware...) or they are not a
>> high priority for neutron core-dev.
>> By finding a consensus, we show that several players are interested in
>> such an API, and it helps to convince core-dev that this use-case, and
>> its API, is missing in neutron.
> There are lots of players interested in an API, that much is clear, and
> all the more so if you consider that this feature has strong analogies with
> use cases such as switch port exposure and MPLS.  The problem is that it's
> clearly a fairly complex API with some variety of ways to implement it, and
> both of these things work against its acceptance.  Additionally, per the
> above discussion, I would say it's not essential for it to be core Neutron
> functionality.

> Now, if there is room for easily propose new API in Neutron, It make
>> sense to leave new API appear and evolve, and then " let natural
>> evolution take its course ", as you said.
> Natural selection works poorly on APIs because once they exist they're
> hard to change and/or retire, due to backward compatibility requirements.

Well, that is true assumed that someone can or is willing to use them :)

>> To me, this is in the scope of the "advanced services" project.
> Advanced services or no, the point I was making is that this is not
> something that should fit under the Neutron API endpoint.  Since it's not
> really related to any of the other advanced services it's not particularly
> necessary that it fit under the Advanced Services API endpoint either,
> although it could.  My Unix design leanings say to me that if things are
> not related they shouldn't be combined, though - the simplest thing that
> does the job is the right answer.
> --
> Ian.
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