[openstack-dev] [Neutron] VLAN transparency support

Akihiro Motoki amotoki at gmail.com
Fri Mar 20 06:49:14 UTC 2015


API extension is the only way that users know which features are
available unitl we support API microversioning (v2.1 or something).
I believe VLAN transparency support should be implemented as an
extension, not by changing the core resources attribute directly.
Otherwise users (including Horizon) cannot know we field is available or not.

Even though VLAN transparency and MTU suppotrs are basic features, it
is better to be implemented as an extension.
Configuration does not help from API perspective as it is not visible
through the API.

We are discussing moving away from extension attributes as Armando commented,
but I think it is discussed about resources/attributes which are
already used well and required.
It looks natural to me that new resources/attributes are implemented
via an extension.
The situation may be changed once we have support of API microversioning.
(It is being discussed in the context of Nova API microvesioning in
the dev list started by Jay Pipes.)

In my understanding, the case of IPv6 two mode is an exception.
>From the initial design we would like to have fully support of IPv6 in
subnet resource,
but through the discussion of IPv6 support it turns out some more
modes are required,
and we decided to change the subnet "core" resource. It is the exception.

Thanks,
Akihiro


2015-03-20 7:33 GMT+09:00 Armando M. <armamig at gmail.com>:
> If my memory does not fail me, changes to the API (new resources, new
> resource attributes or new operations allowed to resources) have always been
> done according to these criteria:
>
> an opt-in approach: this means we know the expected behavior of the plugin
> as someone has coded the plugin in such a way that the API change is
> supported;
> an opt-out approach: if the API change does not require explicit backend
> support, and hence can be deemed supported by all plugins.
> a 'core' extension (ones available in neutron/extensions) should be
> implemented at least by the reference implementation;
>
> Now, there might have been examples in the past where criteria were not met,
> but these should be seen as exceptions rather than the rule, and as such,
> fixed as defects so that an attribute/resource/operation that is
> accidentally exposed to a plugin will either be honored as expected or an
> appropriate failure is propagated to the user. Bottom line, the server must
> avoid to fail silently, because failing silently is bad for the user.
>
> Now both features [1] and [2] violated the opt-in criterion above: they
> introduced resources attributes in the core models, forcing an undetermined
> behavior on plugins.
>
> I think that keeping [3,4] as is can lead to a poor user experience; IMO
> it's unacceptable to let a user specify the attribute, and see that
> ultimately the plugin does not support it. I'd be fine if this was an
> accident, but doing this by design is a bit evil. So, I'd suggest the
> following, in order to keep the features in Kilo:
>
> Patches [3, 4] did introduce config flags to control the plugin behavior,
> but it looks like they were not applied correctly; for instance, the
> vlan_transparent case was only applied to ML2. Similarly the MTU config flag
> was not processed server side to ensure that plugins that do not support
> advertisement do not fail silently. This needs to be rectified.
> As for VLAN transparency, we'd need to implement work item 5 (of 6) of spec
> [2], as this extension without at least a backend able to let tagged traffic
> pass doesn't seem right.
> Ensure we sort out the API tests so that we know how the features behave.
>
> Now granted that controlling the API via config flags is not the best
> solution, as this was always handled through the extension mechanism, but
> since we've been talking about moving away from extension attributes with
> [5], it does sound like a reasonable stop-gap solution.
>
> Thoughts?
> Armando
>
> [1]
> http://specs.openstack.org/openstack/neutron-specs/specs/kilo/mtu-selection-and-advertisement.html
> [2]
> http://specs.openstack.org/openstack/neutron-specs/specs/kilo/nfv-vlan-trunks.html
> [3]
> https://review.openstack.org/#/q/project:openstack/neutron+branch:master+topic:bp/mtu-selection-and-advertisement,n,z
> [4]
> https://review.openstack.org/#/q/project:openstack/neutron+branch:master+topic:bp/nfv-vlan-trunks,n,z
> [5] https://review.openstack.org/#/c/136760/
>
> On 19 March 2015 at 12:01, Gary Kotton <gkotton at vmware.com> wrote:
>>
>> With regards to the MTU can you please point me to where we validate that
>> the MTU defined by the tenant is actually <= the supported MTU on the
>> network. I did not see this in the code (maybe I missed something).
>>
>>
>> From: Ian Wells <ijw.ubuntu at cack.org.uk>
>> Reply-To: OpenStack List <openstack-dev at lists.openstack.org>
>> Date: Thursday, March 19, 2015 at 8:44 PM
>> To: OpenStack List <openstack-dev at lists.openstack.org>
>> Subject: Re: [openstack-dev] [Neutron] VLAN transparency support
>>
>> Per the other discussion on attributes, I believe the change walks in
>> historical footsteps and it's a matter of project policy choice.  That
>> aside, you raised a couple of other issues on IRC:
>>
>> - backward compatibility with plugins that haven't adapted their API -
>> this is addressed in the spec, which should have been implemented in the
>> patches (otherwise I will downvote the patch myself) - behaviour should be
>> as before with the additional feature that you can now tell more about what
>> the plugin is thinking
>> - whether they should be core or an extension - this is a more personal
>> opinion, but on the grounds that all networks are either trunks or not, and
>> all networks have MTUs, I think they do want to be core.  I would like to
>> see plugin developers strongly encouraged to consider what they can do on
>> both elements, whereas an extension tends to sideline functionality from
>> view so that plugin writers don't even know it's there for consideration.
>>
>> Aside from that, I'd like to emphasise the value of these patches, so
>> hopefully we can find a way to get them in in some form in this cycle.  I
>> admit I'm interested in them because they make it easier to do NFV.  But
>> they also help normal cloud users and operators, who otherwise have to do
>> some really strange things [1].  I think it's maybe a little unfair to post
>> reversion patches before discussion, particularly when the patch works,
>> passes tests and implements an approved spec correctly.
>> --
>> Ian.
>> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1138958 (admittedly first
>> link I found, but there's no shortage of them)
>>
>> On 19 March 2015 at 05:32, Gary Kotton <gkotton at vmware.com> wrote:
>>>
>>> Hi,
>>> This patch has the same addition too -
>>> https://review.openstack.org/#/c/154921/. We should also revert that one.
>>> Thanks
>>> Gary
>>>
>>> From: Gary Kotton <gkotton at vmware.com>
>>> Reply-To: OpenStack List <openstack-dev at lists.openstack.org>
>>> Date: Thursday, March 19, 2015 at 1:14 PM
>>> To: OpenStack List <openstack-dev at lists.openstack.org>
>>> Subject: [openstack-dev] [Neutron] VLAN transparency support
>>>
>>> Hi,
>>> It appears that https://review.openstack.org/#/c/158420/ update the base
>>> attributes for the networks. Is there any reason why this was not added as a
>>> separate extension like all others.
>>> I do not think that this is the correct way to go and we should do this
>>> as all other extensions have been maintained. I have posted a revert
>>> (https://review.openstack.org/#/c/165776/) - please feel free to knack if it
>>> is invalid.
>>> Thanks
>>> Gary
>>>
>>>
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-- 
Akihiro Motoki <amotoki at gmail.com>



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