[openstack-dev] [neutron] ML2 versus core plugin for OVN
Robert Kukura
kukura at noironetworks.com
Tue Feb 24 16:48:28 UTC 2015
Kyle, What happened to the long-term potential goal of ML2 driver APIs
becoming neutron's core APIs? Do we really want to encourage new
monolithic plugins?
ML2 is not a control plane - its really just an integration point for
control planes. Although co-existence of multiple mechanism drivers is
possible, and sometimes very useful, the single-driver case is fully
supported. Even with hierarchical bindings, its not really ML2 that
controls what happens - its the drivers within the framework. I don't
think ML2 really limits what drivers can do, as long as a virtual
network can be described as a set of static and possibly dynamic network
segments. ML2 is intended to impose as few constraints on drivers as
possible.
My recommendation would be to implement an ML2 mechanism driver for OVN,
along with any needed new type drivers or extension drivers. I believe
this will result in a lot less new code to write and maintain.
Also, keep in mind that even if multiple driver co-existence doesn't
sound immediately useful, there are several potential use cases to
consider. One is that it allows new technology to be introduced into an
existing cloud alongside what previously existed. Migration from one ML2
driver to another may be a lot simpler (and/or flexible) than migration
from one plugin to another. Another is that additional drivers can
support special cases, such as bare metal, appliances, etc..
-Bob
On 2/24/15 11:11 AM, Kyle Mestery wrote:
> On Tue, Feb 24, 2015 at 3:19 AM, Salvatore Orlando
> <sorlando at nicira.com <mailto:sorlando at nicira.com>> wrote:
>
> On 24 February 2015 at 01:34, Kyle Mestery <mestery at mestery.com
> <mailto:mestery at mestery.com>> wrote:
>
> Russel and I have already merged the initial ML2 skeleton
> driver [1].
>
> The thinking is that we can always revert to a non-ML2 driver
> if needed.
>
>
> If nothing else an authoritative decision on a design direction
> saves us the hassle of going through iterations and discussions.
> The integration through ML2 is definitely viable. My opinion
> however is that since OVN implements a full control plane, the
> control plane bits provided by ML2 are not necessary, and a plugin
> which provides only management layer capabilities might be the
> best solution. Note: this does not mean it has to be monolithic.
> We can still do L3 with a service plugin.
> However, since the same kind of approach has been adopted for ODL
> I guess this provides some sort of validation.
>
> To be honest, after thinking about this last night, I'm now leaning
> towards doing this as a full plugin. I don't really envision OVN
> running with other plugins, as OVN is implementing it's own control
> plane, as you say. So the value of using ML2 is quesitonable.
>
> I'm not sure how useful having using OVN with other drivers
> will be, and that was my initial concern with doing ML2 vs.
> full plugin. With the HW VTEP support in OVN+OVS, you can tie
> in physical devices this way. Anyways, this is where we're at
> for now. Comments welcome, of course.
>
>
> That was also kind of my point regarding the control plane bits
> provided by ML2 which OVN does not need. Still, the fact that we
> do not use a function does not make any harm.
> Also i'm not sure if OVN needs at all a type manager. If not, we
> can always implement a no-op type manager, I guess.
>
> See above. I'd like to propose we move OVN to a full plugin instead of
> an ML2 MechanismDriver.
>
> Kyle
>
> Salvatore
>
>
> Thanks,
> Kyle
>
> [1] https://github.com/stackforge/networking-ovn
>
> On Mon, Feb 23, 2015 at 4:09 PM, Kevin Benton
> <blak111 at gmail.com <mailto:blak111 at gmail.com>> wrote:
>
> I want to emphasize Salvatore's last two points a bit
> more. If you go with a monolithic plugin, you eliminate
> the possibility of heterogenous deployments.
>
> One example of this that is common now is having the
> current OVS driver responsible for setting up the vswitch
> and then having a ToR driver (e.g. Big Switch, Arista,
> etc) responsible for setting up the fabric. Additionally,
> there is a separate L3 plugin (e.g. the reference one,
> Vyatta, etc) for providing routing.
>
> I suppose with an overlay it's easier to take the route
> that you don't want to be compatible with other networking
> stuff at the Neutron layer (e.g. integration with the 3rd
> parties is orchestrated somewhere else). In that case, the
> above scenario wouldn't make much sense to support, but
> it's worth keeping in mind.
>
> On Mon, Feb 23, 2015 at 10:28 AM, Salvatore Orlando
> <sorlando at nicira.com <mailto:sorlando at nicira.com>> wrote:
>
> I think there are a few factors which influence the
> ML2 driver vs "monolithic" plugin debate, and they
> mostly depend on OVN rather than Neutron.
> From a Neutron perspective both plugins and drivers
> (as long at they live in their own tree) will be
> supported in the foreseeable future. If a ML2 mech
> driver is not the best option for OVN that would be ok
> - I don't think the Neutron community advices
> development of a ML2 driver as the preferred way for
> integrating with new backends.
>
> The ML2 framework provides a long list of benefits
> that mechanism driver developer can leverage.
> Among those:
> - The ability of leveraging Type drivers which
> relieves driver developers from dealing with network
> segment allocation
> - Post-commit and (for most operations) pre-commit
> hooks for performing operation on the backend
> - The ability to leverage some of the features offered
> by Neutron's built-in control-plane such as L2-population
> - A flexible mechanism for enabling driver-specific
> API extensions
> - Promotes modular development and integration with
> higher-layer services, such as L3. For instance OVN
> could provide the L2 support for Neutron's built-in L3
> control plane
> - The (potential afaict) ability of interacting with
> other mechanism driver such as those operating on
> physical appliances on the data center
> - <add your benefit here>
>
> In my opinion OVN developers should look at ML2
> benefits, and check which ones apply to this specific
> platform. I'd say that if there are 1 or 2 checks in
> the above list, maybe it would be the case to look at
> developing a ML2 mechanism driver, and perhaps a L3
> service plugin.
> It is worth nothing that ML2, thanks to its type and
> mechanism driver provides also some control plane
> capabilities. If those capabilities are however on
> OVN's roadmap it might be instead worth looking at a
> "monolithic" plugin, which can also be easily
> implemented by inheriting from
> neutron.db.db_base_plugin_v2.NeutronDbPluginV2, and
> then adding all the python mixins for the extensions
> the plugin needs to support.
>
> Salvatore
>
>
> On 23 February 2015 at 18:32, Ben Pfaff
> <blp at nicira.com <mailto:blp at nicira.com>> wrote:
>
> [branching off a discussion on ovs-dev at this point:
> http://openvswitch.org/pipermail/dev/2015-February/051609.html]
>
> On Fri, Feb 20, 2015 at 6:56 PM, Kyle Mestery
> <mestery at mestery.com <mailto:mestery at mestery.com>>
> wrote:
> > One thing to keep in mind, this ties somewhat
> into my response to Russell
> > earlier on the decision around ML2 vs. core
> plugin. If we do ML2, there are
> > type drivers for VLAN, VXLAN, and GRE tunnels.
> There is no TypeDriver for
> > STT tunnels upstream now. It's just an item we
> need on the TODO list if we
> > go down the STT tunnel path.
>
> It was suggested to me off-list that this part of
> the discussion should be on
> openstack-dev, so here it is ;-)
>
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> --
> Kevin Benton
>
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