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Thanks Thomas, much appreciated.

I need to admit that we haven’t heard from SFC folks just yet. I will try  
to raise awareness that we wait for their feedback today on team meeting.  
Adding [sfc] tag to the topic to get more attention.

Ihar

Thomas Morin <thomas.morin at orange.com> wrote:

> Hi Ihar,
>
> Ihar Hrachyshka :
>> Reviving the thread.
>> [...] (I appreciate if someone checks me on the following though):
>
> This is an excellent recap.
>
>>  I set up a new etherpad to collect feedback from subprojects [2].
>
> I've filled in details for networking-bgpvpn.
> Please tell me if you need more information.
>
>> Once we collect use cases there and agree on agent API for extensions  
>> (even if per agent type), we will implement it and define as stable API,  
>> then pass objects that implement the API into extensions thru extension  
>> manager. If extensions support multiple agent types, they can still  
>> distinguish between which API to use based on agent type string passed  
>> into extension manager.
>>
>> I really hope we start to collect use cases early so that we have time  
>> to polish agent API and make it part of l2 extensions earlier in Mitaka  
>> cycle.
>
> We'll be happy to validate the applicability of this approach as soon as  
> something is ready.
>
> Thanks for taking up this work!
>
> -Thomas
>
>
>
>> Ihar Hrachyshka <ihrachys at redhat.com> wrote:
>>
>>>> On 30 Sep 2015, at 12:53, Miguel Angel Ajo <mangelajo at redhat.com> wrote:
>>>>
>>>>
>>>>
>>>> Ihar Hrachyshka wrote:
>>>>>> On 30 Sep 2015, at 12:08, thomas.morin at orange.com wrote:
>>>>>>
>>>>>> Hi Ihar,
>>>>>>
>>>>>> Ihar Hrachyshka :
>>>>>>>> Miguel Angel Ajo :
>>>>>>>>> Do you have a rough idea of what operations you may need to do?
>>>>>>>> Right now, what bagpipe driver for networking-bgpvpn needs to  
>>>>>>>> interact with is:
>>>>>>>> - int_br OVSBridge (read-only)
>>>>>>>> - tun_br OVSBridge (add patch port, add flows)
>>>>>>>> - patch_int_ofport port number (read-only)
>>>>>>>> - local_vlan_map dict (read-only)
>>>>>>>> - setup_entry_for_arp_reply method (called to add static ARP  
>>>>>>>> entries)
>>>>>>> Sounds very tightly coupled to OVS agent.
>>>>>>>>> Please bear in mind, the extension interface will be available  
>>>>>>>>> from different agent types
>>>>>>>>> (OVS, SR-IOV, [eventually LB]), so this interface you're talking  
>>>>>>>>> about could also serve as
>>>>>>>>> a translation driver for the agents (where the translation is  
>>>>>>>>> possible), I totally understand
>>>>>>>>> that most extensions are specific agent bound, and we must be  
>>>>>>>>> able to identify
>>>>>>>>> the agent we're serving back exactly.
>>>>>>>> Yes, I do have this in mind, but what we've identified for now  
>>>>>>>> seems to be OVS specific.
>>>>>>> Indeed it does. Maybe you can try to define the needed pieces in  
>>>>>>> high level actions, not internal objects you need to access to.  
>>>>>>> Like ‘- connect endpoint X to Y’, ‘determine segmentation id for a  
>>>>>>> network’ etc.
>>>>>> I've been thinking about this, but would tend to reach the  
>>>>>> conclusion that the things we need to interact with are pretty hard  
>>>>>> to abstract out into something that would be generic across  
>>>>>> different agents.  Everything we need to do in our case relates to  
>>>>>> how the agents use bridges and represent networks internally:  
>>>>>> linuxbridge has one bridge per Network, while OVS has a limited  
>>>>>> number of bridges playing different roles for all networks with  
>>>>>> internal segmentation.
>>>>>>
>>>>>> To look at the two things you  mention:
>>>>>> - "connect endpoint X to Y" : what we need to do is redirect the  
>>>>>> traffic destinated to the gateway of a Neutron network, to the thing  
>>>>>> that will do the MPLS forwarding for the right BGP VPN context  
>>>>>> (called VRF), in our case br-mpls (that could be done with an OVS  
>>>>>> table too) ; that action might be abstracted out to hide the details  
>>>>>> specific to OVS, but I'm not sure on how to  name the destination in  
>>>>>> a way that would be agnostic to these details, and this is not  
>>>>>> really relevant to do until we have a relevant context in which the  
>>>>>> linuxbridge would pass packets to something doing MPLS forwarding  
>>>>>> (OVS is currently the only option we support for MPLS forwarding,  
>>>>>> and it does not really make sense to mix linuxbridge for Neutron  
>>>>>> L2/L3 and OVS for MPLS)
>>>>>> - "determine segmentation id for a network": this is something  
>>>>>> really OVS-agent-specific, the linuxbridge agent uses multiple linux  
>>>>>> bridges, and does not rely on internal segmentation
>>>>>>
>>>>>> Completely abstracting out packet forwarding pipelines in OVS and  
>>>>>> linuxbridge agents would possibly allow defining an interface that  
>>>>>> agent extension could use without to know about anything specific to  
>>>>>> OVS or the linuxbridge, but I believe this is a very significant  
>>>>>> taks to tackle.
>>>>>
>>>>> If you look for a clean way to integrate with reference agents, then  
>>>>> it’s something that we should try to achieve. I agree it’s not an  
>>>>> easy thing.
>>>>>
>>>>> Just an idea: can we have a resource for traffic forwarding, similar  
>>>>> to security groups? I know folks are not ok with extending security  
>>>>> groups API due to compatibility reasons, so maybe fwaas is the place  
>>>>> to experiment with it.
>>>>>
>>>>>> Hopefully it will be acceptable to create an interface, even it  
>>>>>> exposes a set of methods specific to the linuxbridge agent and a set  
>>>>>> of methods specific to the OVS agent.  That would mean that the  
>>>>>> agent extension that can work in both contexts (not our case yet)  
>>>>>> would check the agent type before using the first set or the second  
>>>>>> set.
>>>>>
>>>>> The assumption of the whole idea of l2 agent extensions is that they  
>>>>> are agent agnostic. In case of QoS, we implemented a common QoS  
>>>>> extension that can be plugged in any agent [1], and a set of backend  
>>>>> drivers (atm it’s just sr-iov [2] and ovs [3]) that are selected  
>>>>> based on the driver type argument passed into the extension manager  
>>>>> [4][5]. Your extension could use similar approach to select the  
>>>>> backend.
>>>>>
>>>>> [1]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/agent/l2/extensions/qos.py#n169
>>>>> [2]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/drivers/mech_sriov/agent/extension_drivers/qos_driver.py
>>>>> [3]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/drivers/openvswitch/agent/extension_drivers/qos_driver.py
>>>>> [4]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py#n395
>>>>> [5]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plugins/ml2/drivers/mech_sriov/agent/sriov_nic_agent.py#n155
>>>>
>>>> I disagree on the agent-agnostic thing. QoS extension for SR-IOV is  
>>>> totally not agnostic for OVS or LB, in the QoS case, it's just
>>>> accidental that OVS & LB share common bridges now due to the OVS  
>>>> Hybrid implementation that leverages linux bridge
>>>> and iptables.
>>>
>>> Wait. The QoS extension has nothing agent backend specific. All it does  
>>> is it receives rpc updates for tracked resources and pass them into qos  
>>> drivers. Those latter are the bits that implement backend specific  
>>> operations. So I am not sure why you say the extension itself is agent  
>>> specific: any other amqp based agent in the wild can adopt the  
>>> extension as-is, only providing a new backend to load.
>>>
>>>> I agree on having a well defined interface, on which API is available  
>>>> to talking back to each agent, and it has to be common, where
>>>> it's possible to be common.
>>>>
>>>> It doesn't have to be easy, but it's the way if we want a world where  
>>>> those commonalities and reusability of extensions can
>>>> exist and not be just accidental, but it's not realistic in my opinion  
>>>> to AIM for it on every shot. I believe we should try where we can
>>>> but we should be open to agent specific extensions. The idea of the  
>>>> extensions is that you can extend specific agents without
>>>> being forced to have the main loop hijacked, or eventually having off  
>>>> tree code plugged into our agents.
>>>
>>> Partially, yes. The culprit here is how much the extension API should  
>>> know about an agent. We can probably make the extension API completely  
>>> extendable by allowing agents to pass any random kwargs into the  
>>> extension manager that will forward them into extensions. Note that it  
>>> breaks current API for extensions and technically breaks it (not that I  
>>> know of any external extensions that could be affected so far).
>>>
>>>> There we should add support to identify the type of agent the  
>>>> extension works with (compatibility, versioning, etc..)
>>>
>>> We already pass the type into extension manager, and that’s how we plug  
>>> in the proper backend driver in QoS.
>>>
>>>>>> Does this approach make sense ?
>>>>>>
>>>>>> -Thomas
>>>>>>
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>>>>>
>>>>> Note that you should really avoid putting that ^^ kind of signature  
>>>>> into your emails intended for public mailing lists. If it’s  
>>>>> confidential, why do you send it to everyone? And sorry, folks will  
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>>>>> whatnot.
>>>>>
>>>>> Ihar
>
>
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