[openstack-dev] [neutron][sfc] How could an L2 agent extension access agent methods ?

Henry Fourie louis.fourie at huawei.com
Tue Nov 10 23:35:58 UTC 2015


Ihar,
   Networking-sfc installs flows on br-int and br-tun for steering
traffic to the SFC port-pairs. On each bridge additional tables are used
for an egress forwarding pipeline (from the service VM port) and an
ingress pipeline (to the service VM port). Rpc operations between the
OVS driver and agents is used to initiate the flow installation.

We'd like to work with you on defining the L2 extensions.

 - Louis


- 
-----Original Message-----
From: Ihar Hrachyshka [mailto:ihrachys at redhat.com] 
Sent: Monday, November 09, 2015 4:44 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [neutron][sfc] How could an L2 agent extension access agent methods ?

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/agen
>>>>> t/l2/extensions/qos.py#n169
>>>>> [2]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plug
>>>>> ins/ml2/drivers/mech_sriov/agent/extension_drivers/qos_driver.py
>>>>> [3]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plug
>>>>> ins/ml2/drivers/openvswitch/agent/extension_drivers/qos_driver.py
>>>>> [4]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plug
>>>>> ins/ml2/drivers/openvswitch/agent/ovs_neutron_agent.py#n395
>>>>> [5]:  
>>>>> https://git.openstack.org/cgit/openstack/neutron/tree/neutron/plug
>>>>> ins/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 
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>>>>>
>>>>> Ihar
>
>
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