[openstack-dev] [neutron][TripleO] Clear all flows when ovs agent start? why and how avoid?

Germy Lure germy.lure at gmail.com
Wed Nov 5 09:46:25 UTC 2014

Hi Salvatore,
A startup flag is really a simpler approach. But in what situation we
should set this flag to remove all flows? upgrade? restart manually?
internal fault?

Indeed, only at the time that there are inconsistent(incorrect, unwanted,
stable and so on) flows between agent and the ovs related, we need refresh
flows. But the problem is how we know this? I think a startup flag is too
rough, unless we can tolerate the inconsistent situation.

Of course, I believe that turn off startup reset flows action can resolve
most problem. The flows are correct most time after all. But considering
NFV 5 9s, I still recommend flow synchronization approach.


On Wed, Nov 5, 2014 at 3:36 PM, Salvatore Orlando <sorlando at nicira.com>

> From what I gather from this thread and related bug report, the change
> introduced in the OVS agent is causing a data plane outage upon agent
> restart, which is not desirable in most cases.
> The rationale for the change that introduced this bug was, I believe,
> cleaning up stale flows on the OVS agent, which also makes some sense.
> Unless I'm missing something, I reckon the best way forward is actually
> quite straightforward; we might add a startup flag to reset all flows and
> not reset them by default.
> While I agree the "flow synchronisation" process proposed in the previous
> post is valuable too, I hope we might be able to fix this with a simpler
> approach.
> Salvatore
> On 5 November 2014 04:43, Germy Lure <germy.lure at gmail.com> wrote:
>> Hi,
>> Consider the triggering of restart agent, I think it's nothing but:
>> 1). only restart agent
>> 2). reboot the host that agent deployed on
>> When the agent started, the ovs may:
>> a.have all correct flows
>> b.have nothing at all
>> c.have partly correct flows, the others may need to be reprogrammed,
>> deleted or added
>> In any case, I think both user and developer would happy to see that the
>> system recovery ASAP after agent restarting. The best is agent only push
>> those incorrect flows, but keep the correct ones. This can ensure those
>> business with correct flows working during agent starting.
>> So, I suggest two solutions:
>> 1.Agent gets all flows from ovs and compare with its local flows after
>> restarting. And agent only corrects the different ones.
>> 2.Adapt ovs and agent. Agent just push all(not remove) flows every time
>> and ovs prepares two tables for flows switch(like RCU lock).
>> 1 is recommended because of the 3rd vendors.
>> BR,
>> Germy
>> On Fri, Oct 31, 2014 at 10:28 PM, Ben Nemec <openstack at nemebean.com>
>> wrote:
>>> On 10/29/2014 10:17 AM, Kyle Mestery wrote:
>>> > On Wed, Oct 29, 2014 at 7:25 AM, Hly <henry4hly at gmail.com> wrote:
>>> >>
>>> >>
>>> >> Sent from my iPad
>>> >>
>>> >> On 2014-10-29, at 下午8:01, Robert van Leeuwen <
>>> Robert.vanLeeuwen at spilgames.com> wrote:
>>> >>
>>> >>>>> I find our current design is remove all flows then add flow by
>>> entry, this
>>> >>>>> will cause every network node will break off all tunnels between
>>> other
>>> >>>>> network node and all compute node.
>>> >>>> Perhaps a way around this would be to add a flag on agent startup
>>> >>>> which would have it skip reprogramming flows. This could be used for
>>> >>>> the upgrade case.
>>> >>>
>>> >>> I hit the same issue last week and filed a bug here:
>>> >>> https://bugs.launchpad.net/neutron/+bug/1383674
>>> >>>
>>> >>> From an operators perspective this is VERY annoying since you also
>>> cannot push any config changes that requires/triggers a restart of the
>>> agent.
>>> >>> e.g. something simple like changing a log setting becomes a hassle.
>>> >>> I would prefer the default behaviour to be to not clear the flows or
>>> at the least an config option to disable it.
>>> >>>
>>> >>
>>> >> +1, we also suffered from this even when a very little patch is done
>>> >>
>>> > I'd really like to get some input from the tripleo folks, because they
>>> > were the ones who filed the original bug here and were hit by the
>>> > agent NOT reprogramming flows on agent restart. It does seem fairly
>>> > obvious that adding an option around this would be a good way forward,
>>> > however.
>>> Since nobody else has commented, I'll put in my two cents (though I
>>> might be overcharging you ;-).  I've also added the TripleO tag to the
>>> subject, although with Summit coming up I don't know if that will help.
>>> Anyway, if the bug you're referring to is the one I think, then our
>>> issue was just with the flows not existing.  I don't think we care
>>> whether they get reprogrammed on agent restart or not as long as they
>>> somehow come into existence at some point.
>>> It's possible I'm wrong about that, and probably the best person to talk
>>> to would be Robert Collins since I think he's the one who actually
>>> tracked down the problem in the first place.
>>> -Ben
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