I guess this blueprint[1] attempted to implement the flow synchronization issue 
during the agent restart.
But I see no progress/updates. It would be helpful to know about the progress 
there.

[1] https://blueprints.launchpad.net/neutron/+spec/neutron-agent-soft-restart

On a different note, I agree with Salvatore on getting started with the 
simplistic approach and improve it further.

Regards,
Sudhakar.

From: Salvatore Orlando [mailto:sorla...@nicira.com]
Sent: Wednesday, November 05, 2014 4:39 PM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [neutron][TripleO] Clear all flows when ovs agent 
start? why and how avoid?

I have no opposition to that, and I will be happy to assist reviewing the code 
that will enable flow synchronisation  (or to say it in an easier way, punctual 
removal of flows unknown to the l2 agent).

In the meanwhile, I hope you won't mind if we go ahead and start making flow 
reset optional - so that we stop causing downtime upon agent restart.

Salvatore

On 5 November 2014 11:57, Erik Moe 
<erik....@ericsson.com<mailto:erik....@ericsson.com>> wrote:

Hi,

I also agree, IMHO we need flow synchronization method so we can avoid network 
downtime and stray flows.

Regards,
Erik


From: Germy Lure [mailto:germy.l...@gmail.com<mailto:germy.l...@gmail.com>]
Sent: den 5 november 2014 10:46
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [neutron][TripleO] Clear all flows when ovs agent 
start? why and how avoid?

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.

BR,
Germy

On Wed, Nov 5, 2014 at 3:36 PM, Salvatore Orlando 
<sorla...@nicira.com<mailto:sorla...@nicira.com>> wrote:
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.l...@gmail.com<mailto:germy.l...@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 
<openst...@nemebean.com<mailto:openst...@nemebean.com>> wrote:
On 10/29/2014 10:17 AM, Kyle Mestery wrote:
> On Wed, Oct 29, 2014 at 7:25 AM, Hly 
> <henry4...@gmail.com<mailto:henry4...@gmail.com>> wrote:
>>
>>
>> Sent from my iPad
>>
>> On 2014-10-29, at 下午8:01, Robert van Leeuwen 
>> <robert.vanleeu...@spilgames.com<mailto:robert.vanleeu...@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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