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+1 to this. Evan, can you report a bug (if one hasn't been reported yet) and propose the fix? Or else I can find someone else to propose it.

Vish

On Aug 23, 2012, at 1:38 PM, Evan Callicoat <diopter at gmail.com> wrote:

> Hello all!
> 
> I'm the original author of the hairpin patch, and things have changed a little bit in Essex and Folsom from the original Diablo target. I believe I can shed some light on what should be done here to solve the issue in either case.
> 
> ---
> For Essex (stable/essex), in nova/virt/libvirt/connection.py:
> ---
> 
> Currently _enable_hairpin() is only being called from spawn(). However, spawn() is not the only place that vifs (veth#) get added to a bridge (which is when we need to enable hairpin_mode on them). The more relevant function is _create_new_domain(), which is called from spawn() and other places. Without changing the information that gets passed to _create_new_domain() (which is just 'xml' from to_xml()), we can easily rewrite the first 2 lines in _enable_hairpin(), as follows:
> 
> def _enable_hairpin(self, xml):
>     interfaces = self.get_interfaces(xml['name'])
> 
> Then, we can move the self._enable_hairpin(instance) call from spawn() up into _create_new_domain(), and pass it xml as follows:
> 
> [...]
> self._enable_hairpin(xml)
> return domain
> 
> This will run the hairpin code every time a domain gets created, which is also when the domain's vif(s) gets inserted into the bridge with the default of hairpin_mode=0.
> 
> ---
> For Folsom (trunk), in nova/virt/libvirt/driver.py:
> ---
> 
> There've been a lot more changes made here, but the same strategy as above should work. Here, _create_new_domain() has been split into _create_domain() and _create_domain_and_network(), and _enable_hairpin() was moved from spawn() to _create_domain_and_network(), which seems like it'd be the right thing to do, but doesn't quite cover all of the cases of vif reinsertion, since _create_domain() is the only function which actually creates the domain (_create_domain_and_network() just calls it after doing some pre-work). The solution here is likewise fairly simple; make the same 2 changes to _enable_hairpin():
> 
> def _enable_hairpin(self, xml):
>     interfaces = self.get_interfaces(xml['name'])
> 
> And move it from _create_domain_and_network() to _create_domain(), like before:
> 
> [...]
> self._enable_hairpin(xml)
> return domain
> 
> I haven't yet tested this on my Essex clusters and I don't have a Folsom cluster handy at present, but the change is simple and makes sense. Looking at to_xml() and _prepare_xml_info(), it appears that the 'xml' variable _create_[new_]domain() gets is just a python dictionary, and xml['name'] = instance['name'], exactly what _enable_hairpin() was using the 'instance' variable for previously.
> 
> Let me know if this works, or doesn't work, or doesn't make sense, or if you need an address to send gifts, etc. Hope it's solved!
> 
> -Evan
> 
> On Thu, Aug 23, 2012 at 11:20 AM, Sam Su <susltd.su at gmail.com> wrote:
> Hi Oleg,
> 
> Thank you for your investigation. Good lucky!
> 
> Can you let me know if find how to fix the bug?
> 
> Thanks,
> Sam
> 
> On Wed, Aug 22, 2012 at 12:50 PM, Oleg Gelbukh <ogelbukh at mirantis.com> wrote:
> Hello,
> 
> Is it possible that, during snapshotting, libvirt just tears down virtual interface at some point, and then re-creates it, with hairpin_mode disabled again?
> This bugfix [https://bugs.launchpad.net/nova/+bug/933640] implies that fix works on spawn of instance. This means that upon resume after snapshot, hairpin is not restored. May be if we insert the _enable_hairpin() call in snapshot procedure, it helps.
> We're currently investigating this issue in one of our environments, hope to come up with answer by tomorrow.
> 
> --
> Best regards,
> Oleg
> 
> On Wed, Aug 22, 2012 at 11:29 PM, Sam Su <susltd.su at gmail.com> wrote:
> My friend has found a way to enable ping itself, when this problem happened. But not found why this happen.
> sudo echo "1" > /sys/class/net/br1000/brif/<virtual-interface-name>/hairpin_mode
> 
> I file a ticket to report this problem:
> https://bugs.launchpad.net/nova/+bug/1040255
> 
> hopefully someone can find why this happen and solve it.
> 
> Thanks,
> Sam
> 
> 
> On Fri, Jul 20, 2012 at 3:50 PM, Gabriel Hurley <Gabriel.Hurley at nebula.com> wrote:
> I ran into some similar issues with the _enable_hairpin() call. The call is allowed to fail silently and (in my case) was failing. I couldn’t for the life of me figure out why, though, and since I’m really not a networking person I didn’t trace it along too far.
> 
>  
> 
> Just thought I’d share my similar pain.
> 
>  
> 
> -          Gabriel
> 
>  
> 
> From: openstack-bounces+gabriel.hurley=nebula.com at lists.launchpad.net [mailto:openstack-bounces+gabriel.hurley=nebula.com at lists.launchpad.net] On Behalf Of Sam Su
> Sent: Thursday, July 19, 2012 11:50 AM
> To: Brian Haley
> Cc: openstack
> Subject: Re: [Openstack] VM can't ping self floating IP after a snapshot is taken
> 
>  
> 
> Thank you for your support.
> 
>  
> 
> I checked the file  nova/virt/libvirt/connection.py, the sentence  self._enable_hairpin(instance) is already added to the function  _hard_reboot().
> 
> It looks like there are some difference between taking snapshot and reboot instance. I tried to figure out how to fix this bug but failed. 
> 
>  
> 
> It will be much appreciated if anyone can give some hints.
> 
>  
> 
> Thanks,
> 
> Sam
> 
>  
> 
> On Thu, Jul 19, 2012 at 8:37 AM, Brian Haley <brian.haley at hp.com> wrote:
> 
> On 07/17/2012 05:56 PM, Sam Su wrote:
> > Hi,
> >
> > Just This always happens in Essex release. After I take a snapshot of my VM ( I
> > tried Ubuntu 12.04 or CentOS 5.8), VM can't ping its self floating IP; before I
> > take a snapshot though, VM can ping its self floating IP.
> >
> > This looks closely related to https://bugs.launchpad.net/nova/+bug/933640, but
> > still a little different. In 933640, it sounds like VM can't ping its self
> > floating IP regardless whether we take a snapshot or not.
> >
> > Any suggestion to make an easy fix? And what is the root cause of the problem?
> 
> It might be because there's a missing _enable_hairpin() call in the reboot()
> function.  Try something like this...
> 
> nova/virt/libvirt/connection.py, _hard_reboot():
> 
>              self._create_new_domain(xml)
> +            self._enable_hairpin(instance)
>              self.firewall_driver.apply_instance_filter(instance, network_info)
> 
> At least that's what I remember doing myself recently when testing after a
> reboot, don't know about snapshot.
> 
> Folsom has changed enough that something different would need to be done there.
> 
> -Brian
> 
>  
> 
> 
> 
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