On Wed, 2020-04-29 at 10:39 +0200, Ignazio Cassano wrote:
> Hello, some updated about this issue.
> I read someone has got same issue as reported here:
>
> https://bugs.launchpad.net/neutron/+bug/1866139
>
> If you read the discussion, someone tells that the garp must be sent by
> qemu during live miration.
> If this is true, this means on rocky/stein the qemu/libvirt are bugged.
it is not correct.
qemu/libvir thas alsway used RARP which predates GARP to serve as its mac learning frames
instead https://en.wikipedia.org/wiki/Reverse_Address_Resolution_Protocol
https://lists.gnu.org/archive/html/qemu-devel/2009-10/msg01457.html
however it looks like this was broken in 2016 in qemu 2.6.0
https://lists.gnu.org/archive/html/qemu-devel/2016-07/msg04645.html
but was fixed by https://github.com/qemu/qemu/commit/ca1ee3d6b546e841a1b9db413eb8fa09f13a061b
can you confirm you are not using the broken 2.6.0 release and are using 2.7 or newer or 2.4 and older.


> So I tried to use stein and rocky with the same version of libvirt/qemu
> packages I installed on queens (I updated compute and controllers node on
> queens for obtaining same libvirt/qemu version deployed on rocky and stein).
>
> On queens live migration on provider network continues to work fine.
> On rocky and stein not, so I think the issue is related to openstack
> components .
on queens we have only a singel prot binding and nova blindly assumes that the port binding details wont
change when it does a live migration and does not update the xml for the netwrok interfaces.

the port binding is updated after the migration is complete in post_livemigration
in rocky+ neutron optionally uses the multiple port bindings flow to prebind the port to the destiatnion
so it can update the xml if needed and if post copy live migration is enable it will asyconsly activate teh dest port
binding before post_livemigration shortenting the downtime.

if you are using the iptables firewall os-vif will have precreated the ovs port and intermediate linux bridge before the
migration started which will allow neutron to wire it up (put it on the correct vlan and install security groups) before
the vm completes the migraton.

if you are using the ovs firewall os-vif still precreates teh ovs port but libvirt deletes it and recreats it too.
as a result there is a race when using openvswitch firewall that can result in the RARP packets being lost.

>
> Best Regards
> Ignazio Cassano
>
>
>
>
> Il giorno lun 27 apr 2020 alle ore 19:50 Sean Mooney <smooney@redhat.com>
> ha scritto:
>
> > On Mon, 2020-04-27 at 18:19 +0200, Ignazio Cassano wrote:
> > > Hello, I have this problem with rocky or newer with iptables_hybrid
> > > firewall.
> > > So, can I solve using post copy live migration ???
> >
> > so this behavior has always been how nova worked but rocky the
> >
> > https://specs.openstack.org/openstack/nova-specs/specs/rocky/implemented/neutron-new-port-binding-api.html
> > spec intoduced teh ablity to shorten the outage by pre biding the port and
> > activating it when
> > the vm is resumed on the destiation host before we get to pos live migrate.
> >
> > this reduces the outage time although i cant be fully elimiated as some
> > level of packet loss is
> > always expected when you live migrate.
> >
> > so yes enabliy post copy live migration should help but be aware that if a
> > network partion happens
> > during a post copy live migration the vm will crash and need to be
> > restarted.
> > it is generally safe to use and will imporve the migration performace but
> > unlike pre copy migration if
> > the guess resumes on the dest and the mempry page has not been copied yet
> > then it must wait for it to be copied
> > and retrive it form the souce host. if the connection too the souce host
> > is intrupted then the vm cant
> > do that and the migration will fail and the instance will crash. if you
> > are using precopy migration
> > if there is a network partaion during the migration the migration will
> > fail but the instance will continue
> > to run on the source host.
> >
> > so while i would still recommend using it, i it just good to be aware of
> > that behavior change.
> >
> > > Thanks
> > > Ignazio
> > >
> > > Il Lun 27 Apr 2020, 17:57 Sean Mooney <smooney@redhat.com> ha scritto:
> > >
> > > > On Mon, 2020-04-27 at 17:06 +0200, Ignazio Cassano wrote:
> > > > > Hello, I have a problem on stein neutron. When a vm migrate from one
> >
> > node
> > > > > to another I cannot ping it for several minutes. If in the vm I put a
> > > > > script that ping the gateway continously, the live migration works
> >
> > fine
> > > >
> > > > and
> > > > > I can ping it. Why this happens ? I read something about gratuitous
> >
> > arp.
> > > >
> > > > qemu does not use gratuitous arp but instead uses an older protocal
> >
> > called
> > > > RARP
> > > > to do mac address learning.
> > > >
> > > > what release of openstack are you using. and are you using iptables
> > > > firewall of openvswitch firewall.
> > > >
> > > > if you are using openvswtich there is is nothing we can do until we
> > > > finally delegate vif pluging to os-vif.
> > > > currently libvirt handels interface plugging for kernel ovs when using
> >
> > the
> > > > openvswitch firewall driver
> > > > https://review.opendev.org/#/c/602432/ would adress that but it and
> >
> > the
> > > > neutron patch are
> > > > https://review.opendev.org/#/c/640258 rather out dated. while libvirt
> >
> > is
> > > > pluging the vif there will always be
> > > > a race condition where the RARP packets sent by qemu and then mac
> >
> > learning
> > > > packets will be lost.
> > > >
> > > > if you are using the iptables firewall and you have opnestack rock or
> > > > later then if you enable post copy live migration
> > > > it should reduce the downtime. in this conficution we do not have the
> >
> > race
> > > > betwen neutron and libvirt so the rarp
> > > > packets should not be lost.
> > > >
> > > >
> > > > > Please, help me ?
> > > > > Any workaround , please ?
> > > > >
> > > > > Best Regards
> > > > > Ignazio
> > > >
> > > >
> >
> >