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[Ilya Kharin <akscram@xxxxxxxxx>]

There is yet approach on multi-host scheme with VlanManager for solve problem with default gateway in VM. Look at the mechanism:
1. run live_migration from node-1 to node-2
2. reconfigure dnsmasq and drop lease  on node-1
3. reconfigure dnsmasq on node-2

Realization by hands on test stand. At first run live migration of instance (ip=10.0.0.8 and mac=02:16:3e:6b:40:85 host=node-1):
$ nova-manage vm live_migration --ec2_id=i-00000008 --dest=node-2
then on node-1 reconfigure dnsmasq and drop lease (send fake DHCPRELEASE message to server):
$ killall -s HUP dnsmasq
$ dhcp_release br100 10.0.0.8 02:16:3e:6b:40:85
reconfigure dnsmasq on node-2:
$ killall -s HUP dnsmasq
On next DHCP request from VM dnsmasq from node-2 send replay with correct gw.

Reconfiguration command (kill -HUP) from python implemented in nova.network.linux_net.restart_dhcp() and dhcp_release in nova.network.linux_net.release_dhcp().

Step (2) can be implemented in nova.compute.manager.live_migration before made RPC call nova.compute.manager.post_live_migration_at_destination() and step (3) in this function which executed on destination node.

--
Regards,
Ilya Kharin.


On 07.02.2012, at 23:06, Vishvananda Ishaya wrote:

> Live migration will still work, it just means that your old host will still be dhcp, gateway. and floating ip host for the vm.  A fix for moving the floating ip should be simple. Moving the dhcp host is a little harder, due to having to update security group rules to allow dhcp traffic as well.  Moving the gateway is even harder, because you will have to leave the old gateway up until you are sure the dhcp lease has been renewed.
> 
> Patches for the first seems like a bug fix that someone could do for essex. The second is questionable but possible. The last is probably to complex for Essex, but could be addressed in Folsom if quantum doesn't have a better solution.
> 
> Vish
> 
> On Feb 7, 2012, at 9:01 AM, David Kranz wrote:
> 
>> There was a thread about this in December: http://www.mail-archive.com/openstack@xxxxxxxxxxxxxxxxxxx/msg06296.html
>> 
>> I think that thread is saying that if you follow the official documentation for configuring live migration, but use --multi_host, then
>> migration will not actually work. If that is right, is there (or will there be)  an officially documented way to to this, either for diablo or essex?
>> 
>> -David
>> 
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