Re: [Xen-users] Re: Live VM migration

[George Shuklin <george.shuklin@xxxxxxxxx>]

As far as I know, open vswitch not 'smart', it simply allow to control flow of frames (not packets!). I don't know if xapi somehow transmit new/old packets to old/new VM location, but anyway, this is not OVS works. You can see what happens to OVS in /etc/xensource/scripts/vif file (it's shell script to process plug/unplug).

The magic is the grace arp, guest sending from newer location to reconfigure all switches on net to send new frames to new location. Some kernels (f.e. current centos 6) are broken and have difficulties with migration. Others (f.e. 3.0 and most -xen kernels) works fine with this.

The migration process (for PV) is very cooperative process, I think you can easily detects migration  process and reacts to it (by issuing dhclient command f.e.). I don't know details, but I think they can be easily digged out from xapi source. My assumption is the xenstore usage, you can create application for domU which will subscribe for changes for this key (key shall be digged out from xapi sources) and reacts to it.

On 23.08.2011 19:07, Payal Shah wrote:

Hi,

I guess I didn't rephrase the question properly. I'm aware that we could do live VM migration with different susbnets. I wanted to know that with the help of Open vSwitch, can we migrate to VM to a new subnet and the Open vSwitch is smart enough to route the packets to the new subnet. Will the Open vSwitch be aware that the VM is in a new subnet??? Also is there any way that the VM could get an ip from the new subnet if there is a dhcp configured, and can Open vSwitch route packets to the new VM???

I hope this makes sense.. Thank you for the previous responses

On Tue, Aug 23, 2011 at 5:11 AM, George Shuklin-4 [via Xen] <ml-node+4726239-1420815721-238104@xxxxxxxxxxxxx> wrote:

I do hear about guys who change route tables on router (one /32 route
per VM) according to VM migration. I think this can be used, but it
require very tight integration between router reconfiguration and vm
migration.

Technically OVS is just switch, not a router, so you can migrate VM
between different ip networks.

XCP do require to have same 'network' object on source and destination
hosts but no one says they need to have same gateway.


В Пн., 22/08/2011 в 10:50 -0500, Payal Shah пишет:

> Hello ,
> Thank you for the reply. I got the results I was expecting.
>
>
> I had one more question regarding open vSwitch and live VM migration.
> Live VM migration requires that both the hosts should be in the same
> subnet. If the hosts are in different subnets then how can we do live
> VM migration? Can open vSwitch be used in this scenario?? Or is there
> any other virtual switch that can route the packets as per the new
> subnet?
>
>
> Thank you in advance
>
>
> On Wed, Aug 3, 2011 at 8:39 PM, George Shuklin

> <[hidden email]> wrote:
>         On XCP (1.1b, may be in XCP 1.0) there is a note in
>         xensource.log about %% of migration.
>        
>         And you can do xentrace in dom0 to see all hypercalls (but you
>         must understand what they means to get needed information).
>        
>         On 04.08.2011 00:42, Payal wrote:
>        
>        
>                 I have two hosts as Xen Server named host A and host B
>                 in the same network. A
>                 VM is created on Host A. Host A and B have a shared
>                 storage using NFS. While
>                 doing migration from host A to host B, how can I see
>                 the memory pages being
>                 migrated.
>                 If I run a small continuous program on the VM residing
>                 on host A, will the
>                 migration complete first or the sript running will
>                 complete first? How can I
>                 see that data is going in clear text? Is there a tool
>                 to see the packets
>                 going through? I tried using wireshark and spanning
>                 the ports, but I
>                 couldn't infer much. ANy help on this appreciated.
>                 Thank you,
>                
>                 --
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> --
> Payal Shah
> Dream as if you'll live forever, live as if you'll die today.
>
>
>

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