Re: [Xen-users] Live Migration where IP Changes are necessary

[Ernst Bachmann <e.bachmann@xxxxxxxx>]

On Sunday 30 October 2005 00:05, Jonathon Jones wrote:
> Hey guys,
>
> Thanks in advance for your help with this.  I have a domU that I need to
> migrate to another Xen server on a different network.  Basically I am
> moving to a new provider in the same datacenter.  the problem I am
> having which I am not sure how to overcome, is that I need to migrate my
> domU, but my current IP's are no good in the new environment.  Is there
> any way i can make live migration work with IP Changes?

Well, once you change your IP, currently open TCP connections are lost, so 
you'll loose the main advantage of a live migration anyways. 
Just change the ip in domU, save the state, copy it over and start it on the 
new host again.

Next problem would be filesystems: they'll have to be available at both 
providers in that datacenter, meaning all FS accesses (including SWAP) will 
have to run over the internet, which will be VERY slow at least, esp. when 
running over some VPN (you wouldn't want to run NFS over internet...)

Well, maybe your two providers allow you some sort of direct link between your 
two machines, so you might be able to overcome that problem.

Last problem would be the actual changing of your IP adress: xen doens't know 
nor care what protocols you run over your network devices, so it doesn't 
offer anything (besides some network-setup scripts) to mangle with the 
internal network stacks inside a domU. So, the IP change has to be initiated 
from inside domU, which in turn means the domU has to know its about to be 
migrated, which is somewhat against the "spirit" behind the xen live-migrate 
mechanism.


Only way I think you can make it work at least a bit would be:

run the domU with a private IP (192.168.1.1 for example)
have the dom0 on machine1 dnat the required ports to that ip, snat traffic 
coming from the domU.
add the same dnat rules to machine2.

Now you can migrate your domU between them, and the network setup stays the 
same from the domU's point of view.


/Ernst

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