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On 27/09/2016, 18:12, "Daniel P. Berrange" <berrange at redhat.com> wrote:

>On Tue, Sep 27, 2016 at 10:40:34AM -0600, Chris Friesen wrote:
>> On 09/27/2016 10:17 AM, Matthew Booth wrote:
>> 
>> > I think we should be able to create a domain, but once created we should never
>> > redefine a domain. We can do adding and removing devices dynamically using
>> > libvirt's apis, secure in the knowledge that libvirt will persist this for us.
>> > When we upgrade the host, libvirt can ensure we don't break guests which are on
>> > it. Evacuate should be pretty much the only reason to start again.
>> 
>> Sounds interesting.  How would you handle live migration?
>> 
>> Currently we regenerate the XML file on the destination from the nova DB.  I
>> guess in your proposal we'd need some way of copying the XML file from the
>> source to the dest, and then modifying the appropriate segments to adjust
>> things like CPU/NUMA pinning?
>
>Use the flag VIR_MIGRATE_PERSIST_XML and libvirt will write out the
>new persistent XML on the target host automatically.

We have a problem migrating rescued instances that has a fix in progress based
on regenerating the xml on unrescue, see:

 https://blueprints.launchpad.net/nova/+spec/live-migrate-rescued-instances 

That might be another case for generating the xml.

Paul


>
>Regards,
>Daniel
>-- 
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>
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