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Hi,

I've noticed that when an instance is created the scheduler hints (if passed) are thrown away.  This may or may not be a bug. Consider the following scenario. 

You have a scheduler hint where you want the scheduler to pick resources that are in close proximity to a particular ip address. 

ex:
scheduler_hints': { 'cidr': '/32',
                                'build_near_host_ip': affinity_ip}

<time passes>

Now you migrate the instance to a different host. There are no hints since they weren't saved and unless the person issuing the migration command remembers the desire for affinity, it becomes a matter of luck if the affinity will be broken. To me this makes the case that if scheduler_hints are initially passed they should be saved, such that if there is a later migration the filter should be applied against the desired destination and if that destination doesn't pass the filter an error should be raised. 

I have an initial implementation that can be found at : git://gitorious.org/nova/nova.git  
                                                                               branch: 	respect_scheduler_hints_during_migration

Thoughts?

Regards,
Tom