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Alternatively, we could just consider the ec2 mapping layer to be global data that must be replicated somehow across the system.  I don't think we can really ensure no collisions mapping from uuid -> ec2_id deterministically, and I don't see a clear path forward when we do get a collision.

Vish

On May 8, 2012, at 12:24 AM, Michael Still wrote:

> On 04/05/12 20:31, Eoghan Glynn wrote:
> 
> Sorry for the slow reply, I've been trapped in meetings.
> 
> [snip]
> 
>> So the way things currently stand, the EC2 image ID isn't really capable of
>> migration.
>> 
>> I was thinking however that we should change the EC2 image generation logic,
>> so that there is a reproducible glance UUID -> EC2 mapping (with a small
>> chance of collision). This change would allow the same EC2 ID to be generated
>> in multiple regions for a given glance UUID (modulo collisions).
>> 
>> Would that be helpful in your migration use-case?
> 
> I do think this is a good idea. Or even if the column wasn't
> auto-increment, but just picked a random number or something (because
> that would be marginally less likely to clash). Without somehow making
> these ec2 ids more global, replication between regions is going to
> suffer from ec2 api users having to somehow perform a lookup out of band.
> 
> Now, my use case is a bit special, because I can enforce that images are
> only ever uploaded to one master region, and then copied to all others.
> I think that's probably not true for other users though.
> 
> Mikal
> 
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