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Hi Jake,

Thanks for raising this topic. I'm really interested in it. I reviewed 
most of the locations patches of Glance, so drop my 2 cents about this. 
So firstly, I think it's a valid user case. As for the implementation, I 
think a spec-lite is enough, given it's just a driver for current 
location strategy. I haven't seen your code, so I'm not sure if your 
implementation is ok for upstreaming. But I would assume your code is a 
driver under 
https://github.com/openstack/glance/tree/master/glance/common/location_strategy 
and personally, I think the metadata of location is right way since the 
location URL can't provide clear and enough information for the ranking. 
We can discuss more on #openstack-glance channel. Cheers.

On 14/01/16 13:07, Jake Yip wrote:
> Hi all,
>
> I've recently ran across a constraint in glance-api while working with 
> image locations. In essence, there is no way to customize ordering of 
> image-locations other than the default location strategies, namely 
> location_order and store_type [0]. It seems like a more generic method 
> of ordering image locations is needed, IMHO.
>
> Some background - We are in a multi-cell environment and each cell has 
> it's own glance-api server. All images are stored in a global swift 
> cluster. We would like glance to be able to fetch images from a local 
> store, so that we can do COW for backends like RBD.
>
> Unfortunately, none of the current location strategies works for us, 
> as we might have multiple cells sharing the same backend. I've opened 
> a bug / wishlist describing this issue [1]. I have also implemented 
> code that allows us to achieve that based on image location metadata.
>
> I am wondering anyone else have solved this before? I would like to 
> hear your opinions on how we can achieve this, and whether ranking it 
> by metadata is the way to go.
>
> The current wishlist is now tracked as a spec-lite. Is this ok?
>
> Regards,
> Jake
>
> [0] 
> http://docs.openstack.org/liberty/config-reference/content/section_glance-api.conf.html
> [1] https://bugs.launchpad.net/glance/+bug/1528453
>
>
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-- 
Cheers & Best regards,
Fei Long Wang (王飞龙)
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