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Hi Michael,

and thank you for your answer.

Indeed, what I want to do is to add methods to the ImageCache.py module
(listing, adding, deleting). So far, this module only takes care of image
deletion: this represents the "cache" of images. Now, I want to populate
the cache with some images on the hypervisor (as you mention) without
having any instance running it, yet. The method I want like to add should
call the appropriate method from the hypervisor driver (let's say libvirt)
to trigger the image download/creation without starting it (I guess
something like calling _create_image() should do the trick).

Your question is actually good: how will an user be  able to trigger this
image caching mechanism?
My idea is to extend the HTTP Nova Compute API. I would lilke to add a
resource, let's say "CachedImages", to the API tree. In this way,
interacting via CRUD operation we should be able to CALL/CAST rpc api and
interact with the imagecache module.

Is it clearer now? Do you see any problem in this approach?

Regards,

Alberto.




On Thu, Oct 8, 2015 at 11:45 PM, Michael Still <mikal at stillhq.com> wrote:

> I think I'd rephrase your definition of pre-fetched to be honest --
> something more like "images on this hypervisor node without a currently
> running instance". So, your operations would become:
>
>  - trigger an image prefetching
>  - list unused base images (and perhaps when they were last used)
>  - delete an unused image
>
> All of that would need to tie into the image cache management code so that
> its not stomping on your images. In fact, you're probably best of adding
> all of this as tweaks to the image cache manager anyways.
>
> One question though -- who is calling these APIs? Are you adding a central
> service to orchestrate these calls?
>
> Michael
>
>
>
> On Thu, Oct 8, 2015 at 10:50 PM, Alberto Geniola <albertogeniola at gmail.com
> > wrote:
>
>> Hi all,
>>
>> I'm considering to extend the Nova-Compute API in order to provide
>> image-prefetching capabilities to OS.
>>
>> In order to allow image prefetching, I ended up with the need to add
>> three different APIs on the nova-compute nodes:
>>
>>   1. Trigger an image prefetching
>>
>>   2. List prefetched images
>>
>>   3. Delete a prefetched image
>>
>>
>>
>> About the point 1 I saw I can re-use the libvirt driver function
>> _create_image() to trigger the image prefetching. However, this approach
>> will not store any information about the stored image locally. This leads
>> to an issue: how do I retrieve a list of already fetched images? A quick
>> and simple possibility would be having a local file, storing information
>> about the fetched images. Would it be acceptable? Is there any best
>> practice in OS community?
>>
>>
>>
>> Any ideas?
>>
>>
>> Ty,
>>
>> Al.
>>
>> --
>> Dott. Alberto Geniola
>>
>>   albertogeniola at gmail.com
>>   +39-346-6271105
>>   https://www.linkedin.com/in/albertogeniola
>>
>> Web: http://www.hw4u.it
>>
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>
>
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> Rackspace Australia
>
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-- 
Dott. Alberto Geniola

  albertogeniola at gmail.com
  +39-346-6271105
  https://www.linkedin.com/in/albertogeniola

Web: http://www.hw4u.it
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