[openstack-dev] [nova-compute][nova][libvirt] Extending Nova-Compute for image prefetching

Michael Still mikal at stillhq.com
Thu Oct 8 20:45:55 UTC 2015

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?


On Thu, Oct 8, 2015 at 10:50 PM, Alberto Geniola <albertogeniola at gmail.com>

> 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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