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Hi John,

First of all thank you for the tip about tags.

In order to understand what extra API are needed to implement this
mechanism, I think we need to focus on what should be done by this
component.

In my opinion, what we need on NOVA-COMPUTE side would be:
1) List all images prefetched on each nova-compute node
2) Trigger an image prefetch on a particular node
3) Remove an image from the cache

The rest of mechanism, in my opinion, is an Horizon plugin that interacts
with Glance and calls appropriate APIs above.

In order to avoid duplication on the compute nodes, I think that images
might be cached into /var/lib/nova/instances/_base/ , so they are
immediately ready to be used by nova-compute.
Given that, if the user inhibits the image deletion after 1 day of unusage
from the conf file, this mechanism may be very helpful.

In other words by implementing API listed above in nova, alongside
developing a simple horizon plugin, we should be able to provide this
interesting feature.

Do you see any problem with this approach?




On Thu, Aug 20, 2015 at 12:47 PM, John Garbutt <john at johngarbutt.com> wrote:

> On 19 August 2015 at 19:30, Alberto Geniola <albertogeniola at gmail.com>
> wrote:
> >
> > Hi everyone,
> >
> >
> > This is my first email to the OS developer forum, so forgive me if I
> misplaced the subject tags J.
>
> Welcome!
>
> For future posts, I hope this helps make it easier:
> https://wiki.openstack.org/wiki/MailingListEtiquette
>
>
> > Straight to the point: for a project we’re involved in, we think that a
> pre-fetcher mechanism would be great for a variety of use cases. There was
> an attempt with this blueprint:
> >
> >
> https://blueprints.launchpad.net/nova/+spec/nova-image-cache-management-2
> >
> > and a more recent one:
> >
> > https://blueprints.launchpad.net/python-novaclient/+spec/prefetch-image
> >
> > although both seems to be dead now.
> >
> > So I really want to get a feedback from the developer’s community
> whether (1) such a feature makes sense in general, and (2) it may be worth
> the integration of such a component in the OpenStack code. In fact,
> although we can solve our problem by developing an in-house component, it
> would be better to have it integrated in OpenStack, including Nova and
> Horizon, so I need the feedback from the OS Guru guys J.
> >
> >
> > What do you think?
>
> I think it does make some sense.
>
> The disagreement in the past is about agreeing what should live inside
> Nova, and what should live outside Nova.
>
> For me, I am OK having an API to trigger an image prefetch on a
> particular host (although in many cases doing a build on that host has
> the same affect).
>
> I think the rest of that mechanism should probably live outside of
> Nova and Glance. So the question is what extra API are required to
> create such a tool.
>
> Thanks,
> johnthetubaguy
>
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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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