[openstack-dev] [heat] [glance] Heater Proposal

James Slagle james.slagle at gmail.com
Thu Dec 5 16:35:12 UTC 2013

On Thu, Dec 5, 2013 at 11:10 AM, Clint Byrum <clint at fewbar.com> wrote:
> Excerpts from Monty Taylor's message of 2013-12-04 17:54:45 -0800:
>> Why not just use glance?
> I've asked that question a few times, and I think I can collate the
> responses I've received below. I think enhancing glance to do these
> things is on the table:

I'm actually interested in the use cases laid out by Heater from both
a template perspective and image perspective.  For the templates, as
Robert mentioned, Tuskar needs a solution for this requirement, since
it's deploying using templates.  For the images, we have the concept
of a "golden" image in TripleO and are heavily focused on image based
deployments.  Therefore, it seems to make sense that TripleO also
needs a way to version/tag known good images.

Given that, I think it makes sense  to do this in a way so that it's
consumable for things other than just templates.  In fact, you can
almost s/template/image/g on the Heater wiki page, and it pretty well
lays out what I'd like to see for images as well.

> 1. Glance is for big blobs of data not tiny templates.
> 2. Versioning of a single resource is desired.
> 3. Tagging/classifying/listing/sorting
> 4. Glance is designed to expose the uploaded blobs to nova, not users
> My responses:
> 1: Irrelevant. Smaller things will fit in it just fine.
> 2: The swift API supports versions. We could also have git as a
> backend.

I would definitely like to see a git backend for versioning.  No
reason to reimplement a different solution for what already works
well.  I'm not sure we'd want to put a whole image into git though.
Perhaps just it's manifest (installed components, software versions,
etc) in json format would go into git, and that would be associated
back to the binary image via uuid.  That would even make it easy to
diff changes between versions, etc.

> This feels like something we can add as an optional feature
> without exploding Glance's scope and I imagine it would actually be a
> welcome feature for image authors as well. Think about Ubuntu maintaining
> official images. If they can keep the ID the same and just add a version
> (allowing users to lock down to a version if updated images cause issue)
> that seems like a really cool feature for images _and_ templates.
> 3: I'm sure glance image users would love to have those too.
> 4: Irrelevant. Heat will need to download templates just like nova, and
> making images publicly downloadable is also a thing in glance.
> It strikes me that this might be a silo problem instead of an
> actual design problem. Folk should not be worried about jumping into
> Glance and adding features. Unless of course the Glance folk have
> reservations? (adding glance tag to the subject)

I'm +1 for adding these types of features to glance, or at least
something common, instead of making it specific to Heat templates.

-- James Slagle

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