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

Flavio Percoco flavio at redhat.com
Fri Dec 6 08:35:22 UTC 2013

On 05/12/13 15:36 -0800, Mark Washenberger wrote:
>On Thu, Dec 5, 2013 at 3:11 PM, Randall Burt <randall.burt at rackspace.com>
>    On Dec 5, 2013, at 4:45 PM, Steve Baker <sbaker at redhat.com>
>     wrote:
>        On 12/06/2013 10:46 AM, Mark Washenberger wrote:
>            On Thu, Dec 5, 2013 at 1:05 PM, Vishvananda Ishaya <
>            vishvananda at gmail.com> wrote:


>                This is not completely correct. Glance already supports
>                something akin to templates. You can create an "image" with
>                metadata properties that specifies a complex block device
>                mapping which would allow for multiple volumes and images to
>                connected to the vm at boot time. This is functionally a
>                template for a single vm.
>                Glance is pretty useless if is just an "image storage" service,
>                we already have other places that can store bits (swift,
>                cinder). It is much more valuable as a searchable repository of
>                bootable templates. I don't see any reason why this idea
>                couldn't be extended to include more complex templates that
>                could include more than one vm.
>            FWIW I agree with all of this. I think Glance's real role in
>            OpenStack is as a helper and optionally as a gatekeeper for the
>            category of "stuff Nova can boot". So any parameter that affects
>            what Nova is going to boot should in my view be something Glance
>            can be aware of. This list of parameters *could* grow to include
>            multiple device images, attached volumes, and other things that
>            currently live in the realm of flavors such as extra hardware
>            requirements and networking aspects.
>            Just so things don't go too crazy, I'll add that since Nova is
>            generally focused on provisioning individual VMs, anything above
>            the level of an individual VM should be out of scope for Glance.
>            I think Glance should alter its approach to be less generally
>            agnostic about the contents of the objects it hosts. Right now, we
>            are just starting to do this with images, as we slowly advance on
>            offering server side format conversion. We could find similar use
>            cases for single vm templates.
>        The average heat template would provision more than one VM, plus any
>        number of other cloud resources.
>        An image is required to provision a single nova server;
>        a template is required to provision a single heat stack.
>        Hopefully the above "single vm" policy could be reworded to be agnostic
>        to the service which consumes the object that glance is storing.
>    To add to this, is it that Glance wants to be *more* integrated and geared
>    towards vm or container images or that Glance wishes to have more intimate
>    knowledge of the things its cataloging *regardless of what those things
>    actually might be*? The reason I ask is that Glance supporting only "single
>    vm templates" when Heat orchestrates the entire (or almost entire) spectrum
>    of core and integrated projects means that its suitability as a candidate
>    for a template repository plummets quite a bit.
>Yes, I missed the boat a little bit there. I agree Glance could operate as a
>repo for these kinds of templates. I don't know about expanding much further
>beyond the Nova / Heat stack. But within that stack, I think the use cases are
>largely the same.
>It seems like heat templates likely have built-in relationships with vm
>templates / images that would be really nice track closely in the Glance data
>model--for example if you wanted something like a notification when deleting an
>image would invalidate a template you've created. Another advantage is the
>sharing model--Glance is still aiming to become something of an image
>marketplace, and that kind of sharing is something that I see being very useful
>for Heat as well.
>Does this response sound more in line? Sorry I'm still catching up on the
>thread from before it was tagged with [Glance].

FWIW, during last week's meeting, we discussed a bit about image
templates and what they should do. The discussion was oriented to
having support for things like OVF. This sounds like a great
opportunity to expand that concept to something that won't be useful
just for nova but for Heat as well. As Mark mentioned, it's more about
making glance aware about the difference between a template and an
image and their types.

None of this is written on stone. The discussion came out at the
summit and we brought it up at one of our meetings. So, lets make sure
we can cover the required needs.

There's still no blueprint but I created this[0] etherpad where we
could start writing the needs for Heat and other templates.

I agree with Mark. I don't think Glance should expand much further
beyond the Nova / Heat stack and akin.

[0] https://etherpad.openstack.org/p/glance-templates


Flavio Percoco
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