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On 13:07 Aug 07, Jay Pipes wrote:
> Hi Nik, some comments inline, but tl;dr I am strongly against
> returning the glance_store library to the Glance source repository.
> Explanations inline...
> 
> On 08/07/2015 01:21 AM, Nikhil Komawar wrote:
> >Hi,
> >
> >During the mid-cycle we had another proposal that wanted to put back the
> >glance_store library back into the Glance repo and not leave it is as a
> >separate repo/project.
> >
> >The questions outstanding are: what are the use cases that want it as a
> >separate library?
> >
> >The original use cases that supported a separate lib have not had much
> >progress or adoption yet.
> 
> This is really only due to a lack of time to replace the current
> nova/image/download/* stuff with calls to the glance_store library.
> It's not that the use case has gone away; it's just a lack of time to
> work on it.

When Cinder wanted to integrate os-brick (initiator code library) into Nova,
Cinder folks integrated it themselves [1]. Has anyone from Glance been spending
the time to do this? If so, are there reviews you can give so we can see why
things are blocked?

> > There have been complaints about overhead of
> >maintaining it as a separate lib and version tracking without much gain.
> 
> I don't really see much overhead in maintaining a separate lib,
> especially when it represents functionality that can be used by
> Cinder and Nova directly.

As mentioned earlier Cinder is doing os-brick for both Cinder and Nova to
consume. Other projects are planning to use it as well, and it has been a huge
win to take some complications from other projects that aren't focusing on
block storage like we are. I recommend creating a gerrit dashboard [2] to
include a separate library with Glance reviews. I'm also not sure of what
overhead there could be besides having do release.

<snip>

> >4. cleaner api / more methods that support backend store capabilities -
> >a separate library is not necessarily needed, smoother re-factor is
> >possible within Glance codebase.
> 
> So, here's the crux of the issue. Nova and Cinder **do not want to
> speak the Glance REST API** to either upload or download image bits
> from storage. Streaming image bits through the Glance API endpoint is
> a needless and inefficient step, and Nova and Cinder would like to
> communicate directly with the backend storage systems.
> 
> glance_store IS the library that would enable Nova and Cinder to
> communicate directly with the backend storage systems. The Glance API
> will only be used by Nova and Cinder to get information *about* the
> images in backend storage, not the image bits themselves.

+1

Provide a way to talk to the implementation, and step out of the way to let it
do what it does best. This is no different than other Openstack projects.

In Cinder, image copying to a volume is a huge problem today. We have a Cinder
glance_store [2] that is being revived to leave the images stored in the block
storage backends themselves, which, oh my goodness is using os-brick!!

The block storage backends know how to do efficient image copying/cloning to
their volumes, not Glance.


[1] - https://review.openstack.org/#/c/175569/
[2] - https://review.openstack.org/#/c/166414/

-- 
Mike Perez