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Hi Gareth,

The swift backend optionally used by glance to store image content is
just one of the stores supported by glance. Alternatively the image
data can be stored in flat files (the default option), S3, RBD-based
stores, or in external stores accessible via HTTP.

In addition to being able to use alternative stores to swift, glance
also manages image metadata independently of the backend, via a local
RDBMS (generally mysql or posrtgresql).

So to answer your question, glance is not just a thin layer over swift.
You could of course re-implement a more limited glance-like image service
in that way, but you would be losing some flexibility and also creating
a maintenance headache for yourself in shadowing developments in the
glance API to avoid breaking clients such as nova & cinder.

Cheers,
Eoghan

----- Original Message -----
> Thanks for your answer, Iccha and Eoghan,
> 
> I have another problem. After scanning the source codes, I found current
> Glance is just managing image file （or disk file）, which I think its
> functionality is subset of Swift. Both x-meta-image-* and
> x-meta-image-property-* could store in Swift metadata, and ACLs could help
> manage authorizing. And some new features like protected properties could be
> implemented as middleware in Swift too. So, I'm not clear about the goal of
> this project.
> 
> Before reading the codes (I have to read codes because Glance documents is
> not so helpful), I image this project could manage image file, and also data
> in this image, such root password, default IP and so on. But it's not real.
> 
> In short, if I want build a cloud with OpenStack and I have ability to write
> my own codes, are there some reasons I setup Glance to manage images, not to
> write a Swift middleware to avoid lots of middle-process?
> 
> 
> 
> 
> On Fri, Apr 12, 2013 at 6:01 PM, Eoghan Glynn < eglynn at redhat.com > wrote:
> 
> 
> 
> 
> > Gareth,
> > 
> > There are a number of improvisations in v2 of Glance API. To name a few the
> > registry layer is no longer been used in v2 of Glance API(so one less layer
> > your request has to go through), image sharing has been designed to prevent
> > spamming in v2, there are additional features like protected properties and
> > multiple locations been worked on. I am sure there are several more.
> 
> 
> One other bit of newness in v2 that's worth noting, because it's
> actually used in anger by both cinder and nova currently, is the
> direct_url metadata which if enabled in glance allows a client to
> directly access image content from the backend store (if that can
> be achieved more cheaply that way than by traversing the glance-api
> service).
> 
> Also there was a design document for the v2 API knocking around
> that might be useful for background and detail. The latest draft
> version I have to hand is:
> 
> https://docs.google.com/document/d/1jPdgmQUzTuSt9iqcgPy74fbkzafCvqfQpvzRhwf2Kic
> 
> though there may be a more recent version in existence.
> 
> Cheers,
> Eoghan
> 
> 
> > Thanks,
> > Iccha
> > 
> > -----Original Message-----
> > From: "Gareth" < academicgareth at gmail.com >
> > Sent: Thursday, April 11, 2013 12:51am
> > To: openstack-dev at lists.openstack.org
> > Subject: [openstack-dev] [Openstack][Glance] difference api version between
> > v1 and v2
> > 
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> > Hi, Glance devs
> > 
> > Any design purpose between v1 and v2 API?
> > 
> > I know the url changed a little, but functionality seems same.
> > 
> > So is there any further improvement in v2 API?
> > 
> > Thanks
> > --
> > Gareth
> > 
> > *Cloud Computing, Openstack, Fitness, Basketball
> > *
> > *OpenStack contributor*
> > *My promise: if you find any spelling or grammar mistakes in my email from
> > Mar 1 2013, notify me *
> > *and I'll donate $1 or ￥1 to an open organization you specify.*
> > 
> > 
> > 
> > _______________________________________________
> > OpenStack-dev mailing list
> > OpenStack-dev at lists.openstack.org
> > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
> > 
> 
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> 
> 
> 
> --
> Gareth
> 
> Cloud Computing, Openstack, Fitness, Basketball
> OpenStack contributor
> My promise: if you find any spelling or grammar mistakes in my email from Mar
> 1 2013, notify me
> and I'll donate $1 or ￥1 to an open organization you specify.
> 
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>