[openstack-dev] [tc] [all] [glance] Answers to some questions about Glance

John Griffith john.griffith8 at gmail.com
Tue May 17 14:02:47 UTC 2016

Thanks Brian

On Tue, May 17, 2016 at 6:54 AM, Brian Rosmaita <
brian.rosmaita at rackspace.com> wrote:

> Subject was: Re: [openstack-dev] [tc] [all] [glance] On operating a high
> throughput or otherwise team
> Un-hijacking the thread.  Here are some answers to John's questions, hope
> they are helpful.
> On 5/16/16, 9:06 PM, "John Griffith" <john.griffith8 at gmail.com> wrote:
> Hey,
> Maybe not related, but maybe it is.  After spending the past couple of
> hours trying to help a customer with a Glance issue I'm a bit... well
> annoyed with Glance.  I'd like to chime in on this thread.  I'm honesty not
> entirely sure what the goal of the thread is, but honestly there's
> something rather important to me that I don't really seem to see being
> called out.
> Is there any way we could stop breaking the API and it's behaviors?  Is
> there any way we can fix some of the issues with respect to how things work
> when folks configure multiple Glance repos?
> Couple of examples:
> 1. switching from "is_public=true" to "visibility=public"
> This was a major version change in the Images API.  The 'is_public'
> boolean is in the original Images v1 API, 'visibility' was introduced with
> the Images v2 API in the Folsom release.  You just need an awareness of
> which version of the API you're talking to.
> Ok, cool, I'm sure there's great reasons, but it really sucks when folks
> update their client and now none of their automation works any longer
> The Images v1 API went from CURRENT to SUPPORTED in the Kilo release
> (April 30, 2015).  The python-glanceclient began using v2 as the default
> with Change-Id: I09c9e409d149e2d797785591183e06c13229b7f7 on June 21, 2015
> (and hence would have been in release 0.17.2 on July 16, 2015).  So these
> changes have been in the works for a while.
> 2. making virtual_size R/O
> So for some time this was a property that folks could use to set the size
> of an image needed for things like volume creation, cloning etc.  At some
> point though it was decided "this should be read only", ok... well again
> all sorts of code is now broken, including code in Cinder.​  It also seems
> there's no way to set it, so it's always there and just Null.  It looked
> like I would be able to set it during image-create maybe... but then I hit
> number 3.
> The virtual_size was added to the Images v2 API with Change-Id:
> Ie4f58ee2e4da3a6c1229840295c7f62023a95b70 on February 11, 2014.  The commit
> message indicates: "This patch adds the knowledge of a virtual_size field
> to Glance's API v2. The virtual_size field should respect the same rules
> applied to the size field in terms of readability, access control and
> propagation."  The 'size' field has never been end-user modifiable, hence
> the virtual_size is read-only as well.
> 3. broken parsing for size and virtual_size
> I just started looking at this one and I'm not sure what happened here
> yet, but it seems that these inputs aren't being parsed any more and are
> now raising an exception due to trying to stuff a string into an int field
> in the json schema.
> Please file a bug with some details when you know more about this one.  It
> sounds like a client issue, but you can put details in the bug report.
> So I think if the project wants to move faster that's great, but please is
> theres any chance to value backwards compatibility just a bit more?​  I'm
> sure I'm going to get flamed for this email, and the likely response will
> be "you're doing it wrong".  I guess if I'm the only one that has these
> sorts of issues then alright, I deserve the flames, and maybe somebody will
> enlighten me on the proper ways of using Glance so I can be happier and
> more in tune with my Universe.
> Well, since you asked for enlightenment ... it *is* helpful to make sure
> that you know which version of the Images API you're using.  The Glance
> community values backwards compatibility, but not across major releases.
> As I imagine you're aware, Glance is tagged "release:
> cycle-with-milestones", so you can read about any changes in the release
> notes.  Or if you want a quick overview of what major features were added
> to Glance for each release, there was an excellent presentation at the
> Tokyo summit about the evolution of the Glance APIs:
> https://www.openstack.org/summit/tokyo-2015/videos/presentation/the-evolution-of-glance-api-on-the-way-from-v1-to-v3
> slides only:
> http://www.slideshare.net/racker_br/the-evolution-of-glance-api-on-the-way-from-v1-to-v3
> Before people begin freaking out at the mention of the Images v3 API,
> please note that the presentation above described the state of Glance as of
> October 2015.  The Glance documentation has a statement about the two
> Images APIs and the current plans for The Future that was updated shortly
> after the Austin summit:
> http://docs.openstack.org/developer/glance/glanceapi.html#glance-and-the-images-apis-past-present-and-future
> (Spoiler alert: no plans for Images v3 API at this point.)
> Thanks,
> John
> Hope that was helpful,
> brian
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