[openstack-dev] [Glance][Glare] External locations design

Fox, Kevin M Kevin.Fox at pnnl.gov
Mon Aug 8 16:33:13 UTC 2016

Has the use case been considered where the compute nodes have no nat to the internet?

The glare api server might have to pass the data through to the requesting client in that case or download/cache an internal copy.

From: Mikhail Fedosin [mfedosin at mirantis.com]
Sent: Monday, August 08, 2016 4:08 AM
To: OpenStack Development Mailing List (not for usage questions)
Subject: Re: [openstack-dev] [Glance][Glare] External locations design

Thanks for you comments Stuart!

I also have some thoughts on this matter: first of all, I never liked how locations are implemented in glance v2, and not just because of inconsistencies in multiple locations per one image, but for the reason that there are no differences between internal and external locations.
So, I think we're on right track with glare's implementation. But I suppose we can improve it even more:  in my understanding, the service generally does not work with external data. I will try to explain with an example:

Let's assume that we have a link to external ubuntu image ( http://releases.ubuntu.com/16.04.1/ubuntu-16.04.1-server-amd64.iso ). When user adds this link to his image artifact, Glare doesn't validate it, it just creates a blob instance in DB (optionally user may specify a checksum).
When user requests 'show' on his image, the blob url will look like this: {"url": "http://releases.ubuntu.com/16.04.1/ubuntu-16.04.1-server-amd64.iso"}, and if user wants to download it, the image won't be proxied with glare - it will be a direct download from ubuntu.com<http://ubuntu.com> from the client.

In case of internal locations their urls are {"url": "/artifacts/images/<image_id>/file"} and these downloads are done with Glare as a proxy between the client and internal cloud storage, like Swift.

For compatibility, internal urls should work with external blobs as well, but there will be a redirect to the external url: "/artifacts/images/<image_id>/file" -> "http://releases.ubuntu.com/16.04.1/ubuntu-16.04.1-server-amd64.iso".

We can discuss it on the artifact meeting at 1730 UTC on Mondays at #openstack-meeting-alt


On Tue, Aug 2, 2016 at 1:16 PM, <stuart.mclaren at hp.com<mailto:stuart.mclaren at hp.com>> wrote:
Hi Kairat,

I think it's great to try and tease through the various issues here.
I added some comments to the etherpad.


Hello all,

I would like to start to describe some design decisions we made in Glare
code (https://review.openstack.org/#/q/topic:bp/glare-api+status:open).  If
you are not familiar with Glare I suggest you to read the following spec:


I hope it will help other folks to understand Glare approach and provide
some constructive feedback for Glare. I think that we can also use Glare
solution for Glance in near future to address some drawbacks we have in

Glare locations

Glance and Glare have possibility to set some external url as
image(artifact) location. This feature is quite useful for users who would
like to refer to some external image or artifact (for example, Fedora image
on official Fedora site) and not to store this image or artifact in the

External locations in Glance have several specialities:


  It is possible to setup multiple locations for an image. Glance uses
  special location strategy to define which location to use. This strategy
  defined in glance codebase and can be configured in glance conf.

  Glance doesn?t differ image locations specified by url and image
  locations uploaded to Glance backend. Glance has some restrictions about
  which urls to use for locations (see Glance docs for more info).

Glare external locations designed in different way to address some
drawbacks we have in Glance. So the approach is the following:


  Glare doesn?t support multiple locations, you can specify dict of blobs
  in artifact type and add url for each blob in dict. User must define a
  name(f.e. region name or priority) for blob in dict and this name can be
  used to retrieve this blob from artifact. So decision about which location
  to use will be outside of Glare.

  Glare adds a special flag to database for external locations. So they
  will be treated differently in Glare when delete artifact. If blob value is
  external url then we don?t need to pass this url to backend and just delete
  the record in DB. For now, Glare allows only http(s) locations set but it
  may be extended in future but the idea still the same: external location
  are just records in DB.

  Glare saves blob size and checksum when specifying external url. When
  user specified url Glare downloads the blob by url, calculates its size and
  checksum. Of course, it leads to some performance degradation but we can
  ensure that the external blob is immutable. We made this because security
  seems more important for Glare than performance. Also there are plans to
  extend this approach to support subscriptions for external locations so we
  can increase secureness of that operation.

I think that some of the features above can be implemented in Glance. For
example, we can treat our locations as only read-only links if external
flag will be implemented.  It will allow us to ensure that only blobs
uploaded through the Glance will be managed.

Additionally, if we will calculate checksum and size for external urls, we
can ensure that  all multiple locations refers to the same blob. So
management of multiple locations(deletion/creation) can be more secure.
Also we can ensure that the external url blob was not changed.

I understand that we need a spec for that but I would like to discuss this
at high level first. Here is etherpad for discussion:

Best regards,
Kairat Kushaev
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