Open Stack

Hello!

As you may know glance v1 is going to be deprecated in Newton cycle. Almost
all projects support glance v2 at this moment, Nova uses it by default.
Only one thing that blocks us from complete adoption is a possibility to
set custom locations to images. In v1 any user can set a location to his
image, but in v2 this functionality is not allowed by default, which
prevents v2 adoption in services like Horizon or Heat.

It all happens because of differences between v1 and v2 locations. In v1 it
is pretty easy - user specifies an url and send a request, glance adds this
url to the image and activates it.
In v2 things are more complicated: v2 supports multiple locations per
image, which means that when user wants to download image file glance will
choose the best one from the list of locations. It leads to some
inconsistencies: user can add or delete locations from his image even if it
is active.

To enable adding custom locations operator has to set True to config option
'show_multiple_locations'. After that any user will be able to add or
remove his image locations, update locations metadata, and finally see
locations of all images even if they were uploaded to local storage. All
this things are not desired if glance v2 has public interface, because it
exposes inner cloud architecture. It leads to the fact that Heat and
Horizon and Nova in some cases and other services that used to set custom
locations in glance v1 won't be able to adopt glance v2. Unfortunately,
removing this behavior in v2 isn't easy, because it requires serious
architecture changes and breaks API. Moreover, many vendors use these
features in their clouds for private glance deployments and they really
won't like if we break anything.

So, I want to hear opinions from Glance community and other involved people.

Best regards,
Mikhail Fedosin
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