From http://lists.openstack.org/pipermail/openstack-dev/2015-June/067795.html :

"""

There was a bug raised [1] from some large deployments that the Cinder
client 1.2.0 and beyond is not working because of version discovery.
Unfortunately it's not taking into account of deployments that have a
proxy.

Cinder client asks Keystone to find a publicURL based on a version.
Keystone will gather data from the service catalog and ask Cinder for
a list of the public endpoints and compare. For the proxy cases,
Cinder is giving internal URLs back to the proxy and Keystone ends up
using that instead of the publicURL in the service catalog. As a
result, clients usually won't be able to use the internal URL and
rightfully so.

This is all correctly setup on the deployer's side, this an issue with
the server side code of Cinder.

There is a patch that allows the deployer to specify a configuration
option public_endpoint [2] which was introduced in a patch in Kilo
[3]. The problem though is we can't expect people to already be
running Kilo to take advantage of this, and it leaves deployers
running stable releases of Juno in the dark with clients upgrading and
using the latest.

"""


The implication is that we may have a problem for users who upgrade to the latest cinderclient and try to use it with a Juno (6.0) deployment.

The 7.0 python-cinderclient branch is currently based on 1.2.1.