Open Stack

> Glance and Keystone do not participate in a rolling upgrade, because
> Keystone and Glance do not have a distributed component architecture.
> Online data migrations will reduce total downtime experienced during an
> *overall upgrade procedure* for an OpenStack cloud, but Nova, Neutron and
> Cinder are the only parts of OpenStack that are going to participate in a rolling
> upgrade because they are the services that are distributed across all the
> many compute nodes.

Hi Jay,
I'd like to better understand why your definition of rolling upgrades excludes Glance and Keystone? Granted they don't run multiple disparate components over distributed systems, however, they can still run the same service on multiple distributed nodes. So a rolling upgrade can still be applied on a large cloud that has, for instance 50 Glance nodes.  In this case different versions of the same service will run on different nodes simultaneously.
Regards,
Alex