Open Stack

>> 1. Nova bootstrap will be called and it will perform db-migration. Since
>> current approach to nova code is add-only we shouldn't need to stop
>> services and old services should keep working on newer database. Also
>> for minor version upgrades there will be no action here unless there is
>> migration.
>> 2. We upgrade all conductor at the same time. This should take mere
>> seconds since we'll have prebuilt containers
>> 3. We will upgrade rest of controller services with using "series: 1" in
>> ansible to ensure rolling upgrades.

Technically, 2 and 3 need to go at the same time. We have some machinery
in place to help us not do online data conversions until all the control
services are upgraded, but we haven't been through one of those yet to
prove it out. Since the rest of the control services are mostly
stateless, I would recommend just squashing those two steps together for
the time being.

>> 4. We will upgrade all of nova-compute services on it's own pace.

Don't forget the final step of unpinning everyone's compute rpc version
once you're done. If you're using version=auto for compute, you will
soon be able to SIGHUP the services to get them to recalculate the
version pin without restarting.

https://review.openstack.org/#/c/253696/

--Dan