In this scenario, you will take down all of your OpenStack services at the same time, and will not bring them back up until the upgrade process is complete.
On all of your hosts:
Install the Kilo yum repository.
Perform a complete upgrade of all packages:
# yum upgrade
Perform any necessary configuration updates for each of your services.
Perform database schema upgrades for each of your services:
Review newly installed configuration files.
The upgraded packages will have installed .rpmnew files
appropriate to the Kilo version of the service. In general,
the Kilo services will run using the configuration files from
your Juno deployment, but you will want to review the
.rpmnew files for any required changes.
New versions of OpenStack services may deprecate certain configuration options. You should also review your OpenStack logs for any deprecation warnings, because these may cause problems during a future upgrade.