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 Icehouse yum repository.
Perform a complete upgrade of all packages:
# yum upgrade
Perform database schema upgrades for all of your services.
Review newly installed configuration files.
The upgraded packages will have installed .rpmnew files
appropriate to the Icehouse version of the service. In general,
the Icehouse services will run using the configuration files from
your Havana deployment. The following services will need manual
configuration before they will work correctly: