On all of your hosts:
If you are running Puppet as configured by Staypuft, you must disable it:
# systemctl stop puppet
# systemctl disable puppet
This ensures that the Staypuft-configured puppet will not revert changes made as part of the upgrade process.
Install the Juno yum repository.
Upgrade the openstack-selinux package, if available:
yum upgrade openstack-selinux
This is necessary to ensure that the upgraded services will run correctly on a system with SELinux enabled.