Description of problem:


Documentation on https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/9/html/upgrading_red_hat_openstack_platform/chap-upgrading_the_environment talks about upgrades, but it's always assuming that the user will be on a system using RHEL subscription.
It is very usual for production systems, to don't rely on RHEL CDN, but have pre-built local mirrors. And documentation on upgrades does not mention anything about it.

Two different points shall be modified here. First, the one that comments on how to upgrade undercloud:

$ sudo subscription-manager repos --disable=rhel-7-server-openstack-8-rpms --disable=rhel-7-server-openstack-8-director-rpms
$ sudo subscription-manager repos --enable=rhel-7-server-openstack-9-rpms --enable=rhel-7-server-openstack-9-director-rpms

Could be mentioned here, to disable local repos for 8, and enable the repos for 9, in case of local mirrors.

Also, not as obvious as the first one. The system does the upgrade from 8 to 9 on that step:

$ openstack overcloud deploy --templates \
  --control-scale 3 \
  --compute-scale 3 \
  -e /usr/share/openstack-tripleo-heat-templates/environments/network-isolation.yaml \
  -e /usr/share/openstack-tripleo-heat-templates/environments/net-single-nic-with-vlans.yaml  \
  -e /home/stack/templates/network_env.yaml \
  -e /usr/share/openstack-tripleo-heat-templates/environments/major-upgrade-pacemaker-init.yaml

This relies on UpgradeInitCommand parameeter, to know which repos to disable and which ones to enable. By default, just assumes that the nodes are registered and using repos from CDN, and just disables 8 and enables 9.
But in the case of local mirrors, this parameter needs to be customized, to achieve all this repo change. Upgrade documentation shall talk about it, giving some example.