I work with Gary and we were able to complete this leapp upgrade, with a few small alterations to the documented steps. We are using the documentation on the page @evgeni provided (silly us for not seeing that page before).
Fortunately, this was all done in our lab environment, so we were able to do it many times to get it right, reverting back to snapshots whenever we ran into major issues that we figured out how to fix.
First change was after leeap upgrade and before the reboot. Since this server was subscribed to foreman before, we had to remove the redhat.repo file so during the Rocky 8 upgrade, it wouldn’t fail looking for repos it would never find. We probably could have (should have?) just run subscription-manager remove, but we just removed the repo file instead.
Next, the doc has dnf module enable katello:el8 pulpcore:el8 long after the server comes back up after the reboot. However, the leapp upgrade would fail during foreman-installer.
Also, for some reason, when the upgrade copied files from /var/opt/rh/rh-postgresql12/lib/pgsql/data/ to /var/lib/pgsql/data/, they became owned by root, not postgres.
So what we ended up doing was immediately after the server booted back up into Rocky 8, I quickly logged in and ran, before leapp continued and began foreman-installer:
chown -R postgres:postgres /var/lib/pgsql/data
dnf module enable katello:el8 pulpcore:el8 foreman:el8 -y
That allowed leapp upgrade to complete successfully.
I ran into an issue during runuser -u postgres -- reindexdb -a,
reindexdb: error: reindexing of database "foreman" failed: ERROR: could not create unique index "index_fact_names_on_name_and_type"
DETAIL: Key (name, type)=(ssh::rsa::key, PuppetFactName) is duplicated.
but that was quickly resolved from this forum page - reindexdb: error
And lastly, though this doesn’t really have anything to do with leapp upgrade, we had to disjoin and rejoin the freeipa domain.
But now, we have a fully functional Foreman/Katello server upgraded from CentOS 7 to Rocky 8. This is going to really save our bacon if we can get this to work on our Production servers!