First off, I am an amateur to Openstack upgrading and made a big mistake in upgrading the controller and compute nodes OS from Ubuntu 16.04 to 18.04. I know now that was a mistake. My Openstack Pike fails now.
Is there a step by step procedure to undo what I did in reference to the 16.04 to 18.04 upgrade?
Don
In practice downgrading Ubuntu from major release is not possible [1], however in theory, you could re-tweak apt source files to point to the previous release [2], some packages have deb-postinst scripts which might migrate the config files, so downgrading might cause service to fail, etc.., thus requiring more manual work to fix the config.
IMO, your best option at moment is to try and fix the issues with Openstack, for that, more details are needed, like: which Openstack distro (Mirantis, Red Hat, Ubuntu, etc..) and the errors you are seeing (logs, etc...)
[1] https://askubuntu.com/questions/49869/how-to-roll-back-ubuntu-to-a-previous-version
