Hi Mark, I have a similar use case where we need to upgrade both Jenkins and the OS (from OEL7 to OEL8). Do you recommend that the OS is upgraded first or Jenkins?
I’d install a fresh machine with the target OEL8 operating system first, then install Jenkins using the RPM install instructions and restore the old Jenkins home directory onto the new machine. That makes the new machine a safe place to verify that the restore from backup worked and that Jenkins is running as expected on the new machine, while leaving the previous machine to support users until you’re ready to switch to the new machine.