[Users] Command line : how to add a removed host?

Hi, Doing some tests, I set 2 hosts into maintenance mode, then "removed" them. When trying to add them back into the cluster, I found nothing more than the "new" action. Using it and configuring the IP address, I see oVirt re-installing many packages. Once installed, the host can not be added because : "Host host016 is installed with VDSM version (4.13) and cannot join cluster cluster21 which is compatible with VDSM versions [4.9, 4.11, 4.12, 4.10]." In fact, I have 2 questions: - For the second host (still untouched), is there a way to add it back into the cluster without re-installing the packages maybe via the command line) (and then preventing this version issue)? - For the weeks to come, I see I'll have to upgrade some parts. I don't know what is needed to upgrade for the VDSM version to get upgraded ("for [4.9, 4.11, 4.12, 4.10] to increase"). Obviously, I don't want to break the whole cluster while upgrading it. Thank you. -- Nicolas Ecarnot