I will be upgrading the physical host machines to Ubuntu 18.10 early Saturday morning.  The upgrade process is rather long and grueling and during at least part of it breaks NIS.  However, these machines are all NIS slaves and I will time the upgrades such that only one will be affected at any given time so all of the client machines should be okay.  However, all will go down several times during the upgrade process,  Normally Linux upgrades require only a single reboot however to work around bugs in the upgrade process regarding NIS, it will be necessary to de-install / re-install nis and reboot possibly more than once.  So there may be multiple outages between 12:01 – 6:00 AM on Saturday the 27th.  This upgrade is important as it fixed the issue of NFS not mounting reliably at least with all the machines with modern kernels.  It will not fix the old CentOS 6 machine that everyone loves however.