I have Graylog 2.1.2 cluster on ubuntu 14.04, with 2 collectors and 4 elastic data nodes and monitor.
what i want to do is to upgrade each machine separate from Graylog 2.1.2 to 2.2.3 and rejoin her to the cluster.
My question is when i do a single machine upgrade from 2.1.2 to 2.2.3 and rejoin the machine back to the cluster with 2.1.2 version machines, will the system work properly with differences in version of graylog? differences in versions of elasticsearch? if there is any mitigation or recommendation for upgrading cluster without having downtime.
My second question is the same as before but i wonder about OS upgrade from ubuntu 14.04 to 16.04, will it work properly too?