I have a 10.1 install of galera cluster running in master master mode, i would like to upgrade to 10.2.9, and have seen the instructions here[1] about "regular" updates, but i'd like to keep the cluster online while i upgrade.  Is there any difference or things to look out for to keep data consistency.  can a 10.2 node replicate to a 10.1 node (my guess would be no due to the new fields after mysql_upgrade)  Downtime offline is a possibility, but i'd like to avoid it, as would anyone.