Posted by Rule #1: Drain the worker node before a reboot.
Consequences if you do not follow the Rule #1: the mongo-db gets corrupt and you need to repair it.
Steps to repair the customizer DB: delete the contents in mongo-node-0, mongo-node-1 and mongo-node-2’s subdirectory /data/db/ and register the customizer apps in the appregistry again.
I’m sure that there’s a way to repair the mongo db directories…