As I’v read and thought a lot about the migration as this is a bigger project, I was wondering if anyone has done that already and might share some notes or playbooks, because in all readings there where some parts missing or miss understandable to me.

I do have some different approaches in mind, so may be you have some suggestions or hints.

a) upgrade nautilus on centos 7 with the few missing features like dashboard and prometheus. After that migrate one node after an other to ubuntu 20.04 with octopus and than upgrade ceph to the recent stable version.

b) migrate one node after an other to ubuntu 18.04 with nautilus and then upgrade to octupus and after that to ubuntu 20.04.

or 

c) upgrade one node after an other to ubuntu 20.04 with octopus and join it to the cluster until all nodes are upgraded.

For test I tried c) with a mon node, but adding that to the cluster fails with some failed state, still probing for the other mons. (I dont have the right log at hand right now.)

So my questions are:

a) What would be the best (most stable) migration path and

b) is it in general possible to add a new octopus mon (not upgraded one) to a nautilus cluster, where the other mons are still on nautilus?

I hope my thoughts and questions are understandable :)

Thanks for any hint and suggestion. Best . Götz