Comment 60 for bug 1719436

I was running in to this too and couldn't figure out why - juju's status output was stuck on "Bootstrapping MON cluster" and the ceph-mon(s) themselves were logging messages regarding probing/electing.

Ultimately the cause in this case was too large an MTU on the underlying VLAN interface that the LXD container used. After reducing down to an MTU of 9000 from 9216, I was able to bootstrap the ceph-mon cluster.

This isn't technically related to this bug, but given this is one of the most popular results on Google for "Bootstrapping MON cluster", it may help someone in the future.