cinder, cinder-ceph and ceph-mon are related to offer a cinder backend for OpenStack. To backup data from the cluster, I'd like to use cinder-backup and relate to a separate cluster named ceph-mon-backup instead of the original ceph cluster.
In that case, cinder will have one /etc/ceph/ceph.conf and it has only one "mon host" line of the original cluster.
cinder-backup charm should set "backup_ceph_conf = /var/lib/charm/cinder-backup/ceph.conf" line in cinder.conf to use a different cluster and "mon host".
https://docs.openstack.org/ocata/config-reference/block-storage/backup/ceph-backup-driver.html
[/etc/cinder/cinder.conf]
...
backup_driver = cinder.backup.drivers.ceph
backup_ceph_pool = cinder-backup
backup_ceph_user = cinder-backup
...
root@juju-111d21-6-lxd-1:~# ll /etc/ceph/ceph.conf
lrwxrwxrwx 1 root root 27 Aug 28 05:35 /etc/ceph/ceph.conf -> /etc/alternatives/ceph.conf
root@juju-111d21-6-lxd-1:~# ll /etc/alternatives/ceph.conf
lrwxrwxrwx 1 root root 36 Aug 28 05:35 /etc/alternatives/ceph.conf -> /var/lib/charm/cinder-ceph/ceph.conf
root@juju-111d21-6-lxd-1:~# ll /var/lib/charm/*/*
-rw-r--r-- 1 root root 453 Aug 28 12:35 /var/lib/charm/cinder-backup/ceph.conf
-rw-r--r-- 1 root root 455 Aug 28 05:37 /var/lib/charm/cinder-ceph/ceph.conf
test bundle