Please update "8.7. Creating the Overcloud with Pre-Provisioned Nodes" [1] of the document Director Installation and Usage (An end-to-end scenario on using Red Hat OpenStack Platform director to create an OpenStack cloud) to add a few steps missing when deploying Ceph in the overcloud or deploying an overcloud to use an external Ceph cluster. 

The document is missing something like the following: 

"""
When using ceph-ansible and Using Already Deployed Servers, it is necessary to run commands like the following from the undercloud before deployment:

export OVERCLOUD_HOSTS="192.168.1.8 192.168.1.42"
bash /usr/share/openstack-tripleo-heat-templates/deployed-server/scripts/enable-ssh-admin.sh
for h in $OVERCLOUD_HOSTS ; do
    ssh $h -l stack "sudo groupadd ceph -g 64045 ; sudo useradd ceph -u 64045 -g ceph"
done

In the example above, the OVERCLOUD_HOSTS variable should be set to the IPs of the overcloud hosts which will be Ceph clients (e.g. Nova, Cinder, Glance, Gnocchi, Manila, etc.). The enable-ssh-admin.sh script configures a user on the overcloud nodes that Ansible uses to configure Ceph clients. The for loop creates the Ceph user on the relevant overcloud hosts.
"""

The above is from the upstream documentation which was recently updated [2]. 

Without this change it's possible to run into what's described in bug 1536678 [3]. 

Also, the above steps include adding the Ceph user to the overcloud nodes. This step won't be necessary after BZ 1546233 is resolved. 


[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/12/html/director_installation_and_usage/chap-configuring_basic_overcloud_requirements_on_pre_provisioned_nodes#sect-Creating_the_Overcloud_with_Pre_Provisioned_Nodes

[2] https://review.openstack.org/#/c/545460/

[3] https://bugzilla.redhat.com/show_bug.cgi?id=1536678

[4] https://bugzilla.redhat.com/show_bug.cgi?id=1546233