Postgresql: installation, join script

we have a UCS primary domain controller and a managed node, both a fresh installation of UCS-5.0-2.
We wanted Postgresql to run on the pdc and nextcloud on the managed node, using postgresql of the pdc.
Therefore postgresql was installed on the pdc by running

univention-install univention-postgresql-11

After installing nextcloud on the managed node, postgresql got installed there as well.

How to get the managed node to use the postgresql instance of pdc?
Was postgresql installed the right way?
Should a join script for postgresql exist on the pdc (it does not)?