[ceph-users] Setting hostnames for zonegroups via cephadm / rgw mgr module?

Hi, I'm using reef (18.2.2); the docs talk about setting up a multi-site setup with a spec file e.g. rgw_realm: apus rgw_zonegroup: apus_zg rgw_zone: eqiad placement: label: "rgw" but I don't think it's possible to configure the "hostnames" parameter of the zonegroup (and thus control what hostname(s) the rgws are expecting to serve)? Have I missed something, or do I need to set up the realm/zonegroup/zone, extract the zonegroup json and edit hostnames by hand? Thanks, Matthew