Ceph clusters use a service called the Ceph Object Gateway to provide the Swift and S3 interface to clients. This service is commonly referred to as radosgw.
https://docs.ceph.com/en/reef/radosgw/
Unlike the osd,mon, mds and mgr services, which are Ceph cluster internal daemons, radosgw is different in that it is just a client application.
In our case, each of our OSD servers is also going to run a radosgw daemon.