What is the best way to migrate data (objects) between two Swift Cluster?

Hi,
I am looking for a way to migrate data (millions of objects) from an existing Openstack Swift Cluster to a new One.
The first Cluster is based on a native Openstack Swift.
The new Cluster is based on a Ceph Rados Gateway integrated to Openstack Swift.
Download containers and import is not an option.

I am trying container-to-container synchronisation, but mapping to the new cluster's container is failling with the error:
ClientException: Container POST failed: http://cluster1:8080/v1/AUTH_c94d038041884a6e8b1235a70635d7fe/cont1 400 Bad Request [first 60 chars of response] Invalid host 'cluster-ceph' in X-Container-Sync-T

Regards!