There are two types of classic clusters that are used in Replication Manager service, namely Cloudera Distribution of Hadoop (CDH) and Hortonworks Data Platform (HDP).
These clusters are primarily on-Premise clusters and they must be registered on the Management Console before they can be used for data migration purposes. Any HDP on-premise cluster must be managed by Apache Ambari and enabled for Replication Manager through Cloudera Data Platform. Similarly, CDH on-premise cluster must be managed by Cloudera Manager and enabled for Replication Manager through Cloudera Data Platform. For more information, see Managing classic clusters.