@Roger YoungThe Remote Process Group (RPG) is not designed for dynamic target URL assignment. It is designed to communicate with a target standalone of NiFi cluster. During that communication it learns about all currently connected nodes in a target Nifi cluster and retains the URLS for all those nodes so it can perform a load-balanced delivery of data. It the event RPG cannot get an updated listing form the target it will continue to try to delivery to the last known set of target nodes. Since the RPG was never intended to be used to delivery data to multiple independent target NiFi instances, the ideal of dynamic URL was never considered.
There are other NifI processors such as putHTTP and InvokeHTTP that can take NiFi Expression Language (EL) as input for the target URL.
Thank you,
Matt