@Willian Gosse - During a NiFi restart, the flow is loaded and started before the NiFi UI is made available. During this period of time the Remote Process Groups (RPG) on each node will fail to be able to connect to the configured target NiFi URL to fetch the Site-To-Site (S2S) details. This is expected behavior. The RPGs will stop throwing this error in the logs once the configured target NiFi URL is made available and the S2S details are successfully retrieved. - The use of HTTP or RAW as the transport protocol controls how the actual FlowFiles are transferred. The re-occurring connection to retrieve the S2S details will always be over http to the target NiFi URL configured in the RPG. When using HTTP transport protocol. the NiFi FlowFiles will also be transferred via the same HTTP port as the Target NiFi UI is exposed on. Setting transport protocol to use RAW causes the RPG to use a dedicated socket port for the FlowFile transfer. The socket port used is set by the target NiFi servers in the nifi.properties file (property: nifi.remote.input.socket.port=). The advantage to using RAW is that amount of traffic going to HTTP port used to access UI is reduced considerably. The advantage to using HTTP is that you have one less port you must open through any firewalls to the NiFi nodes. - Thank you, Matt - If you found this answer addressed your question, please take a moment to login in and click the "ACCEPT" link. ... View more