I wanted to add that when using the IP address:104.36.197.137 of sftp.uber.com it worked with NiFi 2.9.0 using PROXY HTTP Configuration service.   It has nothing to do with the OS DNS resolution because it is connected to the proxy server to resolve the destination. When using sftp.uber.com, NiFi PROXY HTTP configuration service, it never reached the proxy server at all from the Proxy trace debug.  It has to be a NiFi PROXY configuration resolution with hostname when it works with 1.2x and not 2.x. ... View more