2018-03-01 21:06:17,923 WARN [Timer-Driven Process Thread-1] o.a.n.r.util.SiteToSiteRestApiClient Failed to get controller from https://hostname:9443/nifi-api due to org.apache.http.conn.HttpHostConnectException: Connect to hostname:9443 [hostname/xx.xx.xx.xx] failed: Connection timed out: connect
Have you verified that there are no firewalls between your local instance and the target instance?
I see that your target instance is secured. Is your local instance secured as well? A 2-way TLS handshake is going to be required to communicate with a secured target NiFi. This means you need to make sure that each instance is capable of trusting the certificate presented by the other in the handshake.
Perhaps enabling ssl debug on the target NIFi will provide more insight here.
add following in bootstarp.conf file:
The ssl handshake that occurs between the system will be logged in the nifi-bootstrap.log