The 3.5.x Zookeeper properties file has changed:
As a result, the current embedded zookeeper bundled with NiFi will require a minor change to the zookeeper.properties file. We could potentially do this automatically by removing the clientPort line and appending the value to the end of the server string/s.
The assumption here would be that the client port is currently configured the same across all servers. If not, we would not be able to auto-migrate the change, and we would need to fail the start and get the user to configure the zookeeper.properties file correctly across all nodes.