With FlyData Sync, we now offer a new feature called Secure Tunnel as a part of any plans 5MR or above.
Secure Tunnel is an OpenVPN tunnel between our environments and will not require any of your infrastructure to be public. FlyData will provide a Cloudformation template that will launch an instance with the configuration options selected during the Cloudformation setup.
With this in place, you can have everything private and also use our FlyData Direct feature.
For more information on the Cloudformation setup: https://www.flydata.com/resources/amazon-redshift/configuring-cloudformation/