The two nodes of the cluster hide behind the GW. All of the ordinary clients are not allowed
to directly access either of the database nodes except the administrator by some specific or
provisional method.

Firwall with DBTwin Active-Active Database Cluster Diagram
For further info,please click the following link:
An Effective Proprietary Database Firewall Based on DBTwin Active-active Database Cluster
https://www.zhetides.com/nd.jsp?id=42