Securing Replication Over the Internet
Applies to: 
SQL Server
Azure SQL Managed Instance
Replication over the Internet can provide flexibility, particularly for mobile Subscribers, but you must configure Internet replication appropriately to ensure adequate security. Microsoft recommends using one of two techniques for securely sharing information over the Internet:
Virtual private network (VPN)
The Web synchronization option for merge replication
Virtual Private Network
Virtual private networks provide a simple and secure layered approach to replicating SQL Server data over the Internet. The VPN connection over the Internet logically operates as a Wide Area Network (WAN) link between the sites.
This is achieved by allowing the user to tunnel through the Internet or another public network using a protocol such as Microsoft Point-to-Point Tunneling Protocol (PPTP) available with the Microsoft Windows NT version 4.0 or Microsoft Windows 2000 operating system, or Layer Two Tunneling Protocol (L2TP) available with the Windows 2000 operating system. This process provides security and features similar to those available in a private network.
For more information about setting up a VPN, see the Microsoft Windows documentation.
Web Synchronization Through IIS
The web synchronization option for merge replication provides the ability to replicate data using the HTTPS protocol, which can be a convenient approach to replicating data through a firewall. For more information, see Configure Web Synchronization and Security Architecture for Web Synchronization.