There are many challenges to overcome if you wish to externally expose a WCF service hosted on premise. You will need to potentially make changes to some or all of these infrastructure components within your environment: NAT, routers, hardware firewalls, and software firewalls.

Normally, a reverse proxy server would be used and firewall rules would be created to expose a WCF service. The following diagram shows the typical network infrastructure required to expose a service externally to the Internet:

However, with the introduction of Azure Service Bus Relays, there is no requirement for proxy or firewall changes, provided outbound ports are open for HTTPS traffic. Effectively, the endpoint in Azure would be exposed to the outside world and not the endpoint locally on your server.

Here is how you would typically expose an on-premise WCF service using Relays in Azure:

Endpoints based on WCF relay bindings open an outbound connection to Azure. Once this connection is established...