RPC over HTTPS connecting to a cluster of back-end only servers

Clarifications

In order to properly setup RPC over HTTP(s), you will need front end servers running both IIS web services and the RPC over HTTP proxy service, as well as being setup in an NLB cluster if you want then to load balance web traffic. The front end servers act as proxy/gateways to the backend servers and take the front end traffic and relay it to the back end servers running the information store over native RPC calls. You can't have a backend server also be a front end server, but it can be an RPC over HTTP proxy, but that in itself defeats the purpose of a front end/back end design for security. Usually, a front end server is in a DMZ or perimiter network and the only traffic allowed through the firewall to the backend is HTTP(s) and RPC to name a few. The front end servers should only accept HTTP(s) traffic and nothing else from the web. Yes, your client is technically right in a sense, but is wrong in the security sense because I have not seen any sane person set it up the way they propose without exposing the information store to malicious attacks from the web. Microsoft has entire white papers on setting up clustered Exchange in a FE/BE scenario and I myself have deployed Exchange clusters in accordance with the whitepaper and MS recommendations.