I'm a little confused by your original post but let me try to summarize what I think you're asking...
- Application A resides (logically) behind a reverse proxy
- Application A could be accessed directly by calling http://RealAppHost:RealPort/appPath/appName
- Users access this application be calling something like http://RpHost:RpPort/appPath/appName
- Within Application A, you need to make a call to Application B which resides on the same host
- You're unable to get the real host name using a getServerName call when using the app through RP
For starters, everything seems to be functioning as it should... you don't want folks accessing your apps to get the real server name whenever they request it. They should always get the RP name, that's one of the reasons you use RPs.
You've said "I have an app..." and "...my app is deployed" Are you the app developer? Lacking further details, I see a very simple solution... how do you deploy your applications? Whatever tool you're using must be connected to that application host to deploy your app so a quick examination of that tool's settings should give you the host name. Alternatively, there must be a member of the Basis or Network Security teams at your office that support those reverse proxies who could quickly examine the rewrite statements in use and give you the host name and port of the application host.
What for of reverse proxy are you using... Apache? ...Web Dispatcher? ...or?
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