What are some good ways to do this? Is it even possible to do cleanly?
Ideally I\'d like to use packet headers to decide which server should handle requests. Howeve
Either two different IP addresses (like recommended) or one web server is reverse-proxying the other (which is listening on a port <>80).
For instance: Apache listens on port 80, IIS on port 8080. Every http request goes to Apache first (of course). You can then decide to forward every request to a particular (named virtual) domain or every request that contains a particular directory (e.g. http://www.example.com/winapp/) to the IIS.
Advantage of this concept is that you have only one server listening to the public instead of two, you are more flexible as with two distinct servers.
Drawbacks: some webapps are crappily designed and a real pain in the ass to integrate into a reverse-proxy infrastructure. A working IIS webapp is dependent on a working Apache, so we have some inter-dependencies.