Best way for two apps on the same machine to communicate

[v1n0]

I have an ASP.NET app running on a webserver. A third party is created another app in PHP which needs to send data to my app for processing.Initially it was assumed that the PHP app would be deployed elsewhere so we agreed that the communication would occur over the internet via HTTP (over SSL). My app would simply use a generic handler (ashx) file to recieve the data and send confirmation back.Now it seems that the PHP app might be deployed on the same machine as my app. I like the fact that using HTTP (as opposed to say direct database access), the PHP app needs to know nothing at all about how my app works. But using the public internet seems silly for communication between two apps on the same machine.If the PHP app simply used a localhost address, would this ensure that all the data stays within the machine? Is there a better way to do this?