ServiceApplications vs. ServiceApplicationProxies

Question

What exactly is the difference between ServiceApplications (e.g. SearchServiceApplication) and the corresponding ServiceApplicationProxy (e.g. SearchServiceApplicationProxy) ?

• What is the difference
• how do they Play together
• Why is SharePoint (IIS?) build like this?

Answer 1

This might help:

Service Application

This is a logical layer that makes the back-end infrastructure available to the farm. Whenever you use a service application, you do not care about where and how it is exposed. You do not care about the number and location of the physical service instances. You simply access the service application as a logical service.

Service Application Proxy

This is the proxy that virtualizes the access to the service application. In general, it is used on front-end servers of the farm and allows accessing the service application transparently and independently from its actual location.

Source : Paolo Pialorsi, Microsoft® SharePoint® 2010 Developer Reference.

More info on: https://sharepoint.stackexchange.com/a/24012/41443