What is Windows Process Activation Service? Windows Process Activation Service, also referred to as WAS, is a new component in IIS 7.0 that manages application pool configuration and worker processes instead of the WWW process. This enables the same configuration for both HTTP and non-HTTP sites to be used. Thanks to this separation (and in combination with the new modular architecture of IIS 7.0), you can even host non-HTTP sites without the WWW Service even being installed in the first place.
How does Windows Process Activation Service work? Taken directly from the documentation:
“The WAS process model generalizes the IIS 6.0 process model for the HTTP server by removing the dependency on HTTP. This allows WCF services to use both HTTP and non-HTTP protocols, such as Net.TCP, in a hosting environment that supports message-based activation and offers the ability to host a large number of applications on a given machine."
What scenarios does this enable? Since WAS is not specific to HTTP sites, you can use WAS to host non-HTTP sites as well. But what do we mean by “non-HTTP sites?” Well, simply put, WAS can be used to host sites built on technologies like Windows Communication Foundation, for example. If you are using WCF with WAS, are you limited to listening over HTTP? Not at all. In fact, that is the beauty and power of WAS. You can be hosting a WCF service within WAS that is using a netTcpBinding, netMsmqBinding, etc. As an extension to this, since WAS supports both HTTP and non-HTTP sites, this also means that you can be hosting a service that exposes itself over both HTTP and NET.TCP as well.