Wednesday, 7 July 2010

What is the Windows Process Activation Service (WAS)?

Here are some brief notes on the Windows Process Activation Service.

“Windows Process Activation Service (WAS) is the new process activation mechanism for the Windows Server 2008 that is also available on Windows Vista. It retains the familiar IIS 6.0 process model (application pools and message-based process activation) and hosting features (such as rapid failure protection, health monitoring, and recycling), but it removes the dependency on HTTP from the activation architecture. IIS 7.0 uses WAS to accomplish message-based activation over HTTP. Additional WCF components also plug into WAS to provide message-based activation over the other protocols that WCF supports, such as TCP, MSMQ, and named pipes. This allows applications that use communication protocols to use the IIS features such as process recycling, rapid fail protection, and the common configuration system that were only available to HTTP-based applications.” * (my bold)

“The Windows Process Activation Service (WAS) manages the activation and lifetime of the worker processes that contain applications that host Windows Communication Foundation (WCF) services. 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.” ** (my bold)

WAS allows applications to be hosted in a more robust and manageable way:

  • Applications start and stop dynamically in response to incoming work items that arrive using HTTP and non-HTTP network protocols.
  • Process recycling to maintain the health of running applications.
  • Centralized application configuration and management.
  • Applications can take advantage of the IIS process model without a full IIS installation.
  • A single WAS server instance can be home to many different applications.
  • Applications are organised into groups called sites.
    • For the purposes of addressing and management.
    • Applications are also grouped together into application pools.
      • An application pool can house many different applications from many different sites.
      • Each application pool corresponds to an instance of a worker process (w3wp.exe).
  • Within a site, applications are arranged in a hierarchical manner
    • Reflects the structure of the URIs

 

* http://msdn.microsoft.com/en-us/library/ms730158.aspx
** http://msdn.microsoft.com/en-us/library/ms734677.aspx

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