Self-Hosting in a Managed Application
WCF services can be hosted in any managed application. This is the most flexible option because it requires the least infrastructure to deploy. You embed the code for the service inside the managed application code and then create and open an instance of the ServiceHost to make the service available.
This option enables two common scenarios: WCF services running inside console applications and rich client applications such as those based on Windows Presentation Foundation (WPF) or Windows Forms (WinForms). Hosting a WCF service inside a console application is typically useful during the application's development phase. This makes them easy to debug, easy to get trace information from to find out what is happening inside of the application, and easy to move around by copying them to new locations. This hosting option also makes it easy for rich client applications, such as WPF and WinForms applications, to communicate with the outside world. For example, a peer-to-peer collaboration client that uses WPF for its user interface and also hosts a WCF service that allows other clients to connect to it and share information.
Benefits: Flexible, Easy to deploy, Not an enterprise solution for services.
Managed Windows Services
This hosting option consists of registering the application domain (AppDomain) that hosts an WCF service as a managed Windows Service (formerly known as NT service) so that the process lifetime of the service is controlled by the service control manager (SCM) for Windows services. Like the self-hosting option, this type of hosting environment requires that some hosting code is written as part of the application. The service is implemented as both a Windows Service and as an WCF service by causing it to inherit from the ServiceBase class as well as from an WCF service contract interface. The ServiceHost is then created and opened within an overridden OnStart method and closed within an overridden OnStop method. An installer class that inherits from Installer must also be implemented to allow the program to be installed as a Windows Service by the Installutil.exe tool. The scenario enabled by the managed Windows Service hosting option is that of a long-running WCF service hosted outside of IIS in a secure environment that is not message-activated. The lifetime of the service is controlled instead by the operating system. This hosting option is available in all versions of Windows.
Benefits: Service process lifetime controlled by the operating system, not message-activated, Supported by all versions of Windows, Secure environment.
Internet Information Services (IIS)
The IIS hosting option is integrated with ASP.NET and uses the features these technologies offer, such as process recycling, idle shutdown, process health monitoring, and message-based activation. On the Windows XP and Windows Server 2003 operating systems, this is the preferred solution for hosting Web service applications that must be highly available and highly scalable. IIS also offers the integrated manageability that customers expect from an enterprise-class server product. This hosting option requires that IIS be properly configured, but it does not require that any hosting code be written as part of the application
Note that IIS-hosted services can only use the HTTP transport. Its implementation in IIS 5.1 has introduced some limitations in Windows XP. The message-based activation provided for an WCF service by IIS 5.1 on Windows XP blocks any other self-hosted WCF service on the same computer from using port 80 to communicate. WCF services can run in the same AppDomain/Application Pool/Worker Process as other applications when hosted by IIS 6.0 on Windows Server 2003. But because WCF and IIS 6.0 both use the kernel-mode HTTP stack (HTTP.sys), IIS 6.0 can share port 80 with other self-hosted WCF services running on the same machine, unlike IIS 5.1.
Benefits: Process recycling, Idle shutdown, Process health monitoring, Message-based activation, HTTP only.
Windows Process Activation Service (WAS)
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.
This hosting option requires that WAS be properly configured, but it does not require you to write any hosting code as part of the application.
Benefits: IIS is not required, Process recycling, Idle shutdown, Process health monitoring, Message-based activation, Works with HTTP, TCP, named pipes, and MSMQ.