WCF applications can be hosted in 2 main ways
- In a Windows service
- On IIS 7 and above
When WCF was first released, IIS 6 did not support hosting WCF applications that support Non-HTTP communication like Net.TCP or Net.MSMQ and developers had to rely on hosting these services on Windows Services.
With the release of IIS 7, it was possible to deploy these Non-Http based applications also on IIS 7. Following are the benefits of using IIS 7 to host WCF applications
Less development effort
Hosting on Windows service, mandates the creating of a Windows service installer project on windows service and writing code to instantiate the service, whereas the service could just be hosted on IIS by creating an application on IIS, no further development is needed, just the service implementation is needed. Hence, IIS becomes the natural option for hosting WCF services with ease. Although, you might have to create an svc file and rename your app.config to web.config if you have used the service library project template, but this could be circumvented if you either create your WCF service through the WCF application template or you could go for file less activation or you could use the publishing feature of Visual Studio to generate a svc and a web.config file.
You can monitor health of your application using AppFabric hosting if you use IIS to host your WCF application, this way you can monitor any bottlenecks in your service and adjust settings accordingly. The information ranges from the number of errors that were thrown to the number of throttled hits to the service. With AppFabric hosting you also get added benefits of configuring your endpoints behaviors and service throttling values, you can also increase your service quotes like maximum amount of bytes to be sent through the UI itself without the pain of editing configuration.. You can also get the duration it took for a call to finish and the number of calls that hit the service.
Currently there is no support for monitoring of Windows Services.
IIS takes care of process management automatically, this allows IIS to monitor worker process and automatically generate a new worker process if the current one is deadlocked or has taken more memory and shut down the one that has faulted, this counts to the great deal of reliability that IIS to offer. It also shuts down worker processes if there are no active requests for configured amount of idle time recovering system resources. Additional implementation has to be done to achieve the same thing for Windows Services.
You can also allow application pools not to recycle starting from IIS 7.5 mimicking the “always on” capabilities of Windows Services, however, this is not required for the middle layer as this is a state less service and does not require the worker process to run when there is no active requests.
Hosting you WCF applications on IIS allows applications to take advantage of IIS modules that are optional to use, for an example, you can use the request tracing module or the logging module to log request that come into IIS and the application initialization module to warm up your requests. These functionalities are not supported for Windows Services and need to be implemented separately. You can also use Connection string module to manage your connection string through the IIS Manager UI, rather than digging into the configuration files.
You can centrally manage a farm of WCF hosted in IIS in a clustered environment, this is much easier compared to clustered environment using Windows Service to host WCF application, where each service has to be managed centrally.
Sometimes you would need to make use of the ASP.NET shared model, by running the service on AspNetCompatibility mode. This can allow WCF to access session states as well as use IIS authentication mechanism.
In summary, if you have licencing issues where you cannot buy server that run on Windows 2008 or above and still runs on Windows 2003 server, then your only option of hosting Non-Http WCF services are through Windows Services other wise IIS would be the best option.