Windows Communication Foundation on IIS Deployment

At work we’ve been putting together a new schedule proofing experience for our campus (and possibly the rest of the University system) which would allow the schedule proofers to do all their work via a web-based interface. As we’re a primarily Microsoft-based house, the entire system is being built upon newer Microsoft platforms, for better or worse (usually the latter). We’ve been building the system using Silverlight 2.0 for the front end, Windows Workflow for the middle-layer, and Windows Communication Foundation for the communication between the two.

WCF is an interesting technology, because it makes producing web-based or application-based services pretty simple, and the framework modifies it’s behaviour based on how you deploy it. Need XML-based output? It’ll do that. Binary output more your style, feel free. If you want it, WCF can do JSON as well. The technology is handy, because it makes it so that you can focus on the implementation details of your web service, rather than worrying about the intricacies of SOAP or JSON data-exchange. The technology is compelling enough that the Mono project founded Olive to bring WCF to Mono.

The technology has a lot of really cool potential, but it suffers from some inherent design flaws that are hideously unfortunate. First, it seems frighteningly difficult to put more than one WCF web-service in an IIS instance. This has had all sorts of implication for people doing ASP.NET in Shared Web Host environments. Requiring unnecessary complexity to work around a bad behavior. While our problem is a little different, and I’ll get into it in a moment, I’m a bit confused as to why how the solution linked above, which is to define a Custom ServiceHostFactory object, even works, since the Factory attribute doesn’t seem valid, at least according to my VS 2008 instance. I’m not going to pursue that direction, however, as our issue stems from a slightly different, but I would argue far more common position.

We currently have three web-services designed. All three have their own SVC files in our web-project, and all three are properly defined WCF services. They all work properly on the local test server, and they were created as each their own services, because they each deal with different sets of data. Two are used to query into certain data systems, and in the interests of proper code separation, as well as the potential for reuse, we wanted to keep them separately. Even the old ASP.NET Web Services would have allowed this. Not WCF, though.

WCF_Error.png

That’s right, try to host more than one WCF service in a single IIS application, and an exception is thrown. Great work, Microsoft. I probably wouldn’t be so annoyed if Microsoft wasn’t trying to defend their position on this.

Wenlong Dong posted in the above thread link: Unfortunately the behavior is by design. WCF does not support multiple IIS bindings for the same protocol (here it is HTTP) for the same web site. This is for simplicity, especially it did not seem to be an important scenario. Is this a very important scenario for you? Can’t you host different services in different web sites (with different ports of course)? If this does block you, we may think about revisiting this issue again.

SIMPLICITY?!? DIFFERENT WEB SITES?!? WITH DIFFERENT PORTS?!?

You have got to be fucking kidding me.

Damn it Microsoft, as far as I can tell, if I’m hosting in IIS, I have to reference the service by it’s full URL anyway (typically ending in .svc), so the Service already has a uniquely identifying endpoint. That’s really all you should care about, that some sort of a URL can identify the location of the service. If I want to host them all on the same port, but with different URLs, why on earth should that matter to your framework? The URL is already telling you which code to run, how can you possibly have any confusion over this?

Luckily, Dan Meineck, a .NET Web Developer from the UK, has come up with a solution. Is his workaround complicated? Yes. Is it unreasonable? Yes. Does it work? Apparently.

The solution boils down to this: 1. Using .NET’s partial classes, put all your webservices in one class, but each discrete bit in different files, each file should only indicate the WCF interface which that file defines. 2. Modify your Web.Config (or App.Config) file, and in the sytem.serviceModel section, for the service, define endpoint blocks for each of your services, you can specify the specific contract Interface on each endpoint, so that only the methods you want are available on that endpoint.

Ultimately, this provides the exact behavior we want, but it’s really not very clean, and forcing users into this particular model is confusing and pointless. I understand Microsoft feels that the interface specifies the behavior, and is therefore the important part of the definition, but this decision will make it far more difficult for me to integrate a web service from one project into a second project, and frankly if this was simpler for anyone (even Microsoft from an implementation standpoint) it suggests to me that there are deeper design issues in the way that WCF works.

I’m refactoring the code today, to match Mr. Meineck’s suggestions, but it just seems so unnecessary, and pointless. Please fix this, Microsoft.