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What's The Point Of Using WCF In A Web App?
A very common approach of building web applications in .NET is to put most of the non-UI related code behind an internal WCF service layer. I used to be a fan of this approach as well, but these days I just don't see the benefit of that internal service layer anymore. The overhead that an internal WCF service layer adds to development, deployment and runtime performance just doesn't stack up favorably to the supposed benefits IMO. To be clear: I'm talking about WCF services that will only be used by the front end of your web application.
Let's talk about the overhead on development first. If you're using WCF services in your web app, you need proxies to access those services. Some people prefer to generate the proxies based on the WSDL of the services that will be used. In the worst case, this leads to regenerating proxies and all of the types that are defined in the WSDL every time you change a service contract or one of the types that are used by the services. If multiple people need to make changes to any of these concurrently, this easily leads to merging problems when people need to commit their changes. Another way is to share the same types on both sides (client & server), and implement your service proxies by inheriting from ClientBase and manually keeping the implementation of the proxies up to date with the definitions of their service contracts. This is better than regenerating a bunch of code all the time, but you're still writing a lot of redirection code for the purpose of, well, what exactly? Another possibility is to use dynamic proxies which automatically implement the service contracts but this increases the amount of infrastructure code you need to put in place and it's not always clear to everyone how exactly communication with the services happens. There's also a lot of WCF configuration for each service that you need to maintain, and it can quickly grow unwieldy.
Then there's the overhead on performance. I hope we can all agree that any operation that goes out of process is at least an order of magnitude slower than a similar operation that can be executed in process. First of all, there's the networking overhead (even if your services are hosted on the same machine as the web app) that you have to keep into account. Secondly, there is the cost of serializing and deserializing everything that is transferred between the client and the server. Even with the most efficient bindings and serializers, the cost of all of this quickly adds up on high-traffic web apps. That's not to say that WCF services are inherently slow. They can be very fast and efficient, but they'll never be as fast and efficient as executing that logic in process within the web app.
Finally, there's the extra overhead it introduces to the deployment phase:
- more endpoints to set up and transfer artifacts to
- more configuration
- more monitoring of endpoints
- more servers if you're not hosting the services and the web app on the same machine
Of course, people will argue that there a plenty of benefits to using a WCF service layer in a web app. The ones I hear about most often are the forced separation of business logic and UI logic and improved scalability and reliability. I really disagree that you need a physical separation of business and UI logic. I much prefer approaches where the separation is based on abstractions. A good example was recently posted by Ayende (here and here). And when it comes to scalability/reliability, a web app that isn't dependent on a WCF service layer is as easy (or even easier depending on your setup) to scale than one that is entirely dependent on WCF services. First of all, if you care about scalability/reliability your web app should already be prepared to run behind a load balancer. If you already have a load balancer in place, you can just add more web servers to your setup when needed. If you'd host the WCF services on the same machines that are hosting the web front end, you'd get less total throughput from one server than you would if that one server could just host a web app that fully executes in process (not including the database obviously). If you're hosting the WCF services on separate machines, you'd end up with more servers to handle the load and to achieve the reliability you need than you would with just being able to add more web servers to your setup. That also increases your licensing costs. And of course, it also means increased networking overhead on every service call, which also implies that the threads on your web servers will be blocked for longer periods while they wait for those service calls to return. Unless you're calling those services asynchronously, but most people simply don't. Also, if you have serious scalability and reliability requirements you're probably better off with asynchronous messaging solutions than with SOAP services.
WCF has its benefits (though I prefer Web API's or asynchronous messaging over SOAP services these days) and it has its use cases. I just don't think internal service layers for web apps is one of them.
What are the benefits that you think an internal WCF service layer brings to your web app? And what's your opinion on how they stack up versus the downsides?
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