OWIN & Katana



Open Web Interface for .NET (OWIN) defines an abstraction between .NET web servers and web applications. By decoupling the web server from the application, OWIN makes it easier to create middleware for .NET web development. Also, OWIN makes it easier to port web applications to other hosts—for example, self-hosting in a Windows service or other process.

OWIN is a community-owned specification, not an implementation. The Katana project is a set of open-source OWIN components developed by Microsoft. For a general overview of both OWIN and Katana, see An Overview of Project Katana. In this article, I will jump right into code to get started.

OWIN is not a framework. OWIN is a specification on how web servers and web applications should be built in order to decouple one from another and allow movement of ASP.NET applications to environments where at the current state it is not possible.

Prior to OWIN, when you are building ASP.NET application, you are inheritedly bound to IIS due to the heavy dependency on System.Web assembly.

System.Web is something that exist ever since ASP (non .NET version) and internally contains many things that you might not even need (such as Web Forms or URL Authorization), which by the default run on every request, thus consuming the resources and making ASP.NET applications in general lot slower than it’s counterparts at i.e. Node.js.

So OWIN itself does not have any tools, libraries or anything else. It is just a specification.

Katana on the other hand, is fully developed framework made to make a bridge between current ASP.NET frameworks and OWIN specification. At the moment, Katana has successfully adapted the following ASP.NET frameworks to OWIN:

  • Web API
  • Signal R

ASP.NET MVC and Web Forms are still running exclusively via System.Web, and in the long run there is a plan to decouple those as well.

On the other hand, IIS is good, resourceful host for web servers. Entire ASP.NET performance issue with using IIS has deep roots in System.Web only. Up until the recent time, when deciding how will you host your web server, you had two options:

  • IIS
  • Self-Host

So if you wanted a performance, you’d go for self-host option. If you wanted a lot of out-of-the-box features that IIS provides, you’d go for IIS but you’d lose on performance.

Now, there is a 3rd option, a Microsoft library named Helios (current codename) which intends to remove System.Web out of the way, and allow you to use IIS on more “cleaner” way, without any unnecessary libraries or modules. Helios is now in pre-release version, and is waiting for more community feedback in order to make it fully supported Microsoft product.

Hope this explanation clarifies things better for you.


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