title: "Host ASP.NET Web API 2 in an Azure Worker Role | Microsoft Docs"
author: MikeWasson
description: "This tutorial shows how to host ASP.NET Web API in an Azure Worker Role, using OWIN to self-host the Web API framework. Open Web Interface for .NET (OWIN) de..."
> This tutorial shows how to host ASP.NET Web API in an Azure Worker Role, using OWIN to self-host the Web API framework.
>
> [Open Web Interface for .NET](http://owin.org/) (OWIN) defines an abstraction between .NET web servers and web applications. OWIN decouples the web application from the server, which makes OWIN ideal for self-hosting a web application in your own process, outside of IIS–for example, inside an Azure worker role.
>
> In this tutorial, you'll use the Microsoft.Owin.Host.HttpListener package, which provides an HTTP server that be used to self-host OWIN applications.
>
> ## Software versions used in the tutorial
>
>
> - [Visual Studio 2013](https://www.microsoft.com/visualstudio/eng/2013-downloads)
> - Web API 2
> - [Azure SDK for .NET 2.3](https://azure.microsoft.com/en-us/downloads/)
## Create a Microsoft Azure Project
Start Visual Studio with administrator privileges. Administrator privileges are needed to debug the application locally, using the Azure compute emulator.
On the **File** menu, click **New**, then click **Project**. From **Installed Templates**, under Visual C#, click **Cloud** and then click **Windows Azure Cloud Service**. Name the project "AzureApp" and click **OK**.
In the **New Windows Azure Cloud Service** dialog, double-click **Worker Role**. Leave the default name ("WorkerRole1"). This step adds a worker role to the solution. Click **OK**.
Click **Endpoints**, and then click **Add Endpoint**.
In the **Protocol** dropdown list, select "http". In **Public Port** and **Private Port**, type 80. These port numbers can be different. The public port is what clients use when they send a request to the role.
Next, add a Web API controller class. Right-click the WorkerRole1 project and select **Add** / **Class**. Name the class TestController. Replace all of the boilerplate code in this file with the following:
The **WebApp.Start** method starts the OWIN host. The name of the `Startup` class is a type parameter to the method. By convention, the host will call the `Configure` method of this class.
Override the `OnStop` to dispose of the *\_app* instance:
Build the solution, and press F5 to run the application locally in the Azure Compute Emulator. Depending on your firewall settings, you might need to allow the emulator through your firewall.
> [!NOTE]
> If you get an exception like the following, please see [this blog post](https://blogs.msdn.com/b/praburaj/archive/2013/11/20/fileloadexception-on-microsoft-owin-when-running-on-worker-role.aspx) for a workaround. "Could not load file or assembly 'Microsoft.Owin, Version=2.0.2.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)"
The compute emulator assigns a local IP address to the endpoint. You can find the IP address by viewing the Compute Emulator UI. Right-click the emulator icon in the task bar notification area, and select **Show Compute Emulator UI**.
Find the IP address under Service Deployments, deployment [id], Service Details. Open a web browser and navigate to http://*address*/test/1, where *address* is the IP address assigned by the compute emulator; for example, `http://127.0.0.1:80/test/1`. You should see the response from the Web API controller:
For this step, you must have an Azure account. If you don't already have one, you can create a free trial account in just a couple of minutes. For details, see [Microsoft Azure Free Trial](https://azure.microsoft.com/en-us/pricing/free-trial/?WT.mc_id=A261C142F).
In Solution Explorer, right-click the AzureApp project. Select **Publish**.
