.net - All requests to ASP.NET Web API return 404 error

Question

I have an ASP.NET MVC 4 web site that includes Web API. The site is developed and tested with Visual Studio 2012 and .NET 4.5 on Windows 8 with IIS Express as web server. In this development environment everything works.

Now it is deployed on a Windows 2008 R2 (SP1) Server with IIS 7.5. .NET 4.0 and 4.5 are installed. The application pool is running with .NET 4.0 in integrated pipeline mode.

In this production environment the MVC web site works, Web API does not. For every request, no matter if GET or POST I get a 404 error. If I just enter a Web API Url in the browser (IE 9 opened locally on the server) to run a GET request I get a 404 page. If I issue a POST request from a Web API client application I get a 404 as well and the message:

No HTTP resource was found that matches the request URI

I've created a test website with MVC 4 and Web API as well and deployed it on the same server and the Web API works. Web API and MVC assemblies have the same version number in both projects.

Furthermore I have added the Web API Route Debugger to the application. If I use a valid route like http://myserver/api/order/12 I get the following result:

For me this means that the correct route template Api/{Controller}/{Id} has been found and correctly parsed into a controller Order and Id=12. The controller (derived from ApiController) exists in the web assembly where also all MVC controllers are.

However, I don't know what the status 000 could mean and why there is no "Route selecting" section displayed (which is normally the case even if the assembly doesn't contain a single ApiController, see screenshots on the linked page above). Somehow it looks like no ApiController is found or even not searched for or the search fails silently.

The IIS log files don't show anything useful. Changing various application pool settings and using the same app pool for the test and the real application didn't help.

I am currently in the process to remove "features", configuration settings, third party assemblies, etc. from the application to bring it down to the small size of the test application in the end and hoping that at some point it starts to work.

Does somebody have a clue what the issue could be? Also any debugging or logging idea to possibly find the reason is very welcome.

Edit

Thanks to Darrel Miller's tip in the comments below I have integrated Tracing for ASP.NET Web Api.

For the (GET) request URL http://myserver/api/order/12 I get the following:

• In development environment, successful (in short form):

Message: http://localhost:50020/api/order/12; Category: System.Web.Http.Request

Controller selection and instantiation...

Operator: DefaultHttpControllerSelector; Operation: SelectController; Message: Route="controller:order,id:12"; Category: System.Web.Http.Controllers

Operator: DefaultHttpControllerSelector; Operation: SelectController; Message: Order; Category: System.Web.Http.Controllers

Operator: HttpControllerDescriptor; Operation: CreateController; Message: ; Category: System.Web.Http.Controllers

Operator: DefaultHttpControllerActivator; Operation: Create; Message: ; Category: System.Web.Http.Controllers

Operator: DefaultHttpControllerActivator; Operation: Create; Message: MyApplication.ApiControllers.OrderController; Category: System.Web.Http.Controllers

Action selection, parameter binding and action invocation follows...

Content negotiation and formatting for result...

Operator: DefaultContentNegotiator; Operation: Negotiate; Message: Typ = "String" ... more

Disposing the controller...

Operator: OrderController; Operation: Dispose; Message: ; Category: System.Web.Http.Controllers

• In production environment, not successful (in short form):

Message: http://myserver/api/order/12; Category: System.Web.Http.Request

Operator: DefaultHttpControllerSelector; Operation: SelectController; Message: Route="controller:order,id:12"; Category: System.Web.Http.Controllers

The whole part of controller activation, action selection, parameter binding, action invocation is missing and it follows content negotiation and formatting for the error message immediately:

Operator: DefaultContentNegotiator; Operation: Negotiate; Message: Type = "HttpError" ... more

Answer 1

Thanks to Kiran Challa's comment and source code from this answer I was able to figure out that an assembly (the ReportViewer 11 assembly for SQL Server Reporting Services) was missing on the production server.

Although no ApiController is in this assembly it seems to cause that controllers in assemblies - in this case my Web project's assembly - that are referencing the missing assembly are not found.

Apparently this behaviour is related to this piece of code from the Web API's DefaultHttpControllerTypeResolver source:

List<Type> result = new List<Type>();

// Go through all assemblies referenced by the application
// and search for types matching a predicate
ICollection<Assembly> assemblies = assembliesResolver.GetAssemblies();
foreach (Assembly assembly in assemblies)
{
    Type[] exportedTypes = null;
    if (assembly == null || assembly.IsDynamic)
    {
        // can't call GetExportedTypes on a dynamic assembly
        continue;
    }

    try
    {
        exportedTypes = assembly.GetExportedTypes();
    }
    catch (ReflectionTypeLoadException ex)
    {
        exportedTypes = ex.Types;
    }
    catch
    {
        // We deliberately ignore all exceptions when building the cache. If 
        // a controller type is not found then we will respond later with a 404.
        // However, until then we don't know whether an exception at all will
        // have an impact on finding a controller.
        continue;
    }

    if (exportedTypes != null)
    {
        result.AddRange(exportedTypes.Where(x => IsControllerTypePredicate(x)));
    }
}

I don't know if it has to be this way and I am not quite convinced by the comment in the code but this catch ... continue block is rather silent about a possible problem and it took me a huge amount of time and frustration to find it. I even knew that the ReportViewer wasn't installed yet. I tried to install it and dependent assemblies but it was blocked by another running process on the server, so I decided to postpone the installation until I could contact the administrator and focus on MVC and WebAPI testing first - big mistake! Without Kiran's debugging code snippet I had never had the idea that the existence of a ReportViewer.dll could have anything to do with controller type resolution.

In my opinion there is room for improvement for the average developer like me who doesn't have a deeper knowledge about the inner workings of Web API.

After installing the missing ReportViewer.dll the problem disappeared.

Here are questions about the same symptom which might have the same reason:

• All ASP.NET Web API controllers return 404
• .Net Web API No HTTP resource was found that matches the request URI
• http://forums.asp.net/t/1861082.aspx/1?All+controllers+break+404+whenever+I+publish+to+Azure

Edit

I have issued a request for improvement on CodePlex:

http://aspnetwebstack.codeplex.com/workitem/1075

Edit 2 (Aug 11 '13)

The issue has been fixed for WebAPI v5.0 RC. See the link above to the workitem and its comments section for details.