Why is my error not being caught by Application_Error() on Azure?

14 November 2014

Are you having errors that are triggering Global.asax.cs.Application_Error() locally correctly but don't work when you deploy to Azure or another remote IIS host?

Check if the value of CustomErrors in your web.config is 'On' or 'RemoteOnly' (or missing - which defaults to 'RemoteOnly'). 'RemoteOnly' means that the full error message is hidden from the user on remote sites, like Azure, but will be shown when running on your local machine.So when an error occurs on Azure MVC doesn't go to Global.asax.cs to call the Application_Error method, it instead redirects to the first Error view page it can find and discards the error.

Solution

The solution is just to add a custom filter to log the error in addition to showing the page.

Make this class:

using log4net;
using StructureMap;
using System;
using System.Web;
using System.Web.Mvc;

public class ErrorHandlingFilter : IExceptionFilter
{

    public void OnException(ExceptionContext context)
    {
        try
        {
            var exception = context.Exception;
            if (!(exception is HttpException)) //ignore "file not found"
                ObjectFactory.GetInstance<ILog>().Error("An unhandled exception was caught in ErrorHandlingFilter.OnException()", exception);
        }
        finally
        {
            context.Result = new RedirectToRouteResult(new RouteValueDictionary(new { controller = "Shared", action = "Error" }));
            context.Result.ExecuteResult(context.Controller.ControllerContext);
        }
    }
}

Then add it to your startup FilterConfig.cs:

public class FilterConfig
{
    public static void RegisterGlobalFilters(GlobalFilterCollection filters)
    {
        filters.Add(new ErrorHandlingFilter()); //must be before HandleErrorAttribute
        filters.Add(new HandleErrorAttribute());
    }
}

For more info see: http://stackoverflow.com/questions/6508415/application-error-not-firing-when-customerrors-on#answer-7551256

Richard JE Cooke

Why is my error not being caught by Application_Error() on Azure?

Solution