ASP.NET Core Troubleshooting

So, your ASP.NET Core application doesn't log errors to elmah.io? Here is a list of things to try out:

• Run the diagnose command with the elmah.io CLI as shown here: Diagnose potential problems with an elmah.io installation.
• Make sure to reference the most recent version of the Elmah.Io.AspNetCore NuGet package.
• Make sure that the Elmah.Io.Client NuGet package is installed and that the major version matches that of Elmah.Io.AspNetCore.
• Make sure that you are calling both the AddElmahIo- and UseElmahIo-methods in the Program.cs file (or Startup.cs for older applications), as described on Logging to elmah.io from ASP.NET Core.
• Make sure that you call the UseElmahIo-method after invoking other Use* methods that in any way inspect exceptions (like UseDeveloperExceptionPage and UseExceptionHandler).
• Make sure that you call the UseElmahIo-method before invoking UseMvc, UseEndpoints, and similar.
• Make sure that your server has an outgoing internet connection and that it can communicate with api.elmah.io on port 443. The integration for ASP.NET Core support setting up an HTTP proxy if your server doesn't allow outgoing traffic. Check out Logging through a proxy for details.
• Make sure that you didn't enable any Ignore filters or set up any Rules with an ignore action on the log in question.
• Make sure that you don't have any code catching all exceptions happening in your system and ignoring them (could be a logging filter, a piece of middleware, or similar).
• Make sure that you haven't reached the message limit included in your current plan. Your current usage can be viewed on the Subscription tab on organization settings.

Common problems and how to fix them

Here you will a list of common exceptions and how to solve them.

InvalidOperationException

Exception

[InvalidOperationException: Unable to resolve service for type 'Elmah.Io.AspNetCore.IBackgroundTaskQueue' while attempting to activate 'Elmah.Io.AspNetCore.ElmahIoMiddleware'.]
   Microsoft.Extensions.Internal.ActivatorUtilities+ConstructorMatcher.CreateInstance(IServiceProvider provider)
   Microsoft.AspNetCore.Builder.UseMiddlewareExtensions+<>c__DisplayClass4_0.<UseMiddleware>b__0(RequestDelegate next)
   Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder.Build()
   Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

Solution

You forgot to call the AddElmahIo-method in the Program.cs file:

builder.Services.AddElmahIo(o =>
{
    // ...
});

ArgumentException

Exception

[ArgumentException: Input an API key Parameter name: apiKey]
   Elmah.Io.AspNetCore.Extensions.StringExtensions.AssertApiKey(string apiKey)
   Elmah.Io.AspNetCore.ElmahIoMiddleware..ctor(RequestDelegate next, IBackgroundTaskQueue queue, IOptions<ElmahIoOptions> options)
   Microsoft.Extensions.Internal.ActivatorUtilities+ConstructorMatcher.CreateInstance(IServiceProvider provider)
   Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)
   Microsoft.AspNetCore.Builder.UseMiddlewareExtensions+<>c__DisplayClass4_0.<UseMiddleware>b__0(RequestDelegate next)
   Microsoft.AspNetCore.Builder.Internal.ApplicationBuilder.Build()
   Microsoft.AspNetCore.Hosting.Internal.WebHost.BuildApplication()

Solution

You forgot to call the AddElmahIo-method in the Program.cs file:

builder.Services.AddElmahIo(o =>
{
    // ...
});

or you called AddElmahIo without options and didn't provide these options elsewhere:

builder.Services.AddElmahIo();

Even though you configure elmah.io through appsettings.json you still need to call AddElmahIo. In this case, you can register ElmahIoOptions manually and use the empty AddElmahIo overload:

builder.Services.Configure<ElmahIoOptions>(Configuration.GetSection("ElmahIo"));
builder.Services.AddElmahIo();

An error occurred while starting the application

If you see the error An error occurred while starting the application and the exception isn't logged to elmah.io, the error probably happens before hitting the elmah.io middleware. To help find out what is going on, add the following lines to your Program.cs file:

builder.WebHost.UseSetting(WebHostDefaults.DetailedErrorsKey, "true");
builder.WebHost.CaptureStartupErrors(true);

URL missing when using Map

When handling requests with the Map method, ASP.NET Core will remove the path from HttpRequest.Path. In this case, Elmah.Io.AspNetCore will look for an URL in the HttpRequest.PathBase property. This is not already enough and won't always return the right URL. Consider using the MapWhen method instead.

Thread pool thread or asynchronous tasks blocked on a synchronous call

Azure and other systems with runtime diagnostics and validation may complain with the error Thread pool thread or asynchronous tasks blocked on a synchronous call in the Elmah.Io.AspNetCore package. This can be caused by our implementation of the package using a background worker for processing batches of messages. This background worker runs in a single thread and will never cause thread starvation as suggested by the error. We may want to move the internal implementation from BlockingCollection to Channel at some point.

This article was brought to you by the elmah.io team. elmah.io is the best error management system for .NET web applications. We monitor your website, alert you when errors start happening, and help you fix errors fast.

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