Dealing with exceptions thrown in Application_Start()

https://blog.richardszalay.com/2007/03/08/dealing-with-exceptions-thrown-in-application_start/

One annoying problem I've noticed in the past is that if an exception is thrown in Application_Start() the application does not restart, resulting in subsequent requests going through to the application (aspx pages and other handlers) without the Application_Start() actions happening. This can be particularly annoying as the errors that result on the pages of the site do not tell you why Application_Start threw an exception to begin with.

Luckily there is a simple solution, and it involves using HttpRuntime.UnloadAppDomain. If you call UnloadAppDomain the application will reset and the next request will start it up again, causing Application_Start to occur again. This will allow you diagnose the error that is occuring in Application_Start and thus let you fix the problem.

Below is a sample Application_Start method:

void Application_Start(object sender, EventArgs e)
{
 try
 {
  // Some important startup stuff that must happen
 }
 catch
 {
  HttpRuntime.UnloadAppDomain(); // Make sure we try to run Application_Start again next request
  throw; // Rethrow whatever was caught
 }
}

https://docs.microsoft.com/en-us/dotnet/api/system.web.httpruntime.unloadappdomain?view=netframework-4.8

Terminates the current application. The application restarts the next time a request is received for it.

Remarks:

UnloadAppDomain is useful for servers that have a large number of applications that infrequently receive requests. Rather than keep application resources alive for the lifetime of the process, UnloadAppDomain allows programmatic shutdown of unused applications.