ASP.NET Core 1.1 runs fine locally but when publishing to Azure says “An error occurred while starting the application.”

Question

I\'ve been developing an ASP.NET Core web app, based largely on the MVC template provided in Visual Studio 2017 RC2. It runs just fine in local debug mode, but when I try to

Answer 1

Question is probably duplicated - please refer to ASP.NET Core hosting - 500 internal server error.

Quick answer:

You need to set: stdoutLogEnabled="true" and stdoutLogFile=".\logs\stdout". Also, you need to create logs folder manually.

Answer 2

In my case, it was because I was trying to publish user secrets for use with Fabook OAuth. I know that's a very situational specific answer, but OAuth seems pretty common these day. User Secrets, it turns out, are not meant to be published. Who knew.

So to test this I temporarily changed the following code in startup.cs. This data should be not hard coded as a part of best practice, as it would end up in clear text in source control.

Before

    app.UseFacebookAuthentication(new FacebookOptions()
    {
        AppId = Configuration["Authentication:Facebook:AppId"],
        AppSecret = Configuration["Authentication:Facebook:AppSecret"]
    });

After

    app.UseFacebookAuthentication(new FacebookOptions()
    {
        AppId = "0000000000000", // your value
        AppSecret = "0000000000000000000000000000000" // your value
    });

Then it worked.

Answer 3

In My case, that was because I was trying to get a some data in Startup, and dbcontext was not updated in production environment.

Changed my ConnectionString to Production and runned Update-Database, and problem solved.

Answer 4

Since many different problems can cause this error page, I can strongly recommend the following in order to determine the root cause quickly and easily, without wrestling Azure (or any server/platform for that matter) to get logs.

You can enable extremely helpful developer friendly error messages at startup by setting the .UseSetting("detailedErrors", "true") and .CaptureStartupErrors(true) actions in your Program.cs file.

For ASP.NET Core 1.x

public static void Main(string[] args)
{
  var host = new WebHostBuilder()
      .UseKestrel()
      .UseContentRoot(Directory.GetCurrentDirectory())
      .UseSetting("detailedErrors", "true")
      .UseIISIntegration()
      .UseStartup<Startup>()
      .CaptureStartupErrors(true)
      .Build();

  host.Run();
}

(2018/07) Update for ASP.NET Core 2.1

public class Program  
{
    public static void Main(string[] args)
    {
        BuildWebHost(args).Run();
    }

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .CaptureStartupErrors(true)
            .UseSetting("detailedErrors", "true")
            .UseStartup<Startup>()
            .Build();
}

• These settings should be removed as soon as your troubleshooting is complete so as not to expose your application to malicious attacks.

Answer 5

Thanks everyone for your suggestions. The only thing that worked in the end though is deleting that Azure web app that I couldn't publish to, and creating a brand new one. I guess maybe some of the .dlls from the previous runtime environment were still hanging around or not being updated... Whatever it was, re-creating it worked. Hopefully I don't get this error again though, because you can't really do this kind of stuff in production.

Making changes to the global.json file seemed to have no effect.

Creating an entirely new API from a template didn't help either, the issue was with the Azure Web App itself, as everything was running fine locally.

Another very helpful tip was to add logging (and the "logs" file in the root) as per the other answer. That at least pointed me in the right direction. Also checking your runtime with dotnet --version.

Again thanks for everyone's help!

Answer 6

DELETE all existing dll from wwwroot/your_application_folder, then copy all of the publish output files&folders.

The problem occurs when the NUGETS update it self. If you don't clean the existing files under wwwroot/your_application_folder IIS gives the error above.