ASP.NET Core deployment to IIS error: Development environment should not be enabled in deployed applications

Question

I followed this article to deploy my ASP.NET MVC Core 1.0 app to local IIS on my Windows 10 that is using IIS 10. The application deployed successfully and it opens the home

Answer 1

I had the same problem (ASP.NET CORE 3.1) but changing "ASPNETCORE_ENVIRONMENT" did not helped.

Scouring through the web I found that in Startup.cs, Configure method, this code was hiding the real issue.

 if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

Then I deleted the If block and added Database error pages ( You might need to Install Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore from NuGet )

app.UseDatabserrorPages();

So your Startup.cs will look like this

app.UseDeveloperExceptionPage();
app.UseDatabaseErrorPage();
            
app.UseHttpsRedirection();

//Others will be Okay

Then you will see the real errors on the webpage. For me it was

Login failed for user IIS APPPOOL\DefaultAppPool

So I had to run a GRANT SCRIPT. I just had to run this script on my SQL Server

IF NOT EXISTS (SELECT name FROM sys.server_principals WHERE name = 'IIS APPPOOL\DefaultAppPool')
BEGIN
    CREATE LOGIN [IIS APPPOOL\DefaultAppPool] 
      FROM WINDOWS WITH DEFAULT_DATABASE=[master], 
      DEFAULT_LANGUAGE=[us_english]
END
GO
CREATE USER [WebDatabaseUser] 
  FOR LOGIN [IIS APPPOOL\DefaultAppPool]
GO
EXEC sp_addrolemember 'db_owner', 'WebDatabaseUser'
GO

You can see this link : https://docs.microsoft.com/en-us/aspnet/web-forms/overview/deployment/visual-studio-web-deployment/deploying-to-iis

And my problem was solved. Hope this helps somebody.