.Net core app runs with EXE but does not run on IIS - amazon-web-services

Question

I have a .Net Core 6 app which runs fine locally, it also runs fine when I manually start the exe in the publish folder.
However when I run on IIS, it gives the following error.
The server is an AWS EC2 server, I have all ports open as a test as incoming on the firewall, I have also tried to disable the firewall completely and also allowing the app through the firewall. As far as I'm aware there is no AV on the EC2 instance.
I have added the .net core 6 runtime and I have also installed the .NET Core hosting bundle found here:
https://dotnet.microsoft.com/en-us/download/dotnet/6.0
When I have checked the event viewer logs I get this error message:
Application: WebApi.exe
CoreCLR Version: 6.0.222.6406
.NET Version: 6.0.2
Description: The process was terminated due to an unhandled exception.
Exception Info: System.IO.IOException: Failed to bind to address http://localhost:4000.
System.AggregateException: One or more errors occurred. (An attempt was made to access a socket in a way forbidden by its access permissions.) (An attempt was made to access a socket in a way forbidden by its access permissions.)
System.Net.Sockets.SocketException (10013): An attempt was made to access a socket in a way forbidden by its access permissions.
at System.Net.Sockets.Socket.UpdateStatusAfterSocketErrorAndThrowException (SocketError error, String callerName)
at System.Net.Sockets.Socket.DoBind(EndPoint endPointSnapshot, SocketAddress socketAddress)
at System.Net.Sockets.Socket.Bind(EndPoint localEP)
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportOptions.CreateDefaultBoundListenSocket(EndPoint endpoint)
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketConnectionListener.Bind()
at Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets.SocketTransportFactory.BindAsync(EndPoint endpoint, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Infrastructure.TransportManager.BindAsync(EndPoint endPoint, ConnectionDelegate connectionDelegate, EndpointConfig endpointConfig, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl.<>c__DisplayClass30_0`1.<g__OnBind|0>d.MoveNext()
--- End of stack trace from previous location ---
at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.AddressBinder.BindEndpointAsync(ListenOptions endpoint, AddressBindContext context, CancellationToken cancellationToken)
at Microsoft.AspNetCore.Server.Kestrel.Core.LocalhostListenOptions.BindAsync(AddressBindContext context, CancellationToken cancellationToken)
--- End of inner exception stack trace ---
I have read there is a setting on old versions of .NetCore to specify the use of IIS, but I can't see one for .Net Core 6.
I am pulling my hair out trying to figure out what is wrong.
Here is what is shown when I run the exe on it's own, which is correct.

Answer 1

I have finally found the reason.
It was due to my program.cs file having this line at the bottom:
app.Run("http://localhost:4000");
I changed this to the following and changed the port to 5000 on IIS and it all started working
app.Run();