An error occurred attempting to determine the process id of the DNX process hosting your application

Question

I get this error message when I\'m trying to start the application.

An error occurred attempting to determine the process id of the DNX process host

Answer 1

In my case in an asp net core 1.1, .net framework 4.5.2 project, the error did not refer to dnx since that is no more. Instead it referred to the project name exe. Another version of the error referred to simply being unable to connect to iis express.

The problem was the introduction of a canonical host name rewrite rule that tries to force all connections to have a host name that begins with www. e.g. redirecting gty.org to www.gty.org to conform to our ssl cert. This is fine in production but you can't force https://localhost:44347/ to begin with www and expect iis express to be able to handle it.

The solution was to comment out the rule when running in visual studio or add a condition: