I was able to reproduce this locally with the following setup:
- Use NetSh.exe or similar tool to reserve
http://localhost:8080/
- Call
WebApp.Start<Startup>("http://*:8080")
- Browse to
http://localhost:8080/
What happens is that Http.Sys accepts the incoming request, examines the host header, decides that there is a reservation for localhost:8080, but realizes that no application is listening to localhost:8080, only *:8080. Http.Sys then returns the 503.
Solutions:
- Try
WebApp.Start<Startup>("http://+:8080")
- Remove the Http.Sys/NetSh registration