How does one diagnose an HTTP 404 for a localhost service call

Question

I am working on a Windows 10 workstation invoking a localhost-hosted service. I am getting a 404.0 response. I have verified the following:

• The Physical Path directory is writable by the credentials of the associated application pool
• The application pool pipeline mode is "Classic" and start mode is "AlwaysRunning"
• I can confirm that the service does initialize on first call after iisreset.
• I have enabled failed request logging and seen those logs. They are not helpful.
• The 404 error screen says that the handler involved is svc-ISAPI-4.0_32bit
• The URL is an HTTP protocol (not SSL)
• The item under the site is configured as an application, not a virtual directory.
• "http" is the single enabled protocol at the application level and the site level
• The site is not "Default Web Site" but is mapped to 127.0.0.1
• This same application on the same workstation has worked in the past but that was a while ago
• IIS Version is 10.0.19041.1

I have tried all sorts of theories but nothing explains the 404.0. Any ideas on where to look next? Have I hit a known issue with this handler?

Answer 1

I discovered my issue. It was in the bindings definition. Since I am working on a local workstation, I am not using SSL. I neglected to change the security mode within the basicHttpBinding element in the web.config. Changing it from "Transport" to "None" did the trick.