This feels like not an issue with the strip-api-prefixes middleware not stripping the prefix, but some other issue with the IngressRoute configuration.

Why? Because, the 404 you are describing: "404 - page not found" sounds a lot like the Traefik default 404 page, which would mean the web traffic is not even getting to your service.

You should try the port-forward to service again (kubectl port-forward svc/api-golang -n demo-app 8000:8000) and browsing (or curling) the address with the bad prefix (http://127.0.0.1:8000/api/golang) and compare the 404 coming back from the app vs the 404 coming back from Traefik. Do they look different? If so, then the 404 with the Traefik port-forward is likely coming from Traefik due to a route issue, and not from your Go pod, because of an unstripped prefix.

There is a bunch of other things to look at that can help troubleshoot this:

• Is your Go API pod logging invalid requests, when hitting the URL with the traefik port-forward?
• Try kubectl describe on both your Middleware and IngressRoute objects to look for error messages from the controller:
  • kubectl describe ingressroute api-golang -n demo-app
  • kubectl describe middleware strip-api-prefixes -n demo-app
• If you have the Traefik dashboard enabled, look at the IngressRoute in its web UI, to see if it shows any errors, to see if it has the Middleware correctly attached to it, and that it is correctly pointing to your Service at the expected port.
• Is the Traefik controller pod(s) reporting errors related to you IngressRoute or Middleware objects?

I would be happy to help out more, but without any error messages from the live objects or the API / ingress pods, I'm just guessing, based on my own Traefik experience.