HTTPScaledObject with empty/omitted hosts fails to match requests with Host headers

[efernandes-dev-ops]

Report

When an HTTPScaledObject is configured without specifying hosts (either omitted entirely or set to an empty array), it fails to route HTTP requests that contain a Host header. This breaks the expected "catch-all" behavior documented in the codebase.

Expected Behavior

According to the API documentation and code comments, when spec.hosts is omitted or empty, the HTTPScaledObject should act as a catch-all and route all incoming HTTP requests regardless of their Host header value.

# HTTPScaledObject without hosts specified
apiVersion: http.keda.sh/v1alpha1
kind: HTTPScaledObject
metadata:
  name: my-app
spec:
  # hosts: []  # omitted or empty - should match ALL hosts
  scaleTargetRef:
    service: my-app
    port: 8080

Should route successfully:
✅ curl http://interceptor:8080/ (no Host header)
✅ curl -H "Host: example.com" http://interceptor:8080/ (any Host header)
✅ curl -H "Host: customer1.com" http://interceptor:8080/ (any Host header)

Actual Behavior

The current implementation only routes requests that have no Host header or an empty Host header. Any request with a populated Host header returns 404 Not Found.
Actual routing behavior:

❌ curl http://interceptor:8080/ (no Host header) → 404 Not Found
❌ curl -H "Host: example.com" http://interceptor:8080/ → 404 Not Found
❌ curl -H "Host: anything.com" http://interceptor:8080/ → 404 Not Found

Steps to Reproduce the Problem

1. Deploy KEDA HTTP Add-on (any recent version)
2. Create a test service
3. Create HTTPScaledObject without hosts
4. Test the routing

Logs from KEDA HTTP operator

example

HTTP Add-on Version

0.10.0

Kubernetes Version

1.32

Platform

Amazon Web Services

Anything else?

I have tried adding a wildcard '*' to hosts and that doesnt work

[wozniakjan]

hmm, that is a misleading comment or documentation somewhere; afaik there is no such "catch all" case implemented in the interceptor. Can you please point me to the part of the docs where this is stated? All I was able to find is this docs section
https://github.com/kedacore/http-add-on/blob/main/docs/ref/v0.10.0/http_scaled_object.md#hosts

and this API comment

http-add-on/operator/apis/http/v1alpha1/httpscaledobject_types.go

Lines 92 to 96 in 9afe55b

	// The hosts to route. All requests which the "Host" header
	// matches any .spec.hosts (and the Request Target matches any
	// .spec.pathPrefixes) will be routed to the Service and Port specified in
	// the scaleTargetRef.
	Hosts []string `json:"hosts,omitempty"`