A kubectl debugging workflow

Narrow it down in a fixed order

Work outside in: is the pod running, is it ready, does the service have endpoints, does the ingress route to it. Each step eliminates a layer, which beats guessing.

Port-forwarding straight to a pod bypasses the service and ingress entirely. If the application answers there, your problem is in the routing layers, not the code.

Minimal images with no shell are exactly the case ephemeral debug containers exist for: attach a container with tools into the running pod namespace without rebuilding the image.