Kubernetes Ingress non-root path 404 Not Found
Your ingress definition creates rules that proxy traffic from the {path} to the {backend.serviceName}{path}. In your case, I believe the reason it's not working is that /app is proxied to app-service:80/app but you're intending on serving traffic at the / root. Try adding this annotation to your ingress resource: nginx.ingress.kubernetes.io/rewrite-target: /
Source: https://github.com/kubernetes/ingress-nginx/tree/master/docs/examples/rewrite