Ingress - simple fanout configuration not working - kubernetes

Question

I'm using Ubuntu 20.04.2 LTS. I installed microk8s 1.20.6 rev 2143 and experimenting with ingress. I must be missing something - but it doesn't work as I expect it to. I tracked the strange behavior down to the following configuration:
ingress.yaml:
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: my-ubuntu
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /
spec:
rules:
- host: my-ubuntu
http:
paths:
- path: /
pathType: Prefix
backend:
service:
name: nginx
port:
number: 80
- path: /nginx
pathType: Prefix
backend:
service:
name: nginx
port:
number: 80
nginx-service.yaml:
apiVersion: v1
kind: Service
metadata:
name: nginx
spec:
ports:
- port: 80
name: http
- port: 443
name: https
type: ClusterIP
selector:
app: nginx
Now,
curl my-ubuntu/ # this returns Welcome page, as expected
curl my-ubuntu/nginx # this returns Welcome page, as expected
curl my-ubuntu/bad-page.html # this returns 404 Not Found, as expected
curl my-ubuntu/nginx/bad-page.html # this returns Welcome page. WHY?
Any request under my-ubuntu/nginx/* returns Welcome page, even when the url is correct and should have returned different content. Did I configure something wrong?
I was able to reproduce the same strange behavior using Docker for Windows + WSL2 + Ubuntu + ingress installed using:
kubectl apply -f https://raw.githubusercontent.com/kubernetes/ingress-nginx/controller-v0.41.2/deploy/static/provider/cloud/deploy.yaml
EDIT
nginx-deployment.yaml I used:
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx
labels:
app: nginx
spec:
replicas: 1
revisionHistoryLimit: 0
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: nginx
imagePullPolicy: Always
name: nginx
When I try /nginx/ instead of /nginx like #HarshManvar suggested, I get this behavior:
curl my-ubuntu/ # this returns Welcome page, as expected
curl my-ubuntu/bad-page.html # this returns 404 Not Found, as expected
curl my-ubuntu/nginx # this returns 404 Not Found
curl my-ubuntu/nginx/ # this returns Welcome page
curl my-ubuntu/nginx/bad-page.html # this returns Welcome page
Kubernetes Ingress documentation about Simple fanout also does use /nginx pattern but not working as described above.

Answer 1

https://kubernetes.github.io/ingress-nginx/examples/rewrite/ explains how to use rewrite-target annotation. I was able to make it work with the following ingress.yaml:
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
name: my-ubuntu
annotations:
nginx.ingress.kubernetes.io/rewrite-target: /$1
spec:
rules:
- host: localhost
http:
paths:
- path: /(.*)
pathType: Prefix
backend:
service:
name: nginx
port:
number: 80
- path: /nginx($|/.*)
pathType: Prefix
backend:
service:
name: nginx
port:
number: 80
Each path defines regular expression with ( ), which yields $1, $2, etc., aka. regex capture group variables. Now you put rewrite-target using those variables, and that will be the actual URL that is passed to the service's container that handles the request.
Maybe there is another way, but this is the only way I was able to make it work.