Why k8s ingress-nginx forward the reques to somewhere else?

In k8s, I deploy an app running with clusterIP(port:5270). Then I want to set up an ingress-nginx to forward the request to this app. here is the configure:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: k8s-ingress
  annotations:
    nginx.ingress.kubernetes.io/rewrite-target: /
spec:
  ingressClassName: nginx
  rules:
  - http:
      paths:
      - path: /core
        pathType: Prefix
        backend:
          service:
            name: core-service 
            port:
              number: 5270

My service is a NestJS application, and this is my request to this service :

192.168.10.131/core/api/myorder/get-order-by-id?id=1

"myorder" is one of the module I have, and I add a global prefix by using app.setGlobalPrefix('api'); in the main.ts

When enter the request path, I will get :

{"statusCode":404,"message":"ENOENT: no such file or directory, stat '/app/client/index.html'"}

It seems that the ingress can send the request to the pods, but it will look for "/app/client/index.html" which is not expected. It should access the myorder module. there is a client folder under the /app.

If I use the Nodeport to access the service instead of the ingress, everything is fine.

Here is the change I have since I got your guy’s solution:

I deployed a simple nest app, a very simple one:

It is only has a getHalleo function.
Here is the main.js:

Here is the yaml for deploying at k8s:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: k8-ingress-test1
  labels:
    app: k8-ingress-test
spec:
  replicas: 1
  selector:
    matchLabels:
      app: k8-ingress-test
  template:
    metadata:
      labels:
        app: k8-ingress-test
    spec:
      containers:
      - name: k8-ingress-test
        image: 192.168.10.145:8080/k8s-ingress-test
        imagePullPolicy: Always
        ports:
        - containerPort: 3146 
---
apiVersion: v1
kind: Service
metadata:
  name: k8-ingress-test-service
spec:
  selector:
    app: k8-ingress-test
  ports:
    - protocol: TCP
      port: 3146
      targetPort: 3146
  

Here is my new ingress-nginx:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: k8s-ingress
spec:
  ingressClassName: nginx
  rules:
  - http:
      paths:
      - path: /hello
        pathType: Prefix
        backend:
          service:
            name: k8-ingress-test-service
            port:
              number: 3146

I deleted "nginx.ingress.kubernetes.io/rewrite-target: /".
Here is my access URL:

192.168.10.131/hello

Based on my understanding, it should catch "/hello" and send "/hello" to the test app. since there is no ‘hello’ module in the app, I get the following :

{"statusCode":404,"message":"Cannot GET /hello","error":"Not Found"}

so, this is the reason why we have :

nginx.ingress.kubernetes.io/rewrite-target: /

this will edit the request from "/hello" to "/". In another word, it would send "/" to the test app instead of "/hello". so I can hit the getHello function.

For the 192.168.10.131/core/api/myorder/get-order-by-id?id=1, I can not do nginx.ingress.kubernetes.io/rewrite-target: / because it would rewrite the request to / which is wrong.

So, is there any way that I can catch the request including core, and delete the core part then send the /api/myorder/get-order-by-id?id=1 to the port 5270(and it also can catch "hello" then delete it then send "/" to the port 3146)?

Thanks