I am using DNS based service discovery to discover services in K8s cluster. From this link it is very clear that to discover a service named my-service we can do name lookup "my-service.my-ns" and the pod should be able to find the services.

However in case of port discovery for the service the solution is to use is "_http._tcp.my-service.my-ns" where

_http refers to the port named http in my-service.

But even after using _http._tcp.my-service it doesn't resolve port number. Below are the details.

my-service which needs to be discovered

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    app: my-service
  ports:
    - name: http
      protocol: TCP
      port: 5000
      targetPort: 5000

client-service yaml snippet trying to discover my-service and its port.

spec:
  containers:
  - name: client-service
    image: client-service
    imagePullPolicy: Always
    ports:
      - containerPort: 7799
    resources:
      limits:
        cpu: "100m"
        memory: "500Mi"
    env:
    - name: HOST
      value: my-service
    - name: PORT
      value: _http._tcp.my-service

Now when I make a request it fails and logs following request which is clearly incorrect as it doesn't discover port number.

 http://my-service:_http._tcp.my-service

I am not sure what wrong I am doing here, but I am following the same instructions mentioned in document.

Can somebody suggest what is wrong here and how we can discover port using DNS based service discovery? Is my understanding wrong here that it will return the literal value of port?

Cluster details

K8s cluster version is 1.11.5-gke.5 and Kube-dns is running

Additional details trying to discover service from busybox and its not able to discover port value 5000

kubectl exec  busybox -- nslookup my-service
Server:         10.51.240.10
Address:        10.51.240.10:53

Name:   my-service.default.svc.cluster.local
Address: 10.51.253.236

*** Can't find my-service.svc.cluster.local: No answer
*** Can't find my-service.cluster.local: No answer
*** Can't find my-service.us-east4-a.c.gdic-infinity-dev.internal: No answer
*** Can't find my-service.c.gdic-infinity-dev.internal: No answer
*** Can't find my-service.google.internal: No answer
*** Can't find my-service.default.svc.cluster.local: No answer
*** Can't find my-service.svc.cluster.local: No answer
*** Can't find my-service.cluster.local: No answer
*** Can't find my-service.us-east4-a.c.gdic-infinity-dev.internal: No answer
*** Can't find my-service.c.gdic-infinity-dev.internal: No answer
*** Can't find my-service.google.internal: No answer


kubectl exec  busybox -- nslookup _http._tcp.my-service
Server:         10.51.240.10
Address:        10.51.240.10:53

** server can't find _http._tcp.my-service: NXDOMAIN

*** Can't find _http._tcp.my-service: No answer