How to get the DNS name of a service in google cloud platform?

Question

In this repository https://github.com/mappedinn/kubernetes-nfs-volume-on-gke I am trying to share a volume through NFS service on GKE. The NFS file sharing is successful if hard coded IP address is used.

But, in my point of view, it would be better to use DNS name in stead of hard coded IP address.

Below is the declaration of the NFS service being used for sharing a volume in Google Cloud Platform:

apiVersion: v1
kind: Service
metadata:
  name: nfs-server
spec:
  ports:
    - name: nfs
      port: 2049
    - name: mountd
      port: 20048
    - name: rpcbind
      port: 111
  selector:
    role: nfs-server

Below is the definition of the PersistentVolume with hard coded IP address:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: wp01-pv-data
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteMany
  nfs:
    server: 10.247.248.43 # with hard coded IP, it works
    path: "/"

Below is the definition of the PersistentVolume with DNS name:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: wp01-pv-data
spec:
  capacity:
    storage: 5Gi
  accessModes:
    - ReadWriteMany
  nfs:
    server:  nfs-service.default.svc.cluster.local # with DNS, it does not works
    path: "/"

I am using this https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/ for getting the DNS of the service. Is there any thing missed?

Thanks

Answer 1

The problem is in DNS resolution on node it self. Mounting of the NFS share to the pod is a job of kubelet that is launched on the node. Hence the DNS resolution happens according to /etc/resolv.conf on the node it self as well. What could suffice is adding a nameserver <your_kubedns_service_ip> to the nodes /etc/resolv.conf , but it can become somewhat chicken-and-egg problem in some corner cases

Answer 2

I solved the problem by just upgrading kubectl of my GKE cluster from the version 1.7.11-gke.1 to 1.8.6-gke.0 .

kubectl version
# Client Version: version.Info{Major:"1", Minor:"8", GitVersion:"v1.8.6", GitCommit:"6260bb08c46c31eea6cb538b34a9ceb3e406689c", GitTreeState:"clean", BuildDate:"2017-12-21T06:34:11Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"linux/amd64"}
# Server Version: version.Info{Major:"1", Minor:"8+", GitVersion:"v1.8.6-gke.0", GitCommit:"ee9a97661f14ee0b1ca31d6edd30480c89347c79", GitTreeState:"clean", BuildDate:"2018-01-05T03:36:42Z", GoVersion:"go1.8.3b4", Compiler:"gc", Platform:"linux/amd64"}

Actually, this the final version of yaml files:

apiVersion: v1
kind: Service
metadata:
  name: nfs-server
spec:
  # clusterIP: 10.3.240.20
  ports:
    - name: nfs
      port: 2049
    - name: mountd
      port: 20048
    - name: rpcbind
      port: 111
  selector:
    role: nfs-server
#  type: "LoadBalancer"

and

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs
spec:
  capacity:
    storage: 1Mi
  accessModes:
    - ReadWriteMany
  nfs:
    # FIXED: Use internal DNS name
    server: nfs-server.default.svc.cluster.local 
    path: "/"