It's how kubernetes service nodeport works. NodePort service bind on random port in the range 30000-32767. If you want to specify the bind port add nodePort attribute to set it (docs ) but it must be in the required range. For the example I choose 30007 :

apiVersion: v1
kind: Service
metadata:
  name: frontend
  labels:
    app: {{ .Release.Name }}
    product: {{ .Values.product }}
    environment: {{ .Values.environment }}
    version: {{ .Values.version }}
    component: frontend
spec:
  type: NodePort
  ports:
  - port: 6001
    targetPort: 6001
    protocol: TCP
    nodePort: 30007
  selector:
    app: countly-frontend

Not sure if this might work:

ports:
    - protocol: TCP
      port: 6001
      targetPort: 6001

Or if you could try changing targetPort to nodePort in your original

Let me clarify some misconceptions:

You cannot change the nodePort port range for a managed Kubernetes cluster like GKE.

A word about nodePort from official Kubernetes documentation:

NodePort: Exposes the Service on each Node’s IP at a static port (the NodePort). A ClusterIP Service, to which the NodePort Service routes, is automatically created. You’ll be able to contact the NodePort Service, from outside the cluster, by requesting <NodeIP>:<NodePort>.

-- Kubernetes.io: Services

nodePort port ranges from 30000 to 32767.

What you see here:

when I list the services on kubernetes I see this :

service/countly-frontend        NodePort       10.xx.xx.12    ><none>        6001:31145/TCP    110s

Specifically: 6001:31145/TCP is correct.

Example:

Assume that there is a pod with an application running on port 50001.

This is a service.yaml of above application:

apiVersion: v1
kind: Service
metadata:
  name: hello-service
spec:
  selector:
    app: hello
  ports:
    - name: hello-port
      port: 5678 # CLUSTER-IP PORT
      targetPort: 50001 # PORT WHICH YOUR APPLICATION IS RUNNING ON
      nodePort: 30051 # NODEPORT PORT 
  type: NodePort

Output of $ kubectl get services:

NAME               TYPE           CLUSTER-IP    EXTERNAL-IP                                           PORT(S)           AGE
hello-service      NodePort       10.86.1.195   <none>                                                5678:30051/TCP   25h

You will have an access to your application by:

• NodeIP:NodePort(30051) (external access)
• ClusterIP:port(5678) (internal access)
• PodIP:targetPort(50001) (internal access)

If you would like to expose your application on port 6001 for external use you can try a service type of LoadBalancer.

There are answers on StackOverflow that are going deeper in this topic:

• You can check what is exactly happening when creating a service object of type NodePort by looking on this answer.
• Services explanation from minikube perspective

Please take a look on official documentation about exposing applications on a GKE cluster: Cloud.google.com: Kubernetes engine: Exposing apps

Please let me know if you have any questions to that.