When I want to execute this command:

kubectl apply -f namespace.yaml

I had this error message:

The connection to the server localhost:8080 was refused - did you specify the right host or port?

Some answers have been posted in Stackoverflow like using kubectl with:

--kubeconfig=~/.kube/config

But this didn't solve my problem.

This is my namespace.yaml file:

apiVersion: v1
kind: Namespace
metadata:
  name: my_namespace

I'm using GKE (1.10.6-gke.3).