I am trying to find our the minimum privileges required for application to communicate in kubernetes for the below scenarios

1. App1 is in namespace 1 and app2 is in namespace 2
2. App1 is in cluster 1 anf app2 is in cluster 2

I have deployed an sample application in my cluster (https://github.com/kubernetes/kubernetes/tree/release-1.2/examples/guestbook) in two different namespaces

However tough I associate these applications with service account have no privileges in respective namespaces , my php application is still able to reach redis application. I was expecting it to throw an error , how are my applications functioning even after giving my service account no roles

Below is the role i associated with my service account

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
metadata:
 name: no-access-cr
rules:
- apiGroups: [""] # "" indicates the core API group
  resources: [""] 
  verbs: [""]

Kindly assist!!!