Can I connect one service account to multiple namespaces in Kubernetes?

Question

I have couple of namespaces - assume NS1 and NS2. I have serviceaccounts created in those - sa1 in NS1 and sa2 in NS2. I have created roles and rolebindings for sa1 to do stuff within NS1 and sa2 within NS2. What I want is give sa1 certain access within NS2 (say only Pod Reader role).

I am wondering if that's possible or not?

Solution

You can simply reference a ServiceAccount from another namespace in the RoleBinding:

apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
metadata:
  name: pod-reader
  namespace: ns2
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "list", "watch"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: pod-reader-from-ns1
  namespace: ns2
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: pod-reader
subjects:
- kind: ServiceAccount
  name: ns1-service-account
  namespace: ns1