Cross namespaced access

How to provide namespaced acces to a service account of other namespace?

Problem:

Let, we have two namespaces A and B. We want to provide access of some resources of namespace B to a ServiceAccount of namespace A.

Solution:

Create a RoleBinding in namespace B with subject pointing to ServiceAccount of namespace A.

kind: RoleBinding
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  name: demo
  namespace: B
subjects:
- kind: ServiceAccount
  name: demo-sa
  namespace: A
roleRef:
  kind: Role
  name: demo-role
  apiGroup: rbac.authorization.k8s.io