Helm/Kubernetes - StatefulSet: is that possible use serviceAccount from different namespace - kubernetes

Question

Since the problem mentioned here.
I am wondering if it is possible to refer serviceAccountName: "test-sa" which is in namespace n2 for example to create statefulset in namespace n1
apiVersion: apps/v1beta1
kind: StatefulSet
metadata:
name: "{{.Values.ContainerName}}"
namespace: n1
labels:
name: "{{.Values.ReplicaName}}"
app: "{{.Values.ContainerName}}"
chart: "{{.Chart.Name}}-{{.Chart.Version}}"
annotations:
"helm.sh/created": {{.Release.Time.Seconds | quote }}
spec:
selector:
matchLabels:
app: "{{.Values.ContainerName}}"
serviceName: "{{.Values.ContainerName}}"
replicas: 2
template:
metadata:
labels:
app: "{{.Values.ContainerName}}"
spec:
serviceAccountName: "test-sa"
securityContext:
fsGroup: 26
terminationGracePeriodSeconds: 10
containers:
- name: {{.Values.ContainerName}}
image: "{{.Values.PostgresImage}}"
ports:
- containerPort: 5432
name: postgres
resources:
requests:
cpu: {{default "100m" .Values.Cpu}}
memory: {{default "100M" .Values.Memory}}
env:
- name: PGHOST
value: /tmp
- name: PG_PRIMARY_USER
value: primaryuser
- name: PG_MODE
value: set
- name: PG_PRIMARY_HOST
value: "{{.Values.PrimaryName}}"
- name: PG_PRIMARY_PORT
value: "5432"
- name: PG_PRIMARY_PASSWORD
value: "{{.Values.PrimaryPassword}}"
- name: PG_USER
value: testuser
- name: PG_PASSWORD
value: "{{.Values.UserPassword}}"
- name: PG_DATABASE
value: userdb
- name: PG_ROOT_PASSWORD
value: "{{.Values.RootPassword}}"
volumeMounts:
- name: pgdata
mountPath: "/pgdata"
readOnly: false
volumes:
- name: pgdata
persistentVolumeClaim:
claimName: {{.Values.PVCName}}

Answer 1

You can't; they need to be in the same namespace.
This is a more general rule. Whenever one object refers to another they generally need to be in the same namespace, or the target needs to be a cluster-global object. If a Pod references data in a ConfigMap or mounts a PersistentVolumeClaim, those need to be in the same namespace; if a Service selects Pods by label, those need to be in the same namespace. There are a couple of exceptions, notably around RBAC, but usually these things need to be deployed together.
In the context of a Helm chart, I'd just create a new ServiceAccount rather than trying to reuse an existing one. If it uses the typical {{ .Release.Name }}-{{ .Chart.Name }} naming pattern there won't generally be naming conflicts.