AKS not creating KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT environment variables - kubernetes

Question

I've a Deployment and Service in AKS that also has a linked ServiceAccount that enables the pods to get, watch and list services.
In an AKS deployment this used to create the KUBERNETES_SERVICE_HOST and KUBERNETES_SERVICE_PORT environment variables with the pods. Now, it seems, it doesn't.
The only thing that's changed with that particular service/ deployment was various cluster updates at which some point it seems to have stopped working.
We've tried redeploying/ deleting and recreating the service, but nothing seems to work.
Here is the Deployment yaml:
apiVersion : apps/v1
kind: Deployment
metadata:
name: open-api
labels:
name: open-api
app: test-services
spec:
selector:
matchLabels:
name: open-api
app: test-services
strategy:
rollingUpdate:
maxUnavailable: 1
maxSurge: 1
minReadySeconds: 60
replicas: 1
template:
metadata:
labels:
name: open-api
app: test-services
spec:
serviceAccountName: open-api-account
containers:
- name: open-api
image: open-api
terminationMessagePolicy: FallbackToLogsOnError
ports:
- containerPort: 80
resources:
requests:
memory: "70Mi"
cpu: "50m"
limits:
memory: "150Mi"
cpu: "100m"
readinessProbe:
httpGet:
path: /pingz
port: 80
initialDelaySeconds: 10
periodSeconds: 3
env:
- name: "ASPNETCORE_ENVIRONMENT"
value: "$ENV_VAR"
Here's the yaml for the Service:
apiVersion: v1
kind: Service
metadata:
name: open-api
labels:
name: open-api
app: test-services
spec:
type: ClusterIP
ports:
- port: 80
selector:
name: open-api
app: test-services
Here's the yaml for the ServiceAccount:
apiVersion: v1
kind: ServiceAccount
metadata:
name: open-api-account
namespace: test-services
automountServiceAccountToken: false
---
kind: ClusterRole
apiVersion: rbac.authorization.k8s.io/v1
metadata:
namespace: test-services
name: open-api-service-reader
rules:
- apiGroups: [""] # "" indicates the core API group
resources: ["services"]
verbs: ["get", "watch", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
name: open-api-service-reader
namespace: test-services
subjects:
- kind: ServiceAccount
# Reference to ServiceAccount kind's `metadata.name`
name: open-api-account
# Reference to ServiceAccount kind's `metadata.namespace`
namespace: test-services
roleRef:
kind: ClusterRole
name: open-api-service-reader
apiGroup: rbac.authorization.k8s.io

Answer 1

These variables seem to be added automatically for pods that exist in kube-system. Not sure if this can be extended to other namespaces.