Explanation:

To create an internal load balancer, create a service manifest named internal-lb.yaml with the service type LoadBalancer and the azure-load-balancer-internal annotation as shown in the following example:
YAML:
apiVersion: v1
kind: Service
metadata:
name: internal-app
annotations:
service.beta.kubernetes.io/azure-load-balancer-internal: "true"
spec:
type: LoadBalancer
ports:
- port: 80
selector:
app: internal-app
References:
https://docs.microsoft.com/en-us/azure/aks/internal-lb