np-front-to-back.yaml

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: pod-frontend
  namespace: default
spec:
  podSelector:
    matchLabels:
      run: frontend
  policyTypes:
    - Egress
  egress:
    - to:
        - podSelector:
            matchLabels:
              run: backend
---
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: pod-backend
  namespace: default
spec:
  podSelector:
    matchLabels:
      run: backend
  policyTypes:
    - Ingress
    - Egress
  ingress:
    - from:
        - podSelector:
            matchLabels:
              run: frontend
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              id: cassandra