Managing Network Policies

Prerequisites

Before using this skill, ensure:

• Kubernetes cluster has network policy support enabled
• Network plugin supports policies (Calico, Cilium, Weave)
• Pod labels are properly defined for policy selectors
• Understanding of application communication patterns
• Namespace isolation strategy is defined

Instructions

1. Identify Requirements: Determine which pods need to communicate
2. Define Selectors: Use pod/namespace labels for policy targeting
3. Configure Ingress: Specify allowed incoming traffic sources and ports
4. Configure Egress: Define allowed outgoing traffic destinations
5. Test Policies: Verify connectivity works as expected
6. Monitor Denials: Check for blocked traffic in network plugin logs
7. Iterate: Refine policies based on application behavior

Output

Network Policy Examples:

# {baseDir}/network-policies/allow-frontend-to-backend.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend-to-backend
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: backend
  policyTypes:
    - Ingress
  ingress:
    - from:
      - podSelector:
          matchLabels:
            app: frontend
      ports:
      - protocol: TCP
        port: 8080
---
# Deny all ingress by default
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-ingress
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress

Egress Policy:

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-external-api
spec:
  podSelector:
    matchLabels:
      app: api-client
  policyTypes:
    - Egress
  egress:
    - to:
      - namespaceSelector:
          matchLabels:
            name: external-services
      ports:
      - protocol: TCP
        port: 443

Error Handling

Policy Not Applied

• Error: Traffic still blocked/allowed contrary to policy
• Solution: Verify network plugin supports policies and policy is applied to correct namespace

DNS Resolution Fails

• Error: Pods cannot resolve DNS after applying policy
• Solution: Add egress rule allowing DNS traffic to kube-dns/coredns

No Communication After Policy

• Error: All traffic blocked unexpectedly
• Solution: Check for default-deny policies and ensure explicit allow rules exist

Label Mismatch

• Error: Policy not targeting intended pods
• Solution: Verify pod labels match policy selectors using kubectl get pods --show-labels

Resources

• Kubernetes NetworkPolicy: https://kubernetes.io/docs/concepts/services-networking/network-policies/
• Calico documentation: https://docs.projectcalico.org/
• Example policies in {baseDir}/network-policy-examples/