Agent Skills: Managing Network Policies

Managing Network Policies

Overview

Create and manage Kubernetes NetworkPolicy manifests to enforce zero-trust networking between pods, namespaces, and external endpoints. Generate ingress and egress rules with label selectors, namespace selectors, CIDR blocks, and port specifications following the principle of least privilege.

Prerequisites

• Kubernetes cluster with a CNI plugin that supports NetworkPolicy (Calico, Cilium, Weave Net)
• kubectl configured with permissions to create and manage NetworkPolicy resources
• Pod labels consistently defined across deployments for accurate selector targeting
• Service communication map documenting which pods need to talk to which pods on which ports
• Understanding of DNS requirements (pods need egress to kube-dns on port 53 for name resolution)

Instructions

1. Map the application communication patterns: identify all service-to-service, service-to-database, and service-to-external connections
2. Start with a default-deny policy for both ingress and egress in each namespace to establish zero-trust baseline
3. Add explicit allow rules for each legitimate communication path: specify source pod labels, destination pod labels, and ports
4. Always include a DNS egress rule allowing traffic to kube-system namespace on UDP/TCP port 53 for CoreDNS
5. Define egress rules for external API access: use CIDR blocks or namespaceSelector for known external services
6. Apply policies to a test namespace first and verify connectivity with kubectl exec curl/wget commands
7. Monitor for blocked traffic in the CNI plugin logs (Calico: calicoctl node status, Cilium: cilium monitor)
8. Iterate on policies: add missing allow rules for any legitimate traffic that gets blocked
9. Document each policy with annotations explaining the business reason for the allowed communication

Output

• Default-deny NetworkPolicy manifests for ingress and egress per namespace
• Allow-list NetworkPolicy manifests for each service communication path
• DNS egress policy allowing pod name resolution
• External access egress policies with CIDR blocks
• Connectivity test commands for validation

Error Handling

| Error | Cause | Solution | |-------|-------|---------| | All traffic blocked after applying policy | Default-deny applied without corresponding allow rules | Apply allow rules before or simultaneously with deny policies; verify with kubectl exec tests | | DNS resolution fails after network policy | Missing egress rule for kube-dns/CoreDNS | Add egress policy allowing UDP and TCP port 53 to kube-system namespace | | Policy not targeting intended pods | Label mismatch between policy selector and pod labels | Verify labels with kubectl get pods --show-labels; match selectors exactly | | Traffic still allowed despite deny policy | CNI plugin does not support NetworkPolicy or policy in wrong namespace | Verify CNI support with kubectl get networkpolicy -A; ensure policy is in the correct namespace | | Intermittent connection failures | Policy allows traffic but connection pool or timeout settings too aggressive | Check if the issue is network policy or application-level; test with kubectl exec during failures |

Examples

• "Create a default-deny policy for the production namespace, then add allow rules so only the ingress controller can reach web pods on port 443."
• "Generate egress policies that restrict the API pods to communicate only with PostgreSQL (port 5432), Redis (port 6379), and external HTTPS APIs."
• "Build a complete set of network policies for a 3-tier app: frontend -> API (8080), API -> database (5432), API -> cache (6379), all pods -> DNS (53)."

Resources

• Kubernetes NetworkPolicy: https://kubernetes.io/docs/concepts/services-networking/network-policies/
• Calico network policy: https://docs.tigera.io/calico/latest/network-policy/
• Cilium network policy: https://docs.cilium.io/en/stable/security/policy/
• Network policy editor (visual): https://editor.networkpolicy.io/