Implementing Network Policies For Kubernetes

---
name: implementing-network-policies-for-kubernetes
description: Use when kubernetes NetworkPolicies provide pod-level network segmentation
  by defining ingress and egress rules that control traffic flow between pods, namespaces,
  and external endpoints. Combined with CNI plu. Use when working with implementing
  network policies for kubernetes.
domain: cybersecurity
subdomain: container-security
tags:
- containers
- kubernetes
- security
- network-policies
- microsegmentation
version: '1.0'
author: oyi77
license: Apache-2.0
nist_csf:
- PR.PS-01
- PR.IR-01
- ID.AM-08
- DE.CM-01
category: cybersecurity
---

# Implementing Network Policies for Kubernetes

## Overview

Kubernetes NetworkPolicies provide pod-level network segmentation by defining ingress and egress rules that control traffic flow between pods, namespaces, and external endpoints. Combined with CNI plugins like Calico or Cilium, network policies enforce zero-trust microsegmentation to prevent lateral movement within the cluster.


## When to Use
**Trigger phrases:**
- "implementing network policies for kubernetes"
- "Kubernetes NetworkPolicies provide pod-level network segmentation by defining in"


- When deploying or configuring implementing network policies for kubernetes capabilities in your environment
- When establishing security controls aligned to compliance requirements
- When building or improving security architecture for this domain
- When conducting security assessments that require this implementation

## Prerequisites

- Kubernetes cluster with NetworkPolicy-supporting CNI (Calico, Cilium, Antrea)
- kubectl configured with admin access
- Understanding of pod labels and selectors

## Workflow

1. **Scope the task** — define objectives, boundaries, and success criteria
2. **Gather information** — collect all necessary data and context before proceeding
3. **Execute the core workflow** — follow the domain-specific steps methodically
4. **Validate results** — verify outputs against expected outcomes or baselines
5. **Document findings** — record results, anomalies, and recommendations
### Step 1: Default Deny All Traffic

```yaml
# default-deny-all.yaml - Apply to every namespace
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: production
spec:
  podSelector: {}  # Applies to all pods
  policyTypes:
    - Ingress
    - Egress
```

### Step 2: Allow DNS Egress (Required for Service Discovery)

```yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-dns
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Egress
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53
```

### Step 3: Application-Specific Policies

```yaml
# Allow frontend to reach backend only
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: backend-allow-frontend
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: backend
  policyTypes:
    - Ingress
  ingress:
    - from:
        - podSelector:
            matchLabels:
              app: frontend
      ports:
        - protocol: TCP
          port: 8080
---
# Allow backend to reach database only
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: database-allow-backend
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: database
  policyTypes:
    - Ingress
  ingress:
    - from:
        - podSelector:
            matchLabels:
              app: backend
      ports:
        - protocol: TCP
          port: 5432
```

### Step 4: Cross-Namespace Policies

```yaml
# Allow monitoring namespace to scrape metrics
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-monitoring-scrape
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              purpose: monitoring
      ports:
        - protocol: TCP
          port: 9090  # Prometheus metrics port
```

### Step 5: Egress Restrictions

```yaml
# Restrict egress to specific external services
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: restrict-egress
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: backend
  policyTypes:
    - Egress
  egress:
    - to:
        - podSelector:
            matchLabels:
              app: database
      ports:
        - protocol: TCP
          port: 5432
    - to:  # Allow external API
        - ipBlock:
            cidr: 203.0.113.0/24
      ports:
        - protocol: TCP
          port: 443
    - to:  # DNS
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53
```

### Step 6: Block Cloud Metadata Access

```yaml
# Prevent SSRF to cloud metadata service
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: block-metadata
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Egress
  egress:
    - to:
        - ipBlock:
            cidr: 0.0.0.0/0
            except:
              - 169.254.169.254/32  # AWS/GCP metadata
              - 100.100.100.200/32  # Azure metadata
```

## Validation Commands

```bash
# Verify policies are applied
kubectl get networkpolicies -n production

# Test connectivity (should be blocked)
kubectl run test-pod --image=busybox --restart=Never -n production -- wget -qO- --timeout=2 http://database-service:5432
# Expected: timeout (blocked by policy)

# Test allowed traffic
kubectl run frontend-test --image=busybox --labels=app=frontend --restart=Never -n production -- wget -qO- --timeout=2 http://backend-service:8080
# Expected: connection succeeds
```

## When NOT to Use

- You need to test the implementation (use performing-* skills)
- Task is about configuring existing tools (use configuring-* skills)
- You need to analyze security events (use analyzing-* skills)
- Task is about building detection rules (use building-* skills)
- You don't have access to the target environment
- Task requires vendor-specific expertise (consult vendor docs)


## Red Flags

- Performing actions without explicit written authorization from the asset owner
- Testing against production systems without a defined scope and rules of engagement
- Capturing traffic on networks without authorization or privacy considerations
- Leaving packet captures containing sensitive data unencrypted on disk
- Deploying inline blocking rules without testing for false positives first

## Verification

- All steps executed successfully against a test environment before production use
- Output documented with screenshots or logs demonstrating expected behavior
- Captures verified as complete with no dropped packets
- Detection rules tested against known-benign traffic for false positive rate
- Alert thresholds validated and tuned to reduce noise

## References

- [Kubernetes Network Policies](https://kubernetes.io/docs/concepts/services-networking/network-policies/)
- [Calico Network Policies](https://docs.tigera.io/calico/latest/network-policy/)
- [Cilium Network Policies](https://docs.cilium.io/en/stable/security/policy/)
- [Network Policy Editor](https://editor.networkpolicy.io/)

## Process

1. Analyze the task requirements
2. Apply domain expertise
3. Verify output quality

## Anti-Rationalization Table

| Rationalization | Reality |
|---|---|
| "We are too small to be targeted" | Automated attacks target everyone. Size does not matter. |
| "Security slows us down" | A breach slows you down 100x more. Build security in from the start. |
| "We will fix it after launch" | Vulnerabilities in production are exploited within hours. Fix before deploy. |