Kubernetes Network Policy Security: 6 Defense Patterns from Default Deny to Zero Trust

云原生

Is Your K8s Cluster Running Naked on the Network?

A default Kubernetes cluster allows all Pods to communicate freely—frontend Pods can directly access database Pods, test namespaces can reach production namespaces, and a compromised Pod can laterally move to any service in the cluster. In 2025, a financial company suffered a breach through a Pod with no network policy; the attacker moved laterally to the payment system within 30 minutes and stole 2 million user records. This isn't a movie plot—it's a real security incident.

Kubernetes NetworkPolicy is the cornerstone of cluster network security. From default deny to micro-segmentation, from Cilium eBPF to zero trust architecture, this article covers 6 defense patterns to ensure your cluster network is no longer exposed.

Core Concepts at a Glance

Concept Description Keywords
NetworkPolicy K8s native network policy resource, controls inter-Pod traffic ingress/egress, selector
Default Deny Deny all traffic by default, explicitly allow legitimate traffic whitelist, zero trust foundation
Micro-segmentation Fine-grained network isolation based on labels label selectors, namespace isolation
Cilium eBPF-based CNI plugin supporting L3-L7 policies eBPF, L7 policies, observability
eBPF Kernel-level programmable technology for high-performance network filtering kernel-space, zero-copy, XDP
mTLS Mutual TLS authentication for encrypted service-to-service communication cert rotation, identity verification
Zero Trust Zero trust network architecture: never trust, always verify continuous verification, least privilege

Deep Analysis: 5 Major K8s Network Security Challenges

Challenge Current State Risk Level Root Cause
Default allow-all No network restrictions between Pods in cluster 🔴 Critical K8s doesn't set NetworkPolicy by default
Lateral movement Attacker can access all services after breaching one Pod 🔴 Critical Lack of micro-segmentation policies
Policy explosion NetworkPolicy count spirals out of control in large clusters 🟡 Medium Poor label design
DNS dependency Service discovery relies on CoreDNS, DNS policies missing 🟡 Medium Overlooking DNS-layer security
Poor observability Network policy effectiveness hard to verify and audit 🟠 High Lack of policy audit tools

Pattern 1: Default Deny All Traffic

Default deny is the first step toward zero trust networking. In any namespace without NetworkPolicy, all Pods can communicate freely—this is the most dangerous state.

Namespace-Level Default Deny

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-ingress
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-egress
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Egress

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress

Allow DNS Resolution (Required for Egress)

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-dns-egress
  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

Batch Default Deny for All Namespaces

#!/bin/bash
NAMESPACES=$(kubectl get namespaces -o jsonpath='{.items[*].metadata.name}')

for ns in $NAMESPACES; do
  if [ "$ns" = "kube-system" ] || [ "$ns" = "kube-public" ]; then
    echo "Skipping system namespace: $ns"
    continue
  fi

  kubectl apply -f - <<EOF
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: $ns
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
EOF

  echo "Applied default-deny-all to namespace: $ns"
done

Verify Default Deny Policies

kubectl get networkpolicy -n production
kubectl describe networkpolicy default-deny-all -n production

kubectl run test-client --image=busybox:1.36 -n production --rm -it -- \
  wget -qO- --timeout=2 http://api-service.production.svc.cluster.local:8080

Pattern 2: Label-Based Micro-Segmentation

Micro-segmentation uses label selectors for fine-grained Pod access control—the core capability of NetworkPolicy.

Three-Tier Application Micro-Segmentation

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: frontend-policy
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: web
      tier: frontend
  policyTypes:
    - Ingress
    - Egress
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              env: production
          podSelector:
            matchLabels:
              app: ingress-nginx
      ports:
        - protocol: TCP
          port: 8080
        - protocol: TCP
          port: 8443
  egress:
    - to:
        - podSelector:
            matchLabels:
              app: api
              tier: backend
      ports:
        - protocol: TCP
          port: 8080
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: backend-policy
  namespace: production
spec:
  podSelector:
    matchLabels:
      app: api
      tier: backend
  policyTypes:
    - Ingress
    - Egress
  ingress:
    - from:
        - podSelector:
            matchLabels:
              app: web
              tier: frontend
      ports:
        - protocol: TCP
          port: 8080
  egress:
    - to:
        - podSelector:
            matchLabels:
              app: postgres
              tier: database
      ports:
        - protocol: TCP
          port: 5432
    - to:
        - podSelector:
            matchLabels:
              app: redis
              tier: cache
      ports:
        - protocol: TCP
          port: 6379
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: database-policy
  namespace: production
spec:
  podSelector:
    matchLabels:
      tier: database
  policyTypes:
    - Ingress
    - Egress
  ingress:
    - from:
        - podSelector:
            matchLabels:
              app: api
              tier: backend
      ports:
        - protocol: TCP
          port: 5432
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53

Cross-Namespace Policies

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-from-monitoring
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              purpose: monitoring
          podSelector:
            matchLabels:
              app: prometheus
      ports:
        - protocol: TCP
          port: 9090

Namespace Label Management

kubectl label namespace monitoring purpose=monitoring
kubectl label namespace staging env=staging
kubectl label namespace production env=production
kubectl label namespace kube-system kubernetes.io/metadata.name=kube-system

kubectl get namespaces --show-labels

Pattern 3: Cilium eBPF Advanced Network Policy

Cilium leverages eBPF to break through K8s native NetworkPolicy L3/L4 limitations, supporting L7 HTTP/gRPC/Kafka protocol policies.

Install Cilium

helm repo add cilium https://helm.cilium.io/
helm install cilium cilium/cilium \
  --namespace kube-system \
  --set kubeProxyReplacement=strict \
  --set hubble.enabled=true \
  --set hubble.relay.enabled=true \
  --set hubble.ui.enabled=true \
  --set operator.prometheus.enabled=true

L7 HTTP Policy

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: l7-http-policy
  namespace: production
spec:
  endpointSelector:
    matchLabels:
      app: api
      tier: backend
  ingress:
    - fromEndpoints:
        - matchLabels:
            app: web
            tier: frontend
      toPorts:
        - ports:
            - port: "8080"
              protocol: TCP
          rules:
            http:
              - method: GET
                path: "/api/v1/.*"
              - method: POST
                path: "/api/v1/orders"
              - method: PUT
                path: "/api/v1/orders/.*"

Kafka Protocol Policy

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: kafka-policy
  namespace: production
spec:
  endpointSelector:
    matchLabels:
      app: kafka
  ingress:
    - fromEndpoints:
        - matchLabels:
            app: order-service
      toPorts:
        - ports:
            - port: "9092"
              protocol: TCP
          rules:
            kafka:
              - role: produce
                topic: orders
              - role: consume
                topic: orders
    - fromEndpoints:
        - matchLabels:
            app: payment-service
      toPorts:
        - ports:
            - port: "9092"
              protocol: TCP
          rules:
            kafka:
              - role: produce
                topic: payments
              - role: consume
                topic: payments

DNS-Based Egress Policy

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: external-api-egress
  namespace: production
spec:
  endpointSelector:
    matchLabels:
      app: api
      tier: backend
  egress:
    - toFQDNs:
        - matchName: "api.stripe.com"
        - matchName: "api.sendgrid.com"
        - matchPattern: "*.amazonaws.com"
      toPorts:
        - ports:
            - port: "443"
              protocol: TCP
    - toEndpoints:
        - matchLabels:
            k8s:io.kubernetes.pod.namespace: kube-system
            k8s-app: kube-dns
      toPorts:
        - ports:
            - port: "53"
              protocol: UDP
          rules:
            dns:
              - matchPattern: "*"

Hubble Observability

cilium hubble port-forward &
hubble observe --namespace production --since 1m
hubble observe --namespace production --label app=api --verdict DROPPED
hubble observe --namespace production --http-path "/api/v1/.*" --method GET

Pattern 4: DNS-Based Network Policies

Native NetworkPolicy doesn't support domain-based policies, but Cilium and Calico extend this capability for more flexible egress control.

Cilium FQDN Policy

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: allow-external-services
  namespace: production
spec:
  endpointSelector:
    matchLabels:
      app: payment-service
  egress:
    - toFQDNs:
        - matchName: "api.stripe.com"
        - matchName: "api.paypal.com"
      toPorts:
        - ports:
            - port: "443"
              protocol: TCP
    - toFQDNs:
        - matchName: "s3.amazonaws.com"
        - matchPattern: "*.s3.amazonaws.com"
      toPorts:
        - ports:
            - port: "443"
              protocol: TCP
    - toEndpoints:
        - matchLabels:
            k8s:io.kubernetes.pod.namespace: kube-system
            k8s-app: kube-dns
      toPorts:
        - ports:
            - port: "53"
              protocol: UDP
          rules:
            dns:
              - matchPattern: "*"

Calico GlobalNetworkPolicy DNS Policy

apiVersion: projectcalico.org/v3
kind: GlobalNetworkPolicy
metadata:
  name: allow-external-dns
spec:
  selector: app == "payment-service"
  order: 100
  types:
    - Egress
  egress:
    - action: Allow
      protocol: TCP
      destination:
        domains:
          - "api.stripe.com"
          - "api.paypal.com"
        ports:
          - 443
    - action: Allow
      protocol: UDP
      destination:
        selector: k8s-app == "kube-dns"
        ports:
          - 53

DNS Policy Monitoring

cilium hubble observe --dns --namespace production
cilium hubble observe --fqdn "api.stripe.com" --namespace production

kubectl logs -n kube-system -l k8s-app=kube-dns --tail=100
kubectl get endpoints kube-dns -n kube-system

Pattern 5: Service Mesh mTLS

Service mesh implements automatic mTLS through sidecar proxies, providing encryption and identity verification for service-to-service communication.

Istio Strict mTLS Mode

apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: default
  namespace: istio-system
spec:
  mtls:
    mode: STRICT

apiVersion: security.istio.io/v1beta1
kind: PeerAuthentication
metadata:
  name: backend-mtls
  namespace: production
spec:
  selector:
    matchLabels:
      tier: backend
  mtls:
    mode: STRICT
  portLevelMtls:
    8080:
      mode: STRICT

Istio AuthorizationPolicy

apiVersion: security.istio.io/v1beta1
kind: AuthorizationPolicy
metadata:
  name: backend-authz
  namespace: production
spec:
  selector:
    matchLabels:
      app: api
      tier: backend
  rules:
    - from:
        - source:
            principals:
              - "cluster.local/ns/production/sa/frontend"
      to:
        - operation:
            methods: ["GET", "POST"]
            paths: ["/api/v1/*"]
    - from:
        - source:
            namespaces: ["monitoring"]
            principals:
              - "cluster.local/ns/monitoring/sa/prometheus"
      to:
        - operation:
            methods: ["GET"]
            paths: ["/metrics"]

Cilium Cluster Mesh mTLS

apiVersion: cilium.io/v2
kind: CiliumClusterwideNetworkPolicy
metadata:
  name: allow-mtls-traffic
spec:
  endpointSelector: {}
  ingress:
    - fromRequires:
        - matchLabels:
            io.cilium.k8s.policy.serviceaccount: frontend
      toPorts:
        - ports:
            - port: "8080"
              protocol: TCP
  ingress:
    - fromEndpoints:
        - matchLabels:
            io.cilium.k8s.policy.serviceaccount: monitoring
      toPorts:
        - ports:
            - port: "9090"
              protocol: TCP

Certificate Management

istioctl analyze -n production
istioctl proxy-config secret deploy/frontend.production

kubectl get certificates -n production
kubectl describe certificate backend-cert -n production

kubectl logs -n istio-system -l app=citadel --tail=50

Pattern 6: Zero Trust Network Architecture Blueprint

Zero trust isn't a single technology—it's a security architecture philosophy: never trust, always verify, least privilege.

Zero Trust Network Architecture Layering

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: zero-trust-foundation
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
  ingress:
    - from:
        - podSelector: {}
      ports: []
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53

Zero Trust Identity Layer

apiVersion: cilium.io/v2
kind: CiliumNetworkPolicy
metadata:
  name: identity-based-policy
  namespace: production
spec:
  endpointSelector:
    matchLabels:
      app: api
      tier: backend
      env: production
  ingress:
    - fromRequires:
        - matchLabels:
            app: web
            tier: frontend
            env: production
            io.cilium.k8s.policy.serviceaccount: frontend-sa
      toPorts:
        - ports:
            - port: "8080"
              protocol: TCP
          rules:
            http:
              - method: GET
                path: "/api/v1/.*"
              - method: POST
                path: "/api/v1/orders"

Zero Trust Audit Layer

apiVersion: audit.k8s.io/v1
kind: Policy
rules:
  - level: RequestResponse
    resources:
      - group: networking.k8s.io
        resources: ["networkpolicies"]
    verbs: ["create", "update", "delete"]
  - level: Metadata
    resources:
      - group: cilium.io
        resources: ["ciliumnetworkpolicies", "ciliumclusterwidenetworkpolicies"]
    verbs: ["create", "update", "delete"]

Zero Trust Observability

cilium hubble observe --namespace production --type trace --type drop
cilium hubble observe --verdict DROPPED --since 5m --namespace production

kubectl get ciliumnetworkpolicies -A
kubectl get ciliumclusterwidenetworkpolicies
kubectl get networkpolicies -A

cilium connectivity test --namespace production

Zero Trust Architecture Verification Script

#!/bin/bash
echo "=== Zero Trust Network Audit ==="

echo "[1] Checking default deny policies..."
for ns in $(kubectl get ns -o jsonpath='{.items[*].metadata.name}'); do
  count=$(kubectl get networkpolicy -n "$ns" 2>/dev/null | grep -c "default-deny" || true)
  if [ "$count" -eq 0 ] && [ "$ns" != "kube-system" ]; then
    echo "  WARNING: No default-deny policy in namespace: $ns"
  fi
done

echo "[2] Checking mTLS status..."
istioctl proxy-config secret -n production 2>/dev/null || echo "  Istio not installed or no proxies found"

echo "[3] Checking Cilium policy status..."
cilium policy get 2>/dev/null || echo "  Cilium not available"

echo "[4] Checking for overly permissive policies..."
kubectl get networkpolicies -A -o json | \
  python3 -c "
import json, sys
policies = json.load(sys.stdin)
for p in policies.get('items', []):
    ns = p['metadata']['namespace']
    name = p['metadata']['name']
    ingress = p.get('spec', {}).get('ingress', [])
    for i in ingress:
        if not i.get('from') and not i.get('ports'):
            print(f'  WARNING: {ns}/{name} has empty ingress from selector')
    egress = p.get('spec', {}).get('egress', [])
    for e in egress:
        if not e.get('to') and not e.get('ports'):
            print(f'  WARNING: {ns}/{name} has empty egress to selector')
"

echo "=== Audit Complete ==="

5 Common Pitfalls

Pitfall 1: Forgetting to Allow DNS Traffic

# ❌ Wrong: After denying all egress, DNS resolution also fails
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress

# ✅ Correct: Must explicitly allow DNS egress
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53

Pitfall 2: Missing Namespace Labels

# ❌ Wrong: namespaceSelector matches no namespaces
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-monitoring
spec:
  podSelector: {}
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              purpose: monitoring

# ✅ Correct: Label the namespace first
# kubectl label namespace monitoring purpose=monitoring
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-monitoring
spec:
  podSelector: {}
  ingress:
    - from:
        - namespaceSelector:
            matchLabels:
              purpose: monitoring
          podSelector:
            matchLabels:
              app: prometheus

Pitfall 3: CNI Doesn't Support NetworkPolicy

# ❌ Wrong: Flannel doesn't support NetworkPolicy, policies won't take effect
# Using flannel as CNI

# ✅ Correct: Use a NetworkPolicy-capable CNI
# kubectl get pods -n kube-system -l k8s-app=calico-node
# kubectl get pods -n kube-system -l k8s-app=cilium
# kubectl get pods -n kube-system -l app=antrea

Pitfall 4: Policy Ordering Causes Override

# ❌ Wrong: Allow policy first then deny policy—deny doesn't override allow
# NetworkPolicy is additive with no priority concept

# ✅ Correct: NetworkPolicy uses a whitelist model, all policies are additive
# For priority, use Calico GlobalNetworkPolicy or Cilium policies
# Calico supports the order field for priority control
apiVersion: projectcalico.org/v3
kind: GlobalNetworkPolicy
metadata:
  name: deny-suspicious
spec:
  order: 50
  selector: all()
  types:
    - Ingress
  ingress:
    - action: Deny
      source:
        selector: app == "compromised-service"

Pitfall 5: Ignoring the kube-system Namespace

# ❌ Wrong: Applying default deny to kube-system breaks cluster functionality
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: kube-system
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress

# ✅ Correct: kube-system needs special handling—allow necessary traffic
# Skip default deny for kube-system namespace
# Or set precise allow policies for critical components in kube-system
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: kube-system-allow
  namespace: kube-system
spec:
  podSelector:
    matchLabels:
      k8s-app: kube-dns
  policyTypes:
    - Ingress
  ingress:
    - from: []
      ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53

Error Troubleshooting Table

Error Symptom Possible Cause Diagnostic Command Solution
Pods can't communicate Default deny policy too restrictive kubectl get networkpolicy -A Add precise ingress/egress rules
Service discovery fails DNS egress blocked kubectl exec -it <pod> -- nslookup api-service Add DNS egress allow rule
NetworkPolicy not taking effect CNI doesn't support it kubectl get pods -n kube-system -l k8s-app Switch to Calico/Cilium/Antrea
Cross-namespace access denied Namespace missing labels kubectl get ns --show-labels Add required labels to namespace
Hubble can't observe Cilium Hubble not enabled cilium status Enable Hubble during Helm install
mTLS connection fails Certificate expired or not issued istioctl proxy-config secret <pod> Check Certificate resource status
L7 policy not working Cilium version too low cilium version Upgrade to Cilium 1.14+
DNS policy not working CoreDNS version too low kubectl get deploy coredns -n kube-system -o yaml Upgrade CoreDNS
Policy count explosion Poor label design kubectl get networkpolicy -A | wc -l Redesign label taxonomy
Calico policy conflicts GlobalNetworkPolicy priority issues calicoctl get globalnetworkpolicy -o yaml Adjust order field

Advanced Optimization

Policy as Code (PaC)

Manage NetworkPolicy with GitOps to ensure policy changes go through code review:

git checkout -b feature/add-network-policy

mkdir -p k8s/network-policies/production

cat > k8s/network-policies/production/default-deny.yaml << 'EOF'
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: default-deny-all
  namespace: production
spec:
  podSelector: {}
  policyTypes:
    - Ingress
    - Egress
  egress:
    - to:
        - namespaceSelector:
            matchLabels:
              kubernetes.io/metadata.name: kube-system
      ports:
        - protocol: UDP
          port: 53
        - protocol: TCP
          port: 53
EOF

git add . && git commit -m "feat: add default deny policy for production"
git push origin feature/add-network-policy

Automated Policy Testing

cilium connectivity test \
  --test "echo-ingress-l7" \
  --namespace production \
  --force-deploy

kubectl run policy-test \
  --image=busybox:1.36 \
  -n production \
  --rm -it -- \
  wget -qO- --timeout=2 http://api-service:8080/healthz

kubectl run dns-test \
  --image=busybox:1.36 \
  -n production \
  --rm -it -- \
  nslookup api-service.production.svc.cluster.local

Policy Performance Optimization

cilium config | grep policy

cilium bpf policy list

kubectl get ciliumnetworkpolicies -A -o json | \
  python3 -c "
import json, sys
policies = json.load(sys.stdin)
print(f'Total CiliumNetworkPolicies: {len(policies.get(\"items\", []))}')
for p in policies.get('items', []):
    ns = p['metadata']['namespace']
    name = p['metadata']['name']
    ingress = len(p.get('spec', {}).get('ingress', []))
    egress = len(p.get('spec', {}).get('egress', []))
    print(f'  {ns}/{name}: ingress={ingress}, egress={egress}')
"

CNI Plugin Comparison

Feature Calico Cilium Antrea Weave Net
NetworkPolicy support ✅ Full ✅ Full+L7 ✅ Full ⚠️ Basic
L7 policies ❌ ✅ HTTP/gRPC/Kafka ❌ ❌
FQDN policies ✅ ✅ ❌ ❌
eBPF dataplane ✅ Optional ✅ Default ✅ Optional ❌
Observability ❌ ✅ Hubble ⚠️ Flow Exporter ❌
Encryption ✅ WireGuard ✅ WireGuard/IPsec ✅ IPsec ✅ IPsec
Performance High Very High High Medium
Multi-cluster ✅ ✅ Cluster Mesh ✅ ❌
Service Mesh ❌ ✅ Built-in ❌ ❌
Community activity High Very High High Low
Use case General production High perf + L7 vSphere environments Dev/test

Summary

Kubernetes network security isn't built overnight—it's a progressive hardening process. Start with default deny, implement micro-segmentation step by step, introduce Cilium eBPF for L7 capabilities, control external access through DNS policies, leverage service mesh for mTLS, and ultimately build a zero trust network architecture. Each step shrinks the attack surface; each layer adds defense depth. Remember: a K8s cluster without NetworkPolicy is an attacker's playground.

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