Implementing Network Policies for Kubernetes

Genel Bakış

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.

Ne Zaman Kullanılır

• Dağıt:ing yaparken or configuring implementing network policies for kubernetes capabilities in your environment
• establishing yaparken: security controls aligned to compliance requirements
• building yaparken or improving security architecture for this domain
• conducting yaparken security assessments that require this implementation

Ön Gereksinimler

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

İş Akışı

Adım 1: Default Deny All Traffic

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

Adım 2: Allow DNS Egress (Required for Service Discovery)

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

Adım 3: Application-Specific Policies

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
---
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

Adım 4: Cross-Namespace Policies

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

Adım 5: Egress Restrictions

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

Adım 6: Block Cloud Metadata Access

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

Doğrulama Commands

kubectl get networkpolicies -n production

kubectl run test-pod --image=busybox --restart=Never -n production -- wget -qO- --timeout=2 http://database-service:5432

kubectl run frontend-test --image=busybox --labels=app=frontend --restart=Never -n production -- wget -qO- --timeout=2 http://backend-service:8080

References

• Kubernetes Network Policies
• Calico Network Policies
• Cilium Network Policies
• Network Policy Editor

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