From cybersecurity-skills
Implements Kubernetes NetworkPolicies for pod traffic segmentation with YAML for default deny, DNS egress, and service-to-service rules using Calico/Cilium CNIs.
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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.
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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.
# 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
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
# 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
# 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
# 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
# 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
# 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