Kubernetes Networking Demystified: Services, Ingress, and Network Policies

Introduction

Kubernetes networking is often cited as one of the most challenging aspects of container orchestration. This guide covers the three pillars: Services, Ingress, and Network Policies.

Services: Stable Endpoints for Dynamic Pods

ClusterIP Services

apiVersion: v1
kind: Service
metadata:
  name: backend-api
spec:
  type: ClusterIP
  selector:
    app: backend
  ports:
  - port: 80
    targetPort: 8080

LoadBalancer Services

apiVersion: v1
kind: Service
metadata:
  name: public-api
spec:
  type: LoadBalancer
  selector:
    app: api
  ports:
  - port: 443
    targetPort: 8443

Ingress: HTTP/HTTPS Traffic Management

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: app-ingress
spec:
  ingressClassName: nginx
  tls:
  - hosts:
    - app.example.com
    secretName: app-tls-secret
  rules:
  - host: app.example.com
    http:
      paths:
      - path: /api
        pathType: Prefix
        backend:
          service:
            name: backend-api
            port:
              number: 80

Network Policies: Securing Pod Communication

Default Deny All

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

Allow Specific Ingress

apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-frontend-to-backend
spec:
  podSelector:
    matchLabels:
      app: backend
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: frontend
    ports:
    - protocol: TCP
      port: 8080

Troubleshooting

# Check endpoints
kubectl get endpoints my-service

# Test DNS
kubectl exec -it my-pod -- nslookup kubernetes.default

# Debug with netshoot
kubectl run netshoot --image=nicolaka/netshoot -it --rm -- bash

Conclusion

Master Services, Ingress, and Network Policies, and you'll have a solid foundation for building secure, scalable applications on Kubernetes.

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Originally published at instadevops.com