Kubernetes Series: Networking Fundamentals

Kubernetes Networking

In this third part of our series, we’ll explore how networking works in Kubernetes.

Networking Model

Kubernetes imposes these fundamental requirements on the networking implementation:

1. All Pods can communicate with all other Pods without NAT
2. All Nodes can communicate with all Pods without NAT
3. The IP a Pod sees itself as is the same IP that others see it as

Pod-to-Pod Communication

Each Pod gets its own IP address. Communication between Pods in the same cluster happens directly.

CNI Plugins

Container Network Interface (CNI) plugins handle the networking:

• Flannel: Simple overlay network
• Calico: High-performance, BGP-based
• Cilium: eBPF-powered networking
• Weave: Easy to set up

Services

Services provide stable endpoints for Pods:

ClusterIP (Default)

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

NodePort

Exposes the service on each Node’s IP at a static port.

LoadBalancer

Provisions an external load balancer (cloud-dependent).

Ingress

Ingress manages external access to services:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-ingress
spec:
  rules:
  - host: myapp.example.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: my-service
            port:
              number: 80

Next Steps

In Part 4, we’ll cover persistent storage and StatefulSets.

Part 4: Storage and StatefulSets coming up!