Kubernetes networking can seem like magic — until something breaks. Understanding the networking model is essential for debugging and designing reliable systems.

The Kubernetes Network Model

Every Pod gets its own IP address. The fundamental rules:

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

CNI Plugins

The Container Network Interface (CNI) is the abstraction layer. Popular choices:

• Cilium: eBPF-based, high performance, built-in observability
• Calico: Mature, supports BGP for bare metal
• Flannel: Simple overlay network, good for getting started

Service Discovery

Kubernetes Services provide stable endpoints:

• ClusterIP: Internal-only virtual IP
• NodePort: Exposes on each node’s IP
• LoadBalancer: Provisions a cloud load balancer
• Headless: DNS-only, for StatefulSets

Service Mesh

For complex microservice architectures, a service mesh adds:

• mTLS between all services (zero-trust networking)
• Traffic splitting and canary deployments
• Distributed tracing and metrics
• Circuit breaking and retry policies

Istio remains the most feature-rich option, while Linkerd offers simplicity and lower resource overhead.

Debugging Tips

• kubectl exec into a pod and use curl/nslookup for basic connectivity
• Use cilium connectivity test or equivalent for your CNI
• Check NetworkPolicies — they’re often the silent blocker