Networking Overview

Networking in Kubernetes is simple on the surface, but powerful under the hood. Every Pod gets an IP address, Services provide stable endpoints, and the network model enables communication across the entire cluster — often without needing to understand the low-level implementation details.

Core Principles of Kubernetes Networking

  1. Each Pod gets a unique IP
  2. No NAT between Pods

  3. All containers within a Pod share the same network namespace

  4. All Pods can reach each other

  5. Flat network model (no IP masquerading between Pods)

  6. Services provide stable access to Pods

  7. Pods are ephemeral — Services give them a consistent IP + DNS name

Network Abstraction Layers

Layer Purpose
Pod Network Every Pod gets an IP, routable in-cluster
Service Provides a stable endpoint for Pod groups
Ingress Exposes HTTP/S services externally
NetworkPolicy Controls traffic between Pods (optional)

DNS in Kubernetes

Kubernetes includes built-in DNS resolution for:

  • Services: my-service.my-namespace.svc.cluster.local
  • Pods (not recommended for direct use)

DNS is powered by CoreDNS by default, running in the kube-system namespace.

nslookup my-service.default.svc.cluster.local

Pod-to-Pod Communication

  • All Pods are routable via their internal IP addresses
  • No need for manual port forwarding
  • Backed by a Container Network Interface (CNI) plugin (e.g., Calico, Flannel)

Service Types (Covered in next section)

  • ClusterIP – default; internal-only
  • NodePort – exposes via node IP + static port
  • LoadBalancer – provision external LB (cloud)
  • ExternalName – maps to external DNS

Key Takeaways

  • Kubernetes assumes a flat, open network where every Pod can talk to every other Pod
  • You don’t need to assign IPs or manage routes — the CNI plugin does that
  • Communication is typically via Service abstraction, not direct Pod IPs
  • You can add NetworkPolicies to restrict traffic if needed

Summary

  • Every Pod gets an IP — networking is native, not container-to-container port mapping
  • Services, not Pods, are the preferred way to access applications
  • DNS is built-in and resolves Services by name
  • You don’t manage the network manually — but understanding its behavior is essential