Kubernetes Networking

Introduction:

Kubernetes is known for its powerful orchestration capabilities — but behind every container and pod is a complex networking model that keeps everything connected. In this post, we’ll break it down simply and clearly.

What Is Kubernetes Networking?

Kubernetes networking enables communication between containers, pods, services, and external networks. It’s responsible for how applications running in different pods or clusters talk to each other and the outside world.

While Kubernetes abstracts away infrastructure complexity, understanding networking is essential for:

• Debugging connectivity issues

• Securing traffic

• Scaling applications effectively

 Key Concepts in Kubernetes Networking:

1. Pod-to-Pod Communication

• Every pod in a Kubernetes cluster gets its own unique IP address.

• Pods can talk to each other directly using these IPs.

• Kubernetes assumes a flat network, meaning all pods can reach each other without NAT (Network Address Translation).

2. Service Networking

Pods are ephemeral — they can die and restart with new IPs. That’s where Kubernetes Services come in.

• A Service is an abstraction that gives a stable IP and DNS name to a group of pods.

• It uses selectors to route traffic to the right pods.

Common service types:

• ClusterIP: Internal-only access (default)

• NodePort: Exposes service on a static port on each node

• LoadBalancer: Integrates with cloud provider load balancers

• ExternalName: Maps service to an external DNS name.

3. DNS in Kubernetes

Kubernetes has an internal DNS service (usually CoreDNS) that:

• Resolves service names to their IPs

• Supports automatic DNS entries for Services and Pods.

4. Ingress and Egress

Ingress and egress define how traffic enters and exits the Kubernetes cluster.

Ingress:

• Acts like a reverse proxy for HTTP/S traffic

• Routes external traffic to internal services

• Usually requires an Ingress Controller (e.g., NGINX, Traefik, Istio)

Egress:

• Controls how traffic leaves the cluster

• Often managed using Network Policies or service mesh tools.

5. Network Policies

Network policies control who can talk to whom inside the cluster. Without them, everything can talk to everything — which is a security risk.

You can define policies to:

• Deny all traffic except specific ports or labels

• Isolate sensitive applications

• Limit egress to specific domains or IPs.

Popular CNI Plugins:

Kubernetes relies on CNI plugins for implementing its networking model. Popular options include:

• Flannel – Simple and easy to set up

• Calico – Great for security and network policies

• Cilium – Based on eBPF, advanced security features

• Weave Net – Mesh-based networking with encryption

 Best Practices for Kubernetes Networking:

• Use DNS names, not IPs, for service discovery

• Enforce Network Policies from day one

• Use Ingress Controllers with HTTPS and TLS termination

• Monitor traffic using service meshes like Istio or Linkerd

• Avoid hardcoding ports or IPs in your code.

Conclusion:

Kubernetes networking may seem complex at first, but once you grasp the basics — Pods, Services, Ingress, and DNS — everything starts to click. Whether you're deploying microservices or scaling enterprise apps, a strong foundation in Kubernetes networking ensures better security, performance, and resilience.