💡 Quick Answer: networking

The Problem

This is one of the most searched Kubernetes topics with thousands of monthly searches. A comprehensive, production-ready guide prevents hours of trial and error.

The Solution

Create ClusterIP Service

apiVersion: v1
kind: Service
metadata:
  name: api-service
spec:
  type: ClusterIP       # Default type (can be omitted)
  selector:
    app: api
  ports:
    - name: http
      port: 80           # Service port (what clients connect to)
      targetPort: 8080   # Container port
    - name: grpc
      port: 9090
      targetPort: 9090

How It Works

# Service gets a virtual IP (ClusterIP)
kubectl get svc api-service
# NAME          TYPE        CLUSTER-IP     PORT(S)
# api-service   ClusterIP   10.96.45.123   80/TCP,9090/TCP

# DNS resolution (from any pod)
nslookup api-service.default.svc.cluster.local
# → 10.96.45.123

# Short DNS names work within same namespace
curl http://api-service/endpoint
curl http://api-service.default/endpoint           # Cross-namespace
curl http://api-service.default.svc.cluster.local  # Fully qualified

# kube-proxy creates iptables/IPVS rules
# ClusterIP → random backend pod (round-robin)

Service Discovery

# Environment variables (auto-injected)
# API_SERVICE_SERVICE_HOST=10.96.45.123
# API_SERVICE_SERVICE_PORT=80

# DNS (preferred — always works)
# api-service.namespace.svc.cluster.local

Multi-Port Services

spec:
  ports:
    - name: http       # Name required when multiple ports
      port: 80
      targetPort: 8080
    - name: metrics
      port: 9090
      targetPort: 9090

graph TD
    A[Pod A: curl api-service:80] --> B[CoreDNS resolves to 10.96.45.123]
    B --> C[kube-proxy iptables/IPVS]
    C --> D[Pod B: 10.244.1.5:8080]
    C --> E[Pod C: 10.244.2.8:8080]
    C --> F[Pod D: 10.244.3.12:8080]

Frequently Asked Questions

ClusterIP vs headless?

ClusterIP gives you a virtual IP with kube-proxy load balancing. Headless (clusterIP: None) returns pod IPs directly — no load balancing, client chooses. Use headless for StatefulSets.

Can I access ClusterIP from outside?

No — ClusterIP is internal only. Use kubectl port-forward for dev access, NodePort for basic external access, or LoadBalancer/Ingress for production.

Best Practices

Start with the simplest configuration that solves your problem
Test in staging before production
Use kubectl describe and events for troubleshooting
Document team conventions for consistency

Key Takeaways

This is fundamental Kubernetes operational knowledge
Follow established conventions and recommended labels
Monitor and iterate based on real production behavior
Automate repetitive tasks to reduce human error

Kubernetes ClusterIP Service Explained