Amazon EKS — Services & DNS

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Services & DNS

Kubernetes Services provide stable networking endpoints for your pods. CoreDNS handles service discovery so pods can find each other by name.

Service Types

Type Accessibility Use Case
ClusterIP Internal only Default; internal microservice communication
NodePort External via node IP:port Testing; rarely used in production
LoadBalancer External via AWS ELB/NLB Production external access
ExternalName DNS CNAME Pointing to external services

ClusterIP (Default)

apiVersion: v1
kind: Service
metadata:
  name: backend
spec:
  type: ClusterIP     # Default
  selector:
    app: backend
  ports:
    - port: 80
      targetPort: 8080

# Other pods can reach it via:
$ curl http://backend            # Same namespace
$ curl http://backend.default    # Cross-namespace (short)
$ curl http://backend.default.svc.cluster.local  # FQDN

CoreDNS

CoreDNS runs as a Deployment in kube-system and provides DNS for all Services:

DNS Resolution
┌────────────────────────────────────────────────┐
│  Pod queries: "backend"                        │
│       │                                        │
│       ▼                                        │
│  CoreDNS (kube-system)                         │
│  Checks: backend.default.svc.cluster.local     │
│       │                                        │
│       ▼                                        │
│  Returns: 172.20.45.67 (ClusterIP)             │
└────────────────────────────────────────────────┘

DNS for Pods

# Pod DNS name (if hostname set):
<pod-ip-with-dashes>.<namespace>.pod.cluster.local
# Example: 10-0-1-11.default.pod.cluster.local

Troubleshooting DNS

# Test DNS resolution from a pod
$ kubectl run dns-test --image=busybox:1.36 --rm -it -- nslookup kubernetes
Server:    172.20.0.10
Address:   172.20.0.10:53
Name:      kubernetes.default.svc.cluster.local
Address:   172.20.0.1

# Check CoreDNS pods
$ kubectl get pods -n kube-system -l k8s-app=kube-dns

# Check CoreDNS config
$ kubectl get configmap coredns -n kube-system -o yaml

Common Mistakes

Mistake Impact
Using pod IPs directly Breaks when pods restart
Wrong targetPort Service routes to wrong port
CoreDNS not running All DNS resolution fails
Not using headless Services for StatefulSets Can’t address individual pods

What’s Next?

Secure pod communication: Network Policies.

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