External DNS for Kubernetes: Setup Guide

💡 Quick Answer: networking

The Problem

Engineers need production-ready guides for these essential Kubernetes ecosystem tools. Incomplete documentation leads to misconfiguration and security gaps.

The Solution

Install ExternalDNS

helm repo add external-dns https://kubernetes-sigs.github.io/external-dns
helm install external-dns external-dns/external-dns \
  --namespace external-dns --create-namespace \
  --set provider.name=aws \
  --set env[0].name=AWS_DEFAULT_REGION \
  --set env[0].value=eu-west-1 \
  --set policy=sync \
  --set domainFilters[0]=example.com

How It Works

# Create a Service or Ingress with a hostname annotation
apiVersion: v1
kind: Service
metadata:
  name: web
  annotations:
    external-dns.alpha.kubernetes.io/hostname: app.example.com
    external-dns.alpha.kubernetes.io/ttl: "300"
spec:
  type: LoadBalancer
  selector:
    app: web
  ports:
    - port: 80
# ExternalDNS automatically creates:
# app.example.com → A record → LoadBalancer IP

Works with Ingress Too

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: web-ingress
spec:
  rules:
    - host: app.example.com     # ExternalDNS picks this up automatically
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: web
                port:
                  number: 80

Provider Configuration

Policies

graph LR
    A[Service/Ingress with hostname] --> B[ExternalDNS watches]
    B --> C{DNS Provider}
    C --> D[Route53]
    C --> E[Cloudflare]
    C --> F[Google DNS]
    G[Service deleted] --> B
    B -->|policy=sync| H[DNS record deleted]

Frequently Asked Questions

Will ExternalDNS delete my manually created records?

With policy=sync, it manages records it created (tracked via TXT ownership records). It won’t touch records created outside ExternalDNS. Use upsert-only for extra safety.

Best Practices

• Start with default configurations and customize as needed
• Test in a non-production cluster first
• Monitor resource usage after deployment
• Keep components updated for security patches

Key Takeaways

• This tool fills a critical gap in the Kubernetes ecosystem
• Follow the principle of least privilege for all configurations
• Automate where possible to reduce manual errors
• Monitor and alert on operational metrics