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Setting up ExternalDNS for ExternalName Services

This tutorial describes how to setup ExternalDNS for usage in conjunction with an ExternalName service.

Use cases

The main use cases that inspired this feature is the necessity for having a subdomain pointing to an external domain. In this scenario, it makes sense for the subdomain to have a CNAME record pointing to the external domain.

Setup

External DNS

apiVersion: apps/v1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  selector:
    matchLabels:
      app: external-dns
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      containers:
      - name: external-dns
        image: registry.k8s.io/external-dns/external-dns:v0.14.0
        args:
        - --log-level=debug
        - --source=service
        - --source=ingress
        - --namespace=dev
        - --domain-filter=example.org.
        - --provider=aws
        - --registry=txt
        - --txt-owner-id=dev.example.org

ExternalName Service

kind: Service
apiVersion: v1
metadata:
  name: aws-service
  annotations:
    external-dns.alpha.kubernetes.io/hostname: tenant1.example.org,tenant2.example.org
spec:
  type: ExternalName
  externalName: aws.example.org

This will create 2 CNAME records pointing to aws.example.org:

tenant1.example.org
tenant2.example.org

ExternalName Service with an IP address

If externalName is an IP address, External DNS will create A records instead of CNAME.

kind: Service
apiVersion: v1
metadata:
  name: aws-service
  annotations:
    external-dns.alpha.kubernetes.io/hostname: tenant1.example.org,tenant2.example.org
spec:
  type: ExternalName
  externalName: 111.111.111.111

This will create 2 A records pointing to 111.111.111.111:

tenant1.example.org
tenant2.example.org

Last update: November 11, 2023
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