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Setting up ExternalDNS using AWS Service Discovery API

This tutorial describes how to set up ExternalDNS for usage within a Kubernetes cluster on AWS with Service Discovery API.

The Service Discovery API is an alternative approach to managing DNS records directly using the Route53 API. It is more suitable for a dynamic environment where service endpoints change frequently. It abstracts away technical details of the DNS protocol and offers a simplified model. Service discovery consists of three main API calls:

  • CreatePublicDnsNamespace – automatically creates a DNS hosted zone
  • CreateService – creates a new named service inside the specified namespace
  • RegisterInstance/DeregisterInstance – can be called multiple times to create a DNS record for the specified Service

Learn more about the API in the Amazon Route 53 API Reference.

IAM Permissions

To use the service discovery API, a user executing the ExternalDNS must have the permissions in the AmazonRoute53AutoNamingFullAccess managed policy.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "route53:GetHostedZone",
                "route53:ListHostedZonesByName",
                "route53:CreateHostedZone",
                "route53:DeleteHostedZone",
                "route53:ChangeResourceRecordSets",
                "route53:CreateHealthCheck",
                "route53:GetHealthCheck",
                "route53:DeleteHealthCheck",
                "route53:UpdateHealthCheck",
                "ec2:DescribeVpcs",
                "ec2:DescribeRegions",
                "servicediscovery:*"
            ],
            "Resource": [
                "*"
            ]
        }
    ]
}

Set up a namespace

Create a DNS namespace using the service discovery API

$ aws servicediscovery create-public-dns-namespace --name "external-dns-test.my-org.com"

Verify that the namespace was truly created

$ aws servicediscovery list-namespaces

Deploy ExternalDNS

Connect your kubectl client to the cluster that you want to test ExternalDNS with. Then apply the following manifest file to deploy ExternalDNS.

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: external-dns
spec:
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: external-dns
    spec:
      containers:
      - name: external-dns
        image: registry.opensource.zalan.do/teapot/external-dns:v0.5.3
        args:
        - --source=service
        - --source=ingress
        - --domain-filter=external-dns-test.my-org.com # Makes ExternalDNS see only the namespaces that match the specified domain. Omit the filter if you want to process all available namespaces.
        - --provider=aws-sd
        - --aws-zone-type=public # Only look at public namespaces. Valid values are public, private, or no value for both)
        - --txt-owner-id=my-identifier

Verify that ExternalDNS works (Service example)

Create the following sample application to test that ExternalDNS works.

For services ExternalDNS will look for the annotation external-dns.alpha.kubernetes.io/hostname on the service and use the corresponding value.

apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com
spec:
  type: LoadBalancer
  ports:
  - port: 80
    name: http
    targetPort: 80
  selector:
    app: nginx

---

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: nginx
spec:
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
          name: http

After one minute check that a corresponding DNS record for your service was created in your hosted zone. We recommended that you use the Amazon Route53 console for that purpose.

Custom TTL

The default DNS record TTL (time to live) is 300 seconds. You can customize this value by setting the annotation external-dns.alpha.kubernetes.io/ttl. For example, modify the service manifest YAML file above:

apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: nginx.external-dns-test.my-org.com
    external-dns.alpha.kubernetes.io/ttl: 60
spec:
    ...

This will set the TTL for the DNS record to 60 seconds.

Clean up

Delete all service objects before terminating the cluster so all load balancers get cleaned up correctly.

$ kubectl delete service nginx

Give ExternalDNS some time to clean up the DNS records for you. Then delete the remaining service and namespace.

$ aws servicediscovery list-services

{
    "Services": [
        {
            "Id": "srv-6dygt5ywvyzvi3an",
            "Arn": "arn:aws:servicediscovery:us-west-2:861574988794:service/srv-6dygt5ywvyzvi3an",
            "Name": "nginx"
        }
    ]
}
$ aws servicediscovery delete-service --id srv-6dygt5ywvyzvi3an
$ aws servicediscovery list-namespaces
{
    "Namespaces": [
        {
            "Type": "DNS_PUBLIC",
            "Id": "ns-durf2oxu4gxcgo6z",
            "Arn": "arn:aws:servicediscovery:us-west-2:861574988794:namespace/ns-durf2oxu4gxcgo6z",
            "Name": "external-dns-test.my-org.com"
        }
    ]
}
$ aws servicediscovery delete-namespace --id ns-durf2oxu4gxcgo6z