ExternalDNS

Learn how to install and use ExternalDNS

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ExternalDNS synchronizes exposed Kubernetes Services and Ingresses with DNS providers.

Before getting into the chart’s possibilities, let’s start by deploying the default configuration:

helm install <release-name> oci://dp.apps.rancher.io/charts/external-dns \
  --set global.imagePullSecrets={application-collection}

Check our authentication guide if you need to configure Application Collection OCI credentials in your Kubernetes cluster.

Chart overview

Our ExternalDNS chart stems from the official external-secrets chart and is adapted to include our best practices. As such, any chart-related documentation provided by upstream will work out of the box with our chart. You can check the official documentation here.

Chart configuration

To view the supported configuration options and documentation, run:

helm show values oci://dp.apps.rancher.io/charts/external-dns

Configure a DNS provider

ExternalDNS supports multiple DNS providers implemented by the ExternalDNS contributors, though not every implementation has the same stability level. Check the official documentation for the current status of the providers.

We will use AWS for this guide. The main steps to properly configure our ExternalDNS chart with AWS as a provider are:

Create an IAM user allowed to modify Route53.
Configure the chart with AWS credentials.
Set up an AWS hosted zone.

We will skip the steps on properly configuring your aws CLI and provision a Kubernetes cluster given they fall outside the scope of this guide. You can check the related AWS documentation if you want to start from the basics.

Before deploying ExternalDNS, we will create an IAM policy that allows ExternalDNS to update Route53 Resource Record Sets and Hosted Zones.

cat <<EOF > ./route53_policy.json
{
  "Version": "2025-01-01",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "route53:ChangeResourceRecordSets"
      ],
      "Resource": [
        "arn:aws:route53:::hostedzone/*"
      ]
    },
    {
      "Effect": "Allow",
      "Action": [
        "route53:ListHostedZones",
        "route53:ListResourceRecordSets",
        "route53:ListTagsForResource"
      ],
      "Resource": [
        "*"
      ]
    }
  ]
}
EOF

aws iam create-policy --policy-name "AllowExternalDNSUpdates" --policy-document file://route53_policy.json
export POLICY_ARN=$(aws iam list-policies \
  --query 'Policies[?PolicyName==`AllowExternalDNSUpdates`].Arn' --output text)

You must use the above policy (represented by the POLICY_ARN environment variable) to allow ExternalDNS to update records in Route53 DNS zones. We will do so by creating a new IAM user and retrieving its static credentials:

aws iam create-user --user-name "externaldns"
aws iam attach-user-policy --user-name "externaldns" --policy-arn $POLICY_ARN
export AWS_ACCESS_KEY=$(aws iam create-access-key --user-name "externaldns")
export AWS_ACCESS_KEY_ID=$(echo $AWS_ACCESS_KEY | jq -r '.AccessKey.AccessKeyId')
export AWS_SECRET_ACCESS_KEY=$(echo $AWS_ACCESS_KEY | jq -r '.AccessKey.SecretAccessKey')

Now that the credentials are ready, we should make them available for our chart. We will use a Kubernetes Secret to do so:

kubectl create secret generic aws-credentials-secret \
  --from-literal=access-key=$AWS_ACCESS_KEY_ID \
  --from-literal=secret-access-key=$AWS_SECRET_ACCESS_KEY

You are now almost ready to deploy our ExternalDNS chart. The last step to do so will be configuring the chart to use aws as the DNS provider and access its credentials:

cat <<EOF > ./external-dns.yaml
provider:
  name: aws
env:
  - name: AWS_DEFAULT_REGION
    value: eu-central-1
  - name: AWS_ACCESS_KEY_ID
    valueFrom:
      secretKeyRef:
        name: aws-credentials-secret
        key: access-key
  - name: AWS_SECRET_ACCESS_KEY
    valueFrom:
      secretKeyRef:
        name: aws-credentials-secret
        key: secret-access-key
EOF

You can now install the chart using the custom values previously defined:

helm upgrade --install <release-name> oci://dp.apps.rancher.io/charts/external-dns \
  --set global.imagePullSecrets={application-collection} \
  --values external-dns.yaml

As the final step to configure your AWS DNS provider, you should create a hosted zone. This can be easily done via the aws CLI:

aws route53 create-hosted-zone --name "applicationcollectionexample.com." \
  --caller-reference "external-dns-test-$(date +%s)"

The hosted zone will take a few minutes to be ready. Once it is deployed, you will be able to check that your ExternalDNS deployment has also updated its configuration:

$ kubectl logs external-dns-78bf44bb7c-w5b84
...
time="2025-01-01T11:11:11Z" level=info msg="Instantiating new Kubernetes client"
time="2025-01-01T11:11:11Z" level=info msg="Using inCluster-config based on serviceaccount-token"
time="2025-01-01T11:11:11Z" level=info msg="Created Kubernetes client https://10.100.0.1:443"
...
time="2025-01-01T11:11:11Z" level=info msg="Applying provider record filter for domains: [applicationcollectionexample.com. .applicationcollectionexample.com.]"
time="2025-01-01T11:11:11Z" level=info msg="All records are already up to date"

Operations

Manage a service via ExternalDNS

In this example, we assume you have configured an AWS provider as explained in the Configure a DNS provider section. We will deploy an NGINX container and expose it via a LoadBalancer service. If properly configured, external-dns will manage the service and create the necessary DNS records in the provider. You will need to run the following commands to create the described resources:

$ kubectl create service loadbalancer nginx --tcp=80:80
service/nginx created
$ kubectl annotate service nginx external-dns.alpha.kubernetes.io/hostname='applicationcollectionexample.com'
service/nginx annotated
$ kubectl run nginx --image dp.apps.rancher.io/containers/nginx:1.26 \
  --labels=app=nginx \
  --overrides='{"spec": {"imagePullSecrets":[{"name": "application-collection"}]}}'
pod/nginx created

Be aware of the external-dns annotation included in the service, which is required for the ExternalDNS chart to manage the service.

AWS will take a couple of minutes to create the DNS records. Afterward, you can check the updated changes both in our external-dns pod and the AWS console:

$ kubectl logs --selector=app.kubernetes.io/name=external-dns
...
time="2025-01-01T11:11:11Z" level=info msg="Applying provider record filter for domains: [applicationcollectionexample.com. .applicationcollectionexample.com.]"
time="2025-01-01T11:11:11Z" level=info msg="Desired change: CREATE applicationcollectionexample.com A" profile=default zoneID=/hostedzone/Z0626846S566SWBNEQ2H zoneName=applicationcollectionexample.com.
time="2025-01-01T11:11:11Z" level=info msg="Desired change: CREATE applicationcollectionexample.com TXT" profile=default zoneID=/hostedzone/Z0626846S566SWBNEQ2H zoneName=applicationcollectionexample.com.
time="2025-01-01T11:11:11Z" level=info msg="2 record(s) were successfully updated" profile=default zoneID=/hostedzone/Z0626846S566SWBNEQ2H zoneName=applicationcollectionexample.com.

$ aws route53 list-resource-record-sets --output json --hosted-zone-id $ZONE_ID

Uninstall the chart

Removing an installed ExternalDNS instance is simple:

helm uninstall <release-name>

Remember to remove any AWS resource you deployed during this guide.

Last modified January 30, 2025