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Setting up ExternalDNS for Services on Linode

This tutorial describes how to setup ExternalDNS for usage within a Kubernetes cluster using Linode DNS Manager.

Make sure to use >=0.5.5 version of ExternalDNS for this tutorial.

Managing DNS with Linode

If you want to learn about how to use Linode DNS Manager read the following tutorials:

An Introduction to Managing DNS, and general documentation

Creating Linode Credentials

Generate a new oauth token by following the instructions at Access-and-Authentication

The environment variable LINODE_TOKEN will be needed to run ExternalDNS with Linode.

Deploy ExternalDNS

Connect your kubectl client to the cluster you want to test ExternalDNS with. Then apply one of the following manifests file to deploy ExternalDNS.

Manifest (for clusters without RBAC enabled)

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:v0.14.2
        args:
        - --source=service # ingress is also possible
        - --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
        - --provider=linode
        env:
        - name: LINODE_TOKEN
          value: "YOUR_LINODE_API_KEY"

Manifest (for clusters with RBAC enabled)

apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: external-dns
rules:
- apiGroups: [""]
  resources: ["services","endpoints","pods"]
  verbs: ["get","watch","list"]
- apiGroups: ["extensions","networking.k8s.io"]
  resources: ["ingresses"]
  verbs: ["get","watch","list"]
- apiGroups: [""]
  resources: ["nodes"]
  verbs: ["list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: external-dns-viewer
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: external-dns
subjects:
- kind: ServiceAccount
  name: external-dns
  namespace: default
---
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:
      serviceAccountName: external-dns
      containers:
      - name: external-dns
        image: registry.k8s.io/external-dns/external-dns:v0.14.2
        args:
        - --source=service # ingress is also possible
        - --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
        - --provider=linode
        env:
        - name: LINODE_TOKEN
          value: "YOUR_LINODE_API_KEY"

Deploying an Nginx Service

Create a service file called 'nginx.yaml' with the following contents:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        name: nginx
        ports:
        - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
  annotations:
    external-dns.alpha.kubernetes.io/hostname: my-app.example.com
spec:
  selector:
    app: nginx
  type: LoadBalancer
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80

Note the annotation on the service; use the same hostname as the Linode DNS zone created above.

ExternalDNS uses this annotation to determine what services should be registered with DNS. Removing the annotation will cause ExternalDNS to remove the corresponding DNS records.

Create the deployment and service:

$ kubectl create -f nginx.yaml

Depending where you run your service it can take a little while for your cloud provider to create an external IP for the service.

Once the service has an external IP assigned, ExternalDNS will notice the new service IP address and synchronize the Linode DNS records.

Verifying Linode DNS records

Check your Linode UI to view the records for your Linode DNS zone.

Click on the zone for the one created above if a different domain was used.

This should show the external IP address of the service as the A record for your domain.

Cleanup

Now that we have verified that ExternalDNS will automatically manage Linode DNS records, we can delete the tutorial's example:

$ kubectl delete service -f nginx.yaml
$ kubectl delete service -f externaldns.yaml