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Setting up ExternalDNS for Services on Azure

This tutorial describes how to setup ExternalDNS for usage within a Kubernetes cluster on Azure.

Make sure to use >=0.5.7 version of ExternalDNS for this tutorial.

This tutorial uses Azure CLI 2.0 for all Azure commands and assumes that the Kubernetes cluster was created via Azure Container Services and kubectl commands are being run on an orchestration node.

Creating an Azure DNS zone

The Azure provider for ExternalDNS will find suitable zones for domains it manages; it will not automatically create zones.

For this tutorial, we will create a Azure resource group named 'externaldns' that can easily be deleted later:

$ az group create -n externaldns -l eastus

Substitute a more suitable location for the resource group if desired.

Next, create a Azure DNS zone for "example.com":

$ az network dns zone create -g externaldns -n example.com

Substitute a domain you own for "example.com" if desired.

If using your own domain that was registered with a third-party domain registrar, you should point your domain's name servers to the values in the nameServers field from the JSON data returned by the az network dns zone create command. Please consult your registrar's documentation on how to do that.

Permissions to modify DNS zone

External-DNS needs permissions to make changes in the Azure DNS server. These permissions are defined in a Service Principal that should be made available to External-DNS as a configuration file.

The Azure DNS provider expects, by default, that the configuration file is at /etc/kubernetes/azure.json. This can be overridden with the --azure-config-file option when starting ExternalDNS.

Creating configuration file

The preferred way to inject the configuration file is by using a Kubernetes secret. The secret should contain an object named azure.json with content similar to this:

{
  "tenantId": "01234abc-de56-ff78-abc1-234567890def",
  "subscriptionId": "01234abc-de56-ff78-abc1-234567890def",
  "resourceGroup": "MyDnsResourceGroup",
  "aadClientId": "01234abc-de56-ff78-abc1-234567890def",
  "aadClientSecret": "uKiuXeiwui4jo9quae9o"
}

You can find the tenantId by running az account show --query "tenantId" or by selecting Azure Active Directory in the Azure Portal and checking the Directory ID under Properties.

You can find the subscriptionId by running az account show --query "id" or by selecting Subscriptions in the Azure Portal.

The resourceGroup is the Resource Group created in a previous step.

The aadClientID and aaClientSecret are associated with the Service Principal, that you need to create next.

Creating service principal

A Service Principal with a minimum access level of contributor to the DNS zone(s) and reader to the resource group containing the Azure DNS zone(s) is necessary for ExternalDNS to be able to edit DNS records. However, other more permissive access levels will work too (e.g. contributor to the resource group or the whole subscription).

This is an Azure CLI example on how to query the Azure API for the information required for the Resource Group and DNS zone you would have already created in previous steps.

> az login

Find the relevant subscription and make sure it is selected (the same subscriptionId should be set into azure.json)

> az account list
{
    "cloudName": "AzureCloud",
    "id": "<subscriptionId GUID>",
    "isDefault": false,
    "name": "My Subscription",
    "state": "Enabled",
    "tenantId": "AzureAD tenant ID",
    "user": {
      "name": "name",
      "type": "user"
}

# select the subscription
> az account set -s <subscriptionId GUID>
...

Create the service principal

> az ad sp create-for-rbac -n ExternalDnsServicePrincipal
{
  "appId": "appId GUID",  --> aadClientId value
  ...
  "password": "password",  --> aadClientSecret value
  "tenant": "AzureAD Tenant Id"  --> tenantId value
}

Assign the rights for the service principal

# find out the resource ids of the resource group where the dns zone is deployed, and the dns zone itself
> az group show --name externaldns
{
  "id": "/subscriptions/id/resourceGroups/externaldns",
  ...
}

> az network dns zone show --name example.com -g externaldns
{
  "id": "/subscriptions/.../resourceGroups/externaldns/providers/Microsoft.Network/dnszones/example.com",
  ...
}

# assign the rights to the created service principal, using the resource ids from previous step

# 1. as a reader to the resource group
> az role assignment create --role "Reader" --assignee <appId GUID> --scope <resource group resource id>  

# 2. as a contributor to DNS Zone itself
> az role assignment create --role "Contributor" --assignee <appId GUID> --scope <dns zone resource id>

Now you can create a file named 'azure.json' with values gathered above and with the structure of the example above. Use this file to create a Kubernetes secret:

$ kubectl create secret generic azure-config-file --from-file=/local/path/to/azure.json

Azure Managed Service Identity (MSI)

If Azure Managed Service Identity (MSI) is enabled for virtual machines, then there is no need to create separate service principal.

The contents of azure.json should be similar to this:

{
  "tenantId": "01234abc-de56-ff78-abc1-234567890def",
  "subscriptionId": "01234abc-de56-ff78-abc1-234567890def",
  "resourceGroup": "MyDnsResourceGroup",
  "useManagedIdentityExtension": true
}

If you have all the information necessary: create a file called azure.json containing the json structure above and substitute the values. Otherwise create a service principal as previously shown before creating the Kubernetes secret.

Then add the secret to the Kubernetes cluster before continuing:

kubectl create secret generic azure-config-file --from-file=azure.json

Deploy ExternalDNS

This deployment assumes that you will be using nginx-ingress. When using nginx-ingress do not deploy it as a Daemon Set. This causes nginx-ingress to write the Cluster IP of the backend pods in the ingress status.loadbalancer.ip property which then has external-dns write the Cluster IP(s) in DNS vs. the nginx-ingress service external IP.

Ensure that your nginx-ingress deployment has the following arg: added to it:

- --publish-service=namespace/nginx-ingress-controller-svcname

For more details see here: nginx-ingress external-dns

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: k8s.gcr.io/external-dns/external-dns:v0.7.6
        args:
        - --source=service
        - --source=ingress
        - --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
        - --provider=azure
        - --azure-resource-group=externaldns # (optional) use the DNS zones from the tutorial's resource group
        volumeMounts:
        - name: azure-config-file
          mountPath: /etc/kubernetes
          readOnly: true
      volumes:
      - name: azure-config-file
        secret:
          secretName: azure-config-file

Manifest (for clusters with RBAC enabled, cluster access)

apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1beta1
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/v1beta1
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: k8s.gcr.io/external-dns/external-dns:v0.7.6
        args:
        - --source=service
        - --source=ingress
        - --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
        - --provider=azure
        - --azure-resource-group=externaldns # (optional) use the DNS zones from the tutorial's resource group
        volumeMounts:
        - name: azure-config-file
          mountPath: /etc/kubernetes
          readOnly: true
      volumes:
      - name: azure-config-file
        secret:
          secretName: azure-config-file

Manifest (for clusters with RBAC enabled, namespace access)

This configuration is the same as above, except it only requires privileges for the current namespace, not for the whole cluster. However, access to nodes requires cluster access, so when using this manifest, services with type NodePort will be skipped!

apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: Role
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"]
---
apiVersion: rbac.authorization.k8s.io/v1beta1
kind: RoleBinding
metadata:
  name: external-dns
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: external-dns
subjects:
- kind: ServiceAccount
  name: 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:
      serviceAccountName: external-dns
      containers:
      - name: external-dns
        image: k8s.gcr.io/external-dns/external-dns:v0.7.6
        args:
        - --source=service
        - --source=ingress
        - --domain-filter=example.com # (optional) limit to only example.com domains; change to match the zone created above.
        - --provider=azure
        - --azure-resource-group=externaldns # (optional) use the DNS zones from the tutorial's resource group
        volumeMounts:
        - name: azure-config-file
          mountPath: /etc/kubernetes
          readOnly: true
      volumes:
      - name: azure-config-file
        secret:
          secretName: azure-config-file

Create the deployment for ExternalDNS:

$ kubectl create -f externaldns.yaml

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-svc
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 80
  selector:
    app: nginx
  type: ClusterIP

---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: nginx
  annotations:
    kubernetes.io/ingress.class: nginx
spec:
  rules:
  - host: server.example.com
    http:
      paths:
      - backend:
          serviceName: nginx-svc
          servicePort: 80
        path: /

When using external-dns with ingress objects it will automatically create DNS records based on host names specified in ingress objects that match the domain-filter argument in the external-dns deployment manifest. When those host names are removed or renamed the corresponding DNS records are also altered.

Create the deployment, service and ingress object:

$ kubectl create -f nginx.yaml

Since your external IP would have already been assigned to the nginx-ingress service, the DNS records pointing to the IP of the nginx-ingress service should be created within a minute.

Verifying Azure DNS records

Run the following command to view the A records for your Azure DNS zone:

$ az network dns record-set a list -g externaldns -z example.com

Substitute 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 ('@' indicates the record is for the zone itself).

Delete Azure Resource Group

Now that we have verified that ExternalDNS will automatically manage Azure DNS records, we can delete the tutorial's resource group:

$ az group delete -n externaldns