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Setting up ExternalDNS for Services on Azure

This tutorial describes how to setup ExternalDNS for Azure DNS with Azure Kubernetes Service.

Make sure to use >=0.11.0 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 MyDnsResourceGroup that can easily be deleted later:

$ az group create --name "MyDnsResourceGroup" --location "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 --resource-group "MyDnsResourceGroup" --name "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.

Configuration file

The azure provider will reference a configuration file called azure.json. 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"
}

The following fields are used:

  • tenantId (required) - run az account show --query "tenantId" or by selecting Azure Active Directory in the Azure Portal and checking the Directory ID under Properties.
  • subscriptionId (required) - run az account show --query "id" or by selecting Subscriptions in the Azure Portal.
  • resourceGroup (required) is the Resource Group created in a previous step that contains the Azure DNS Zone.
  • aadClientID and aaClientSecret are associated with the Service Principal. This is only used with Service Principal method documented in the next section.
  • useManagedIdentityExtension - this is set to true if you use either AKS Kubelet Identity or AAD Pod Identities methods documented in the next section.
  • userAssignedIdentityID - this contains the client id from the Managed identitty when using the AAD Pod Identities method documented in the next setion.

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.

Permissions to modify DNS zone

ExternalDNS needs permissions to make changes to the Azure DNS zone. There are three ways configure the access needed:

Service Principal

These permissions are defined in a Service Principal that should be made available to ExternalDNS as a configuration file azure.json.

Creating a service principal

A Service Principal with a minimum access level of DNS Zone Contributor or 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 (requires azure-cli and jq)

$ EXTERNALDNS_NEW_SP_NAME="ExternalDnsServicePrincipal" # name of the service principal
$ AZURE_DNS_ZONE_RESOURCE_GROUP="MyDnsResourceGroup" # name of resource group where dns zone is hosted
$ AZURE_DNS_ZONE="example.com" # DNS zone name like example.com or sub.example.com

# Create the service principal
$ DNS_SP=$(az ad sp create-for-rbac --name $EXTERNALDNS_NEW_SP_NAME)
$ EXTERNALDNS_SP_APP_ID=$(echo $DNS_SP | jq -r '.appId')
$ EXTERNALDNS_SP_PASSWORD=$(echo $DNS_SP | jq -r '.password')

Assign the rights for the service principal

Grant access to Azure DNS zone for the service principal.

# fetch DNS id used to grant access to the service principal
DNS_ID=$(az network dns zone show --name $AZURE_DNS_ZONE \
 --resource-group $AZURE_DNS_ZONE_RESOURCE_GROUP --query "id" --output tsv)

# 1. as a reader to the resource group
$ az role assignment create --role "Reader" --assignee $EXTERNALDNS_SP_APP_ID --scope $DNS_ID

# 2. as a contributor to DNS Zone itself
$ az role assignment create --role "Contributor" --assignee $EXTERNALDNS_SP_APP_ID --scope $DNS_ID

Creating a configuration file for the service principal

Create the file azure.json with values gather from previous steps.

cat <<-EOF > /local/path/to/azure.json
{
  "tenantId": "$(az account show --query tenantId -o tsv)",
  "subscriptionId": "$(az account show --query id -o tsv)",
  "resourceGroup": "$AZURE_DNS_ZONE_RESOURCE_GROUP",
  "aadClientId": "$EXTERNALDNS_SP_APP_ID",
  "aadClientSecret": "$EXTERNALDNS_SP_PASSWORD"
}
EOF

Use this file to create a Kubernetes secret:

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

Managed identity using AKS Kubelet identity

The managed identity that is assigned to the underlying node pool in the AKS cluster can be given permissions to access Azure DNS. Managed identities are essentially a service principal whose lifecycle is managed, such as deleting the AKS cluster will also delete the service principals associated with the AKS cluster. The managed identity assigned Kuberetes node pool, or specifically the VMSS, is called the Kubelet identity.

The managed identites were previously called MSI (Managed Service Identity) and are enabled by default when creating an AKS cluster.

Note that permissions granted to this identity will be accessible to all containers running inside the Kubernetes cluster, not just the ExternalDNS container(s).

For the managed identity, 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
}

Fetching the Kubelet identity

For this process, you will need to get the kublet identity:

$ PRINCIPAL_ID=$(az aks show --resource-group $CLUSTER_GROUP --name $CLUSTERNAME \
  --query "identityProfile.kubeletidentity.objectId" --output tsv)

Assign rights for the Kubelet identity

Grant access to Azure DNS zone for the kublet identity.

$ AZURE_DNS_ZONE="example.com" # DNS zone name like example.com or sub.example.com
$ AZURE_DNS_ZONE_RESOURCE_GROUP="MyDnsResourceGroup" # resource group where DNS zone is hosted

# fetch DNS id used to grant access to the kublet identity
$ DNS_ID=$(az network dns zone show --name $AZURE_DNS_ZONE \
  --resource-group $AZURE_DNS_ZONE_RESOURCE_GROUP --query "id" --output tsv)

$ az role assignment create --role "DNS Zone Contributor" --assignee $PRINCIPAL_ID --scope $DNS_ID

Creating a configuration file for the kubelet identity

Create the file azure.json with values gather from previous steps.

cat <<-EOF > /local/path/to/azure.json
{
  "tenantId": "$(az account show --query tenantId -o tsv)",
  "subscriptionId": "$(az account show --query id -o tsv)",
  "resourceGroup": "$AZURE_DNS_ZONE_RESOURCE_GROUP",
  "useManagedIdentityExtension": true
}
EOF

Use the azure.json file to create a Kubernetes secret:

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

Managed identity using AAD Pod Identities

For this process, we will create a managed identity that will be explicitly used by the ExternalDNS container. This process is similar to Kubelet identity except that this managed identity is not associated with the Kubernetes node pool, but rather associated with explicit ExternalDNS containers.

Enable the AAD Pod Identities feature

For this solution, AAD Pod Identities preview feature can be enabled. The commands below should do the trick to enable this feature:

$ az feature register --name EnablePodIdentityPreview --namespace Microsoft.ContainerService
$ az feature register --name AutoUpgradePreview --namespace Microsoft.ContainerService
$ az extension add --name aks-preview
$ az extension update --name aks-preview
$ az provider register --namespace Microsoft.ContainerService

Deploy the AAD Pod Identities service

Once enabled, you can update your cluster and install needed services for the AAD Pod Identities feature.

$ AZURE_AKS_RESOURCE_GROUP="my-aks-cluster-group" # name of resource group where aks cluster was created
$ AZURE_AKS_CLUSTER_NAME="my-aks-cluster" # name of aks cluster previously created

$ az aks update --resource-group ${AZURE_AKS_RESOURCE_GROUP} --name ${AZURE_AKS_CLUSTER_NAME} --enable-pod-identity

Note that, if you use the default network plugin kubenet, then you need to add the command line option --enable-pod-identity-with-kubenet to the above command.

Creating the managed identity

After this process is finished, create a managed identity.

$ IDENTITY_RESOURCE_GROUP=$AZURE_AKS_RESOURCE_GROUP # custom group or reuse AKS group
$ IDENTITY_NAME="example-com-identity"

# create a managed identity
$ az identity create --resource-group "${IDENTITY_RESOURCE_GROUP}" --name "${IDENTITY_NAME}"

Assign rights for the managed identity

Grant access to Azure DNS zone for the managed identity.

$ AZURE_DNS_ZONE_RESOURCE_GROUP="MyDnsResourceGroup" # name of resource group where dns zone is hosted
$ AZURE_DNS_ZONE="example.com" # DNS zone name like example.com or sub.example.com

# fetch identity client id from managed identity created earlier
$ IDENTITY_CLIENT_ID=$(az identity show --resource-group "${IDENTITY_RESOURCE_GROUP}" \
  --name "${IDENTITY_NAME}" --query "clientId" --output tsv)
# fetch DNS id used to grant access to the managed identity
$ DNS_ID=$(az network dns zone show --name "${AZURE_DNS_ZONE}" \
  --resource-group "${AZURE_DNS_ZONE_RESOURCE_GROUP}" --query "id" --output tsv)

$ az role assignment create --role "DNS Zone Contributor" \
  --assignee "${IDENTITY_CLIENT_ID}" --scope "${DNS_ID}"

Creating a configuration file for the managed identity

Create the file azure.json with the values from previous steps:

cat <<-EOF > /local/path/to/azure.json
{
  "tenantId": "$(az account show --query tenantId -o tsv)",
  "subscriptionId": "$(az account show --query id -o tsv)",
  "resourceGroup": "$AZURE_DNS_ZONE_RESOURCE_GROUP",
  "useManagedIdentityExtension": true,
  "userAssignedIdentityID": "$IDENTITY_CLIENT_ID"
}
EOF

Use the azure.json file to create a Kubernetes secret:

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

Creating an Azure identity binding

A binding between the managed identity and the ExternalDNS pods needs to be setup by creating AzureIdentity and AzureIdentityBinding resources. This will allow appropriately labeled ExternalDNS pods to authenticate using the managed identity. When AAD Pod Identity feature is enabled from previous steps above, the az aks pod-identity add can be used to create these resources:

$ IDENTITY_RESOURCE_ID=$(az identity show --resource-group ${IDENTITY_RESOURCE_GROUP} \
  --name ${IDENTITY_NAME} --query id --output tsv)

$ az aks pod-identity add --resource-group ${AZURE_AKS_RESOURCE_GROUP}  \
  --cluster-name ${AZURE_AKS_CLUSTER_NAME} --namespace "default" \
  --name "external-dns" --identity-resource-id ${IDENTITY_RESOURCE_ID}

This will add something similar to the following resouces:

apiVersion: aadpodidentity.k8s.io/v1
kind: AzureIdentity
metadata:
  labels:
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.azure.com/managedby: aks
  name: external-dns
spec:
  clientID: $IDENTITY_CLIENT_ID
  resourceID: $IDENTITY_RESOURCE_ID
  type: 0
---
apiVersion: aadpodidentity.k8s.io/v1
kind: AzureIdentityBinding
metadata:
  annotations:
  labels:
    addonmanager.kubernetes.io/mode: Reconcile
    kubernetes.azure.com/managedby: aks
  name: external-dns-binding
spec:
  azureIdentity: external-dns
  selector: external-dns

Update ExternalDNS labels

When deploying ExternalDNS, you want to make sure that deployed pod(s) will have the label aadpodidbinding: external-dns to enable AAD Pod Identities. You can patch an existing deployment of ExternalDNS with this command:

kubectl patch deployment external-dns --namespace "default" --patch \
 '{"spec": {"template": {"metadata": {"labels": {"aadpodidbinding": "external-dns"}}}}}'

Ingress used with 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

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.

The deployment assumes that ExternalDNS will be installed into the default namespace. If this namespace is different, the ClusterRoleBinding will need to be updated to reflect the desired alternative namespace, such as external-dns, kube-addons, etc.

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:v0.11.0
        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=MyDnsResourceGroup # (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/v1
kind: ClusterRole
metadata:
  name: external-dns
rules:
  - apiGroups: [""]
    resources: ["services","endpoints","pods", "nodes"]
    verbs: ["get","watch","list"]
  - apiGroups: ["extensions","networking.k8s.io"]
    resources: ["ingresses"]
    verbs: ["get","watch","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: k8s.gcr.io/external-dns/external-dns:v0.11.0
          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=MyDnsResourceGroup # (optional) use the DNS zones from the tutorial's resource group
            - --txt-prefix=externaldns-
          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/v1
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/v1
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:v0.11.0
          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=MyDnsResourceGroup # (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 --namespace "default" --filename externaldns.yaml

Deploying an Nginx Service

Create a 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:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: nginx-svc
                port:
                  number: 80

When using ExternalDNS 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 --namespace "default" --filename 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 --resource-group "MyDnsResourceGroup" --zone-name 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 --name "MyDnsResourceGroup"