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Setting up ExternalDNS for Pi-hole

This tutorial describes how to setup ExternalDNS to sync records with Pi-hole's Custom DNS. Pi-hole has an internal list it checks last when resolving requests. This list can contain any number of arbitrary A or CNAME records. There is a pseudo-API exposed that ExternalDNS is able to use to manage these records.

Deploy ExternalDNS

You can skip to the manifest if authentication is disabled on your Pi-hole instance or you don't want to use secrets.

If your Pi-hole server's admin dashboard is protected by a password, you'll likely want to create a secret first containing its value. This is optional since you do retain the option to pass it as a flag with --pihole-password.

You can create the secret with:

kubectl create secret generic pihole-password \
    --from-literal EXTERNAL_DNS_PIHOLE_PASSWORD=supersecret

Replacing "supersecret" with the actual password to your Pi-hole server.

ExternalDNS Manifest

Apply the following manifest to deploy ExternalDNS, editing values for your environment accordingly. Be sure to change the namespace in the ClusterRoleBinding if you are using a namespace other than default.

---
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","watch"]
---
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:v0.13.5
        # If authentication is disabled and/or you didn't create
        # a secret, you can remove this block.
        envFrom:
        - secretRef:
            # Change this if you gave the secret a different name
            name: pihole-password
        args:
        - --source=service
        - --source=ingress
        # Pihole only supports A/CNAME records so there is no mechanism to track ownership.
        # You don't need to set this flag, but if you leave it unset, you will receive warning
        # logs when ExternalDNS attempts to create TXT records.
        - --registry=noop
        # IMPORTANT: If you have records that you manage manually in Pi-hole, set
        # the policy to upsert-only so they do not get deleted.
        - --policy=upsert-only
        - --provider=pihole
        # Change this to the actual address of your Pi-hole web server
        - --pihole-server=http://pihole-web.pihole.svc.cluster.local
      securityContext:
        fsGroup: 65534 # For ExternalDNS to be able to read Kubernetes token files

Arguments

  • --pihole-server (env: EXTERNAL_DNS_PIHOLE_SERVER) - The address of the Pi-hole web server
  • --pihole-password (env: EXTERNAL_DNS_PIHOLE_PASSWORD) - The password to the Pi-hole web server (if enabled)
  • --pihole-tls-skip-verify (env: EXTERNAL_DNS_PIHOLE_TLS_SKIP_VERIFY) - Skip verification of any TLS certificates served by the Pi-hole web server.

Verify ExternalDNS Works

Ingress Example

Create an Ingress resource. ExternalDNS will use the hostname specified in the Ingress object.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: foo
spec:
  ingressClassName: nginx
  rules:
  - host: foo.bar.com
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: foo
            port:
              number: 80

Service Example

The below sample application can be used to verify Services work. 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.homelab.com
spec:
  type: LoadBalancer
  ports:
  - port: 80
    name: http
    targetPort: 80
  selector:
    app: nginx
---
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
          name: http

You can then query your Pi-hole to see if the record was created.

Change @192.168.100.2 to the actual address of your DNS server

$ dig +short @192.168.100.2  nginx.external-dns-test.homelab.com

192.168.100.129