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STACKIT Webhook - ExternalDNS

ExternalDNS serves as an add-on for Kubernetes designed to automate the management of Domain Name System (DNS) records for Kubernetes services by utilizing various DNS providers. While Kubernetes traditionally manages DNS records internally, ExternalDNS augments this functionality by transferring the responsibility of DNS records management to an external DNS provider such as STACKIT. Consequently, the STACKIT webhook enables the management of your STACKIT domains within your Kubernetes cluster using ExternalDNS.

For utilizing ExternalDNS with STACKIT, it is mandatory to establish a STACKIT project, a service account within the project, generate an authentication token for the service account, authorize the service account to create and read dns zones, and finally, establish a STACKIT zone.

Kubernetes Deployment

The STACKIT webhook is presented as a standard Open Container Initiative (OCI) image released in the GitHub container registry. The deployment is compatible with all Kubernetes-supported methods. The subsequent example demonstrates the deployment as a sidecar container within the ExternalDNS pod.

# We create a Secret from an auth token. Alternatively, you can also
# use keys to authenticate the webhook - see "Authentication" below.
kubectl create secret generic external-dns-stackit-webhook --from-literal=auth-token='<Your-Token>'

kubectl apply -f - <<EOF
apiVersion: v1
kind: ServiceAccount
metadata:
  name: external-dns
  namespace: default
  labels:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
---
apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: external-dns
  labels:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
rules:
  - apiGroups: [""]
    resources: ["nodes"]
    verbs: ["list","watch"]
  - apiGroups: [""]
    resources: ["pods"]
    verbs: ["get","watch","list"]
  - apiGroups: [""]
    resources: ["services","endpoints"]
    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
  labels:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: external-dns
subjects:
  - kind: ServiceAccount
    name: external-dns
    namespace: default
---
apiVersion: v1
kind: Service
metadata:
  name: external-dns
  namespace: default
  labels:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
spec:
  type: ClusterIP
  selector:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
  ports:
    - name: http
      port: 7979
      targetPort: http
      protocol: TCP
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: external-dns
  namespace: default
  labels:
    app.kubernetes.io/name: external-dns
    app.kubernetes.io/instance: external-dns
spec:
  replicas: 1
  selector:
    matchLabels:
      app.kubernetes.io/name: external-dns
      app.kubernetes.io/instance: external-dns
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app.kubernetes.io/name: external-dns
        app.kubernetes.io/instance: external-dns
    spec:
      serviceAccountName: external-dns
      securityContext:
        fsGroup: 65534
      containers:
        - name: external-dns
          securityContext:
            capabilities:
              drop:
              - ALL
            readOnlyRootFilesystem: true
            runAsNonRoot: true
            runAsUser: 65534
          image: registry.k8s.io/external-dns/external-dns:v0.14.0
          imagePullPolicy: IfNotPresent
          args:
            - --log-level=info
            - --log-format=text
            - --interval=1m
            - --source=service
            - --source=ingress
            - --policy=sync # set it upsert-only if you don't want it to delete records
            - --provider=webhook
          ports:
            - name: http
              protocol: TCP
              containerPort: 7979
          livenessProbe:
            failureThreshold: 2
            httpGet:
              path: /healthz
              port: http
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          readinessProbe:
            failureThreshold: 6
            httpGet:
              path: /healthz
              port: http
            initialDelaySeconds: 5
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
        - name: webhook
          securityContext:
            capabilities:
              drop:
                - ALL
            readOnlyRootFilesystem: true
            runAsNonRoot: true
            runAsUser: 65534
          image: ghcr.io/stackitcloud/external-dns-stackit-webhook:v0.2.0
          imagePullPolicy: IfNotPresent
          args:
            - --project-id=c158c736-0300-4044-95c4-b7d404279b35 # your project id
          ports:
            - name: http
              protocol: TCP
              containerPort: 8888
          livenessProbe:
            failureThreshold: 2
            httpGet:
              path: /healthz
              port: http
            initialDelaySeconds: 10
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          readinessProbe:
            failureThreshold: 6
            httpGet:
              path: /healthz
              port: http
            initialDelaySeconds: 5
            periodSeconds: 10
            successThreshold: 1
            timeoutSeconds: 5
          env:
            - name: AUTH_TOKEN
              valueFrom:
                secretKeyRef:
                  name: external-dns-stackit-webhook
                  key: auth-token
EOF

Configuration

The configuration of the STACKIT webhook can be accomplished through command line arguments and environment variables. Below are the options that are available.

--project-id/PROJECT_ID (required): Specifies the project id of the STACKIT project.
--auth-token/AUTH_TOKEN (required if auth-key-path is not set): Defines the authentication token for the STACKIT API. Mutually exclusive with 'auth-key-path'.
--auth-key-path/AUTH_KEY_PATH (required if auth-token is not set): Defines the file path of the service account key for the STACKIT API. Mutually exclusive with 'auth-token'.
--worker/WORKER (optional): Specifies the number of workers to employ for querying the API. Given that we need to iterate over all zones and records, it can be parallelized. However, it is important to avoid setting this number excessively high to prevent receiving 429 rate limiting from the API (default 10).
--base-url/BASE_URL (optional): Identifies the Base URL for utilizing the API ( default "https://dns.api.stackit.cloud").
--api-port/API_PORT (optional): Specifies the port to listen on (default 8888).
--domain-filter/DOMAIN_FILER (optional): Establishes a filter for DNS zone names (default []).
--dry-run/DRY_RUN (optional): Specifies whether to perform a dry run (default false).
--log-level/LOG_LEVEL (optional): Defines the log level (default "info"). Possible values are: debug, info, warn, error.

FAQ

1. Issue with Creating Service using External DNS Annotation

If your zone is example.runs.onstackit.cloud and you're trying to create a service with the following external DNS annotation:

```yaml
apiVersion: v1
kind: Service
metadata:
  annotations:
    external-dns.alpha.kubernetes.io/hostname: example.runs.onstackit.cloud
  labels:
    app.kubernetes.io/name: ingress-nginx
    app.kubernetes.io/instance: nginx
    app.kubernetes.io/part-of: ingress-nginx
    app.kubernetes.io/component: controller
  name: nginx-ingress-controller
  namespace: nginx-ingress-controller
spec:
  type: LoadBalancer
  externalTrafficPolicy: Local
  ipFamilyPolicy: SingleStack
  ipFamilies:
    - IPv4
  ports:
    - name: http
      port: 80
      protocol: TCP
      targetPort: http
    - name: https
      port: 443
      protocol: TCP
      targetPort: https
  selector:
    app.kubernetes.io/component: controller
    app.kubernetes.io/instance: nginx
    app.kubernetes.io/name: ingress-nginx
```

Why isn't it working?

Answer: The External DNS will try to create a TXT record named a-example.runs.onstackit.cloud, which will fail because you can't establish a record outside the zone. The solution is to use a name that's within the zone, such as nginx.example.runs.onstackit.cloud.

2. Issues with Creating Ingresses not in the Zone

For a project containing the zone example.runs.onstackit.cloud, suppose you've created these two ingress:

```yaml
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  annotations:
    ingress.kubernetes.io/rewrite-target: /
    kubernetes.io/ingress.class: nginx
  name: example-ingress-external-dns
  namespace: default
spec:
  rules:
    - host: test.example.runs.onstackit.cloud
      http:
        paths:
          - backend:
              service:
                name: example
                port:
                  number: 80
            path: /
            pathType: Prefix
    - host: test.example.stackit.rocks
      http:
        paths:
          - backend:
              service:
                name: example
                port:
                  number: 80
            path: /
            pathType: Prefix
```

Why isn't it working?

Answer: External DNS will attempt to establish a record set for test.example.stackit.rocks. As the zone example.stackit.rocks isn't within the project, it'll fail. There are two potential fixes:

Incorporate the zone example.stackit.rocks into the project.
Adjust the domain filter to example.runs.onstackit.cloud by setting the domain filter flag --domain-filter="example.runs.onstackit.cloud". This will exclude test.example.stackit.rocks and only generate the record set for test.example.runs.onstackit.cloud.

Development

Run the app:

export BASE_URL="https://dns.api.stackit.cloud"
export PROJECT_ID="c158c736-0300-4044-95c4-b7d404279b35"
export AUTH_TOKEN="your-auth-token"

make run

Lint the code:

make lint

Test the code:

make test