How to automatically renew Azure eventhub

To use JWT to communicate with Azure eventhub we need to renew the JWT credentials
from time to time. This example yaml helps out with that
* Supports both deployment and cronjob based renewal
  * static service principal
  * aad-pod-identity in azure

Signed-off-by: Edvin Norling <edvin.norling@xenit.se>

manifests/integrations/eventhub-credentials-sync/_base/kustomization.yaml

@@ -0,0 +1,27 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+commonLabels:
+  app: credentials-sync-eventhub
+
+resources:
+  - sync.yaml
+
+vars:
+  - name: KUBE_SECRET
+    objref:
+      kind: ConfigMap
+      name: credentials-sync-eventhub
+      apiVersion: v1
+    fieldref:
+      fieldpath: data.KUBE_SECRET
+  - name: ADDRESS
+    objref:
+      kind: ConfigMap
+      name: credentials-sync-eventhub
+      apiVersion: v1
+    fieldref:
+      fieldpath: data.ADDRESS
+
+configurations:
+  - kustomizeconfig.yaml

manifests/integrations/eventhub-credentials-sync/_base/kustomizeconfig.yaml

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+varReference:
+- path: rules/resourceNames
+  kind: Role

manifests/integrations/eventhub-credentials-sync/_base/sync.yaml

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+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: credentials-sync-eventhub
+data:
+  # Patch this ConfigMap with additional values needed for your cloud
+  KUBE_SECRET: webhook-url # does not yet exist -- will be created in the same Namespace
+  ADDRESS: "fluxv2" # the Azure Event Hub name
+  SYNC_PERIOD: "3600" # tokens expire; refresh faster than that
+
+---
+# This Deployment frequently fetches registry tokens and applies them as an imagePullSecret.
+# It's done as a 1-replica Deployment rather than a CronJob, because CronJob scheduling can
+# block cluster bootstraps and cold-reboots from obtaining registry tokens for a considerable time.
+# This deployment will immediately fetch a token, which reduces latency for working image updates.
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+spec:
+  replicas: 1
+  strategy:
+    type: Recreate
+  template:
+    spec:
+      serviceAccountName: credentials-sync-eventhub
+      securityContext:
+        runAsNonRoot: true
+        runAsUser: 1001
+      containers:
+        - image: busybox # override this with a cloud-specific image
+          name: sync
+          envFrom:
+            - configMapRef:
+                name: credentials-sync-eventhub
+          env:
+            - name: RECONCILE_SH # override this env var with a shell function in a kustomize patch
+              value: |-
+                reconcile() {
+                  echo reconciling...
+                }
+          command:
+            - bash
+            - -ceu
+            - |-
+              # template reconcile() into the script
+              # env var is expanded by k8s before the pod starts
+              $(RECONCILE_SH)
+
+              apply-secret() {
+                /kbin/kubectl create secret generic "${1}" \
+                  --from-literal=token="${2}" \
+                  --from-literal=address="${3}" \
+                  --dry-run=client -o=yaml \
+                  | grep -v "creationTimestamp:" \
+                  | /kbin/kubectl apply -f -
+              }
+
+              pause_loop() {
+                sleep "${SYNC_PERIOD:-3600}" || true
+              }
+
+              graceful_exit() {
+                echo "Trapped signal -- $(date)"
+                job_ids="$(
+                  jobs \
+                    | grep "pause_loop" \
+                    | cut -d] -f1 \
+                    | tr [ %
+                  )"
+                # shellcheck disable=SC2086
+                if [ "${job_ids}" ]; then
+                  kill ${job_ids}
+                fi
+                wait
+                echo "Graceful exit -- $(date)"
+              }
+
+              trap graceful_exit INT TERM
+
+              echo "Loop started (period: ${SYNC_PERIOD} s) -- $(date)"
+              while true; do
+                reconcile & wait $!
+                pause_loop & wait $!
+              done
+          resources: {}
+          volumeMounts:
+            - mountPath: /.azure
+              name: cache-volume
+      volumes:
+        - emptyDir: {}
+          name: cache-volume
+
+# RBAC necessary for our Deployment to apply our secret that will store the JWT token
+---
+kind: Role
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+rules:
+  - apiGroups: [""]
+    resources:
+      - secrets
+    verbs:
+      - get
+      - create
+      - update
+      - patch
+    # # Lock this down to the specific Secret name  (Optional)
+    #resourceNames:
+    #  - $(KUBE_SECRET) # templated from kustomize vars referencing ConfigMap, also see kustomizeconfig.yaml
+---
+kind: RoleBinding
+apiVersion: rbac.authorization.k8s.io/v1
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+subjects:
+  - kind: ServiceAccount
+    name: credentials-sync-eventhub
+roleRef:
+  kind: Role
+  name: credentials-sync-eventhub
+  apiGroup: rbac.authorization.k8s.io
+---
+apiVersion: v1
+kind: ServiceAccount
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system