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/_cronjobs/azure/az-identity.yaml

@@ -0,0 +1,16 @@
+# This is a stub resource patched by config-patches.yaml, so that all config is visible in one file
+---
+apiVersion: aadpodidentity.k8s.io/v1
+kind: AzureIdentity
+metadata:
+  name: lab # if this is changed, also change in config-patches.yaml
+  namespace: flux-system
+---
+apiVersion: aadpodidentity.k8s.io/v1
+kind: AzureIdentityBinding
+metadata:
+  name: lab
+  namespace: flux-system
+spec:
+  azureIdentity: lab
+  selector: lab

manifests/integrations/eventhub-credentials-sync/_cronjobs/azure/config-patches.yaml

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+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: credentials-sync-eventhub
+data:
+  KUBE_SECRET: webhook-url # does not yet exist -- will be created in the same Namespace
+  ADDRESS: "fluxv2" # the Azure Event Hub name
+
+# Create an identity in Azure and assign it a role to write to Azure Event Hub (note: the identity's resourceGroup should match the Azure Event Hub):
+#     az identity create -n eventhub-write
+#     az role assignment create --role eventhub --assignee-object-id "$(az identity show -n eventhub-write -o tsv --query principalId)"
+# Fetch the clientID and resourceID to configure the AzureIdentity spec below:
+#     az identity show -n eventhub-write -otsv --query clientId
+#     az identity show -n eventhub-write -otsv --query resourceId
+---
+apiVersion: aadpodidentity.k8s.io/v1
+kind: AzureIdentity
+metadata:
+  name: lab
+  namespace: flux-system
+spec:
+  clientID: 82d01fb0-7799-4d9d-92c7-21e7632c0000
+  resourceID: /subscriptions/82d01fb0-7799-4d9d-92c7-21e7632c0000/resourceGroups/stealthybox/providers/Microsoft.ManagedIdentity/userAssignedIdentities/eventhub-write
+  type: 0
+---
+apiVersion: aadpodidentity.k8s.io/v1
+kind: AzureIdentityBinding
+metadata:
+  name: lab
+  namespace: flux-system
+spec:
+  azureIdentity: jwt-lab
+  selector: jwt-lab
+
+# Set the reconcile period + specify the pod-identity via the aadpodidbinding label
+---
+apiVersion: batch/v1beta1
+kind: CronJob
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+spec:
+  schedule: 0 * * * * # JWT tokens expire every 24 hours; refresh faster than that
+  jobTemplate:
+    spec:
+      template:
+        metadata:
+          labels:
+            aadpodidbinding: $(AZ_IDENTITY_NAME) # match the AzureIdentity name

manifests/integrations/eventhub-credentials-sync/_cronjobs/azure/kubectl-patch.yaml

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+apiVersion: batch/v1beta1
+kind: CronJob
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+spec:
+  jobTemplate:
+    spec:
+      template:
+        spec:
+          initContainers:
+            - image: bitnami/kubectl
+              securityContext:
+                privileged: false
+                readOnlyRootFilesystem: true
+                allowPrivilegeEscalation: false
+              name: copy-kubectl
+              # it's okay to do this because kubectl is a statically linked binary
+              command:
+                - sh
+                - -ceu
+                - cp $(which kubectl) /kbin/
+              resources: {}
+              volumeMounts:
+                - name: kbin
+                  mountPath: /kbin
+          containers:
+            - name: sync
+              volumeMounts:
+                - name: kbin
+                  mountPath: /kbin
+          volumes:
+            - name: kbin
+              emptyDir: {}

manifests/integrations/eventhub-credentials-sync/_cronjobs/azure/kustomization.yaml

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+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+
+namePrefix: jwt-
+commonLabels:
+  app: jwt-eventhub-credentials-sync
+
+namespace: flux-system
+
+bases:
+  - ../_base
+resources:
+  - az-identity.yaml
+
+patchesStrategicMerge:
+  - config-patches.yaml
+  - kubectl-patch.yaml
+  - reconcile-patch.yaml
+
+vars:
+  - name: AZ_IDENTITY_NAME
+    objref:
+      kind: AzureIdentity
+      name: lab
+      apiVersion: aadpodidentity.k8s.io/v1
+
+configurations:
+  - kustomizeconfig.yaml

manifests/integrations/eventhub-credentials-sync/_cronjobs/azure/kustomizeconfig.yaml

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+varReference:
+  - path: spec/jobTemplate/spec/template/metadata/labels
+    kind: CronJob

manifests/integrations/eventhub-credentials-sync/_cronjobs/azure/reconcile-patch.yaml

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+apiVersion: batch/v1beta1
+kind: CronJob
+metadata:
+  name: credentials-sync-eventhub
+  namespace: flux-system
+spec:
+  jobTemplate:
+    spec:
+      template:
+        spec:
+          containers:
+            - name: sync
+              image: mcr.microsoft.com/azure-cli
+              env:
+                - name: RECONCILE_SH
+                  value: |-
+                    reconcile() {
+                      echo "Starting JWT token sync -- $(date)"
+                      echo "Logging into Azure"
+                      az login --identity
+                      echo "Getting JWT token"
+                      token=$(az account get-access-token --resource https://eventhubs.azure.net |jq -r .accessToken)
+                      echo "Creating secret: ${KUBE_SECRET}"
+                      apply-secret "${KUBE_SECRET}" ${token} "${ADDRESS}"
+                      echo "Finished JWT token sync -- $(date)"
+                      echo
+                    }