Prevent Duplicate HorizontalPodAutoscalers

apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: prevent-duplicate-hpa
  annotations:
    policies.kyverno.io/title: Prevent Duplicate HorizontalPodAutoscalers
    policies.kyverno.io/category: Other
    policies.kyverno.io/severity: medium
    kyverno.io/kyverno-version: 1.11.4
    kyverno.io/kubernetes-version: "1.27"
    policies.kyverno.io/subject: HorizontalPodAutoscaler
    policies.kyverno.io/description: HorizontalPodAutoscaler (HPA) is useful to automatically adjust the number of pods in a deployment or replication controller. It requires defining a specific target resource by kind and name. There are no built-in validation checks by the HPA controller to prevent the creation of multiple HPAs which target the same resource. This policy has two rules, the first of which ensures that the only targetRef kinds accepted are one of either Deployment, StatefulSet, ReplicaSet, or DaemonSet. The second prevents the creation of duplicate HPAs by validating that any new HPA targets a unique resource.
spec:
  validationFailureAction: Audit
  background: false
  rules:
    - name: verify-kind-name-duplicates
      match:
        any:
          - resources:
              kinds:
                - HorizontalPodAutoscaler
              operations:
                - CREATE
      validate:
        message: "The target kind must be specified exactly as Deployment, StatefulSet, ReplicaSet, or DaemonSet.        "
        pattern:
          spec:
            scaleTargetRef:
              kind: Deployment | StatefulSet | ReplicaSet | DaemonSet
    - name: check-targetref-duplicates
      match:
        any:
          - resources:
              kinds:
                - HorizontalPodAutoscaler
              operations:
                - CREATE
      preconditions:
        all:
          - key:
              - Deployment
              - StatefulSet
              - ReplicaSet
              - DaemonSet
            operator: AnyIn
            value: "{{ request.object.spec.scaleTargetRef.kind }}"
      context:
        - name: targets
          apiCall:
            urlPath: /apis/autoscaling/v1/namespaces/{{ request.namespace }}/horizontalpodautoscalers
            jmesPath: items[?spec.scaleTargetRef.kind=='{{ request.object.spec.scaleTargetRef.kind }}'].spec.scaleTargetRef.name
      validate:
        message: "The target {{ request.object.spec.scaleTargetRef.kind }} named {{ request.object.spec.scaleTargetRef.name }} already has an existing HPA configured for it. Duplicate HPAs are not allowed.        "
        deny:
          conditions:
            all:
              - key: "{{ request.object.spec.scaleTargetRef.name }}"
                operator: AnyIn
                value: "{{ targets }}"