policyDefinitions/Kubernetes/allowed-volume-types/template.yaml

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8sazurevolumetypes
spec:
  crd:
    spec:
      names:
        kind: K8sAzureVolumeTypes
      validation:
        # Schema for the `parameters` field
        openAPIV3Schema:
          properties:
            volumes:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8sazurevolumetypes

        violation[{"msg": msg, "details": {}}] {
            volume_fields := {x | input.review.object.spec.volumes[_][x]; x != "name"}
            field := volume_fields[_]
            not input_volume_type_allowed(field)
            msg := sprintf("The volume type %v is not allowed, pod: %v. Allowed volume types: %v", [field, input.review.object.metadata.name, input.parameters.volumes])
        }

        # * may be used to allow all volume types
        input_volume_type_allowed(field) {
            input.parameters.volumes[_] == "*"
        }

        input_volume_type_allowed(field) {
            field == input.parameters.volumes[_]
        }