policyDefinitions/Kubernetes/flexvolume-drivers/template.yaml

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: k8sazureflexvolumes
spec:
  crd:
    spec:
      names:
        kind: K8sAzureFlexVolumes
      validation:
        # Schema for the `parameters` field
        openAPIV3Schema:
          properties:
            allowedFlexVolumeDrivers:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8sazureflexvolumes

        violation[{"msg": msg, "details": {}}] {
            volume := input_flexvolumes[_]
            not input_flexvolumes_allowed(volume)
            msg := sprintf("FlexVolume %v is not allowed, pod: %v. Allowed drivers: %v", [volume, input.review.object.metadata.name, input.parameters.allowedFlexVolumeDrivers])
        }

        input_flexvolumes_allowed(volume) {
            input.parameters.allowedFlexVolumeDrivers[_] == volume.flexVolume.driver
        }

        input_flexvolumes[v] {
            v := input.review.object.spec.volumes[_]
            has_field(v, "flexVolume")
        }

        # has_field returns whether an object has a field
        has_field(object, field) = true {
            object[field]
        }