whitelist_regions.json

{
  "type": "Microsoft.Authorization/policyDefinitions",
  "name": "whitelist_regions",
  "properties": {
    "metadata": {
      "category": "General"
    },
    "parameters": {
      "listOfRegionsAllowed": {
        "type": "Array",
        "metadata": {
          "description": "The list of regions where resources can be deployed.",
          "displayName": "Allowed regions",
          "strongType": "location"
        },
        "defaultValue": [
          "UK South",
          "UK West"
        ]
      },
      "effect": {
        "type": "String",
        "defaultValue": "Audit",
        "allowedValues": [
          "Audit",
          "Deny",
          "Disabled"
        ],
        "metadata": {
          "displayName": "Effect",
          "description": "The effect determines what happens when the policy rule is evaluated to match"
        }
      }
    },
    "policyRule": {
      "if": {
        "not": {
          "field": "location",
          "in": "[parameters('listOfRegionsAllowed')]"
        }
      },
      "then": {
        "effect": "[parameters('effect')]"
      }
    }
  }
}