Deny-Subnet-Without-Nsg.json

{
  "name": "Deny-Subnet-Without-Nsg",
  "type": "Microsoft.Authorization/policyDefinitions",
  "apiVersion": "2021-06-01",
  "scope": null,
  "properties": {
    "policyType": "Custom",
    "mode": "All",
    "displayName": "Subnets should have a Network Security Group",
    "description": "This policy denies the creation of a subnet without a Network Security Group. NSG help to protect traffic across subnet-level.",
    "metadata": {
      "version": "2.0.0",
      "category": "Network",
      "source": "https://github.com/Azure/Enterprise-Scale/",
      "alzCloudEnvironments": [
        "AzureCloud",
        "AzureChinaCloud",
        "AzureUSGovernment"
      ]
    },
    "parameters": {
      "effect": {
        "type": "String",
        "allowedValues": [
          "Audit",
          "Deny",
          "Disabled"
        ],
        "defaultValue": "Deny",
        "metadata": {
          "displayName": "Effect",
          "description": "Enable or disable the execution of the policy"
        }
      },
      "excludedSubnets": {
        "type": "Array",
        "metadata": {
          "displayName": "Excluded Subnets",
          "description": "Array of subnet names that are excluded from this policy"
        },
        "defaultValue": [
          "GatewaySubnet",
          "AzureFirewallSubnet",
          "AzureFirewallManagementSubnet"
        ]
      }
    },
    "policyRule": {
      "if": {
        "anyOf": [
          {
            "allOf": [
              {
                "equals": "Microsoft.Network/virtualNetworks",
                "field": "type"
              },
              {
                "count": {
                  "field": "Microsoft.Network/virtualNetworks/subnets[*]",
                  "where": {
                    "allOf": [
                      {
                        "exists": "false",
                        "field": "Microsoft.Network/virtualNetworks/subnets[*].networkSecurityGroup.id"
                      },
                      {
                        "field": "Microsoft.Network/virtualNetworks/subnets[*].name",
                        "notIn": "[[parameters('excludedSubnets')]"
                      }
                    ]
                  }
                },
                "notEquals": 0
              }
            ]
          },
          {
            "allOf": [
              {
                "field": "type",
                "equals": "Microsoft.Network/virtualNetworks/subnets"
              },
              {
                "field": "name",
                "notIn": "[[parameters('excludedSubnets')]"
              },
              {
                "field": "Microsoft.Network/virtualNetworks/subnets/networkSecurityGroup.id",
                "exists": "false"
              }
            ]
          }
        ]
      },
      "then": {
        "effect": "[[parameters('effect')]"
      }
    }
  }
}