feat(terraform): Ensure ephemeral disks are used for OS disks (#5584)

Created check

Co-authored-by: Thomas Defise <[email protected]>

checkov/terraform/checks/resource/azure/AKSEphemeralOSDisks.py

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+from checkov.common.models.enums import CheckCategories
+from checkov.terraform.checks.resource.base_resource_value_check import BaseResourceValueCheck
+from typing import Any
+
+
+class AKSEphemeralOSDisks(BaseResourceValueCheck):
+    def __init__(self) -> None:
+        """
+        Temporary data can contain sensitive data at some points, by using ephemeral disks,
+        we ensure that data written to OS disk is stored on local VM storage and isn't persisted to Azure Storage
+
+        Azure automatically replicates data stored in the managed OS disk of a virtual machine to Azure storage
+        to avoid data loss in case the virtual machine needs to be relocated to another host.
+        Generally speaking, containers are not designed to have local state persisted to the managed OS disk,
+        hence this behavior offers limited value to AKS hosted while providing some drawbacks,
+        including slower node provisioning and higher read/write latency.
+
+        Ephemeral disks allow us also to have faster cluster operations like scale or upgrade
+        due to faster re-imaging and boot times.
+        """
+        name = "Ensure ephemeral disks are used for OS disks"
+        id = "CKV_AZURE_226"
+        supported_resources = ("azurerm_kubernetes_cluster",)
+        categories = (CheckCategories.KUBERNETES,)
+        super().__init__(name=name, id=id, categories=categories, supported_resources=supported_resources)
+
+    def get_inspected_key(self) -> str:
+        return "os_disk_type"
+
+    def get_expected_value(self) -> Any:
+        return "Ephemeral"
+
+
+check = AKSEphemeralOSDisks()

tests/terraform/checks/resource/azure/example_AKSEphemeralOSDisks/main.tf

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+resource "azurerm_kubernetes_cluster" "pass" {
+  name                  = "internal"
+  kubernetes_cluster_id = azurerm_kubernetes_cluster.example.id
+  vm_size               = "Standard_DS2_v2"
+  node_count            = 1
+  os_disk_type          = "Ephemeral"
+
+  tags = {
+    Environment = "Production"
+  }
+}
+
+resource "azurerm_kubernetes_cluster" "fail" {
+  name                  = "internal"
+  kubernetes_cluster_id = azurerm_kubernetes_cluster.example.id
+  vm_size               = "Standard_DS2_v2"
+  node_count            = 1
+
+  tags = {
+    Environment = "Production"
+  }
+}
+
+resource "azurerm_kubernetes_cluster" "fail2" {
+  name                  = "internal"
+  kubernetes_cluster_id = azurerm_kubernetes_cluster.example.id
+  vm_size               = "Standard_DS2_v2"
+  node_count            = 1
+  os_disk_type          = "Managed"
+
+  tags = {
+    Environment = "Production"
+  }
+}

tests/terraform/checks/resource/azure/test_AKSEphemeralOSDisks.py

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+import os
+import unittest
+
+from checkov.runner_filter import RunnerFilter
+from checkov.terraform.runner import Runner
+from checkov.terraform.checks.resource.azure.AKSEphemeralOSDisks import check
+
+
+class AKSEphemeralOSDisks(unittest.TestCase):
+
+    def test(self):
+        runner = Runner()
+        current_dir = os.path.dirname(os.path.realpath(__file__))
+
+        test_files_dir = os.path.join(current_dir, "example_AKSEphemeralOSDisks")
+        report = runner.run(root_folder=test_files_dir,
+                            runner_filter=RunnerFilter(checks=[check.id]))
+        summary = report.get_summary()
+
+        passing_resources = {
+            'azurerm_kubernetes_cluster.pass',
+        }
+        failing_resources = {
+            'azurerm_kubernetes_cluster.fail',
+            'azurerm_kubernetes_cluster.fail2',
+        }
+        skipped_resources = {}
+
+        passed_check_resources = set([c.resource for c in report.passed_checks])
+        failed_check_resources = set([c.resource for c in report.failed_checks])
+
+        self.assertEqual(summary['passed'], len(passing_resources))
+        self.assertEqual(summary['failed'], len(failing_resources))
+        self.assertEqual(summary['skipped'], len(skipped_resources))
+        self.assertEqual(summary['parsing_errors'], 0)
+
+        self.assertEqual(passing_resources, passed_check_resources)
+        self.assertEqual(failing_resources, failed_check_resources)
+
+
+if __name__ == '__main__':
+    unittest.main()