Allow disabling instance image cache

We document that this can be disabled by setting the
instance_master_path config  to "<None>",
but don't actually support it in code. oslo.config doesn't actually
translate that value to the Python None as we expect.

Allow disabling the cache by setting the config to the empty string, as
in "instance_master_path=". This doesn't make sense as a directory to
use as a cache anyway, so it shouldn't break anyone.

Change-Id: I1bb62d55e3e18272fd5da355d63fd2c11a033acd
Story: 2004279
Task: 27829

ironic/conf/pxe.py

@@ -36,7 +36,7 @@ opts = [
                default='/var/lib/ironic/master_images',
                help=_('On the ironic-conductor node, directory where master '
                       'instance images are stored on disk. '
-                      'Setting to <None> disables image caching.')),
+                      'Setting to the empty string disables image caching.')),
     cfg.IntOpt('image_cache_size',
                default=20480,
                help=_('Maximum size (in MiB) of cache for master images, '

ironic/drivers/modules/deploy_utils.py

@@ -1113,8 +1113,9 @@ def direct_deploy_should_convert_raw_image(node):
 class InstanceImageCache(image_cache.ImageCache):
 
     def __init__(self):
+        master_path = CONF.pxe.instance_master_path or None
         super(self.__class__, self).__init__(
-            CONF.pxe.instance_master_path,
+            master_path,
             # MiB -> B
             cache_size=CONF.pxe.image_cache_size * 1024 * 1024,
             # min -> sec

ironic/tests/unit/drivers/modules/test_deploy_utils.py

@@ -2761,3 +2761,29 @@ class TestStorageInterfaceUtils(db_base.DbTestCase):
         with task_manager.acquire(
                 self.context, self.node.uuid, shared=False) as task:
             self.assertFalse(utils.is_iscsi_boot(task))
+
+
+class InstanceImageCacheTestCase(db_base.DbTestCase):
+    @mock.patch.object(fileutils, 'ensure_tree')
+    def test_with_master_path(self, mock_ensure_tree):
+        self.config(instance_master_path='/fake/path', group='pxe')
+        self.config(image_cache_size=500, group='pxe')
+        self.config(image_cache_ttl=30, group='pxe')
+
+        cache = utils.InstanceImageCache()
+
+        mock_ensure_tree.assert_called_once_with('/fake/path')
+        self.assertEqual(500 * 1024 * 1024, cache._cache_size)
+        self.assertEqual(30 * 60, cache._cache_ttl)
+
+    @mock.patch.object(fileutils, 'ensure_tree')
+    def test_without_master_path(self, mock_ensure_tree):
+        self.config(instance_master_path='', group='pxe')
+        self.config(image_cache_size=500, group='pxe')
+        self.config(image_cache_ttl=30, group='pxe')
+
+        cache = utils.InstanceImageCache()
+
+        mock_ensure_tree.assert_not_called()
+        self.assertEqual(500 * 1024 * 1024, cache._cache_size)
+        self.assertEqual(30 * 60, cache._cache_ttl)

releasenotes/notes/fix-instance-master-path-config-fa524c907a7888e5.yaml

@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Fixes an issue where the master instance image cache could not be disabled.
+    The configuration option ``[pxe]/instance_master_path`` may now be set to
+    the empty string to disable the cache.