Use Stevedore for better extensions

Since all Oslo library drivers are discoverable via
stevedore, we should use stevedore in Castellan as well.
This will make it easier for folks to write their own
custom drivers. Stevedore uses setuptools entry points
for implementing the common patterns for dynamically
loading extensions.

We add [key_manager]/backend as the new option to set
the custom driver. For a while, we should support the
older values that used to be specified using
[key_manager]/apiclass.

Change-Id: I2610459839806a5591da1efa314dfa52bcfb7cda

castellan/key_manager/__init__.py

@@ -13,13 +13,21 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 from oslo_config import cfg
+from oslo_log import log as logging
 from oslo_utils import importutils
+from stevedore import driver
+from stevedore import exception
+
+LOG = logging.getLogger(__name__)
 
 key_manager_opts = [
-    cfg.StrOpt('api_class',
+    cfg.StrOpt('backend',
-               default='castellan.key_manager.barbican_key_manager'
+               default='barbican',
-                       '.BarbicanKeyManager',
+               deprecated_name='api_class',
-               help='The full class name of the key manager API class'),
+               deprecated_group='key_manager',
+               help='Specify the key manager implementation. Default is '
+                    '"barbican".Will support the  values earlier set using '
+                    '[key_manager]/api_class for some time.'),
 ]
 
 
@@ -27,5 +35,14 @@ def API(configuration=None):
     conf = configuration or cfg.CONF
     conf.register_opts(key_manager_opts, group='key_manager')
 
-    cls = importutils.import_class(conf.key_manager.api_class)
+    try:
-    return cls(configuration=conf)
+        mgr = driver.DriverManager("castellan.drivers",
+                                   conf.key_manager.backend,
+                                   invoke_on_load=True,
+                                   invoke_args=[conf])
+        return mgr.driver
+    except exception.NoMatches:
+        LOG.warning("Deprecation Warning : %s is not a stevedore based driver,"
+                    " trying to load it as a class", conf.key_manager.backend)
+        cls = importutils.import_class(conf.key_manager.backend)
+        return cls(configuration=conf)

castellan/options.py

@@ -30,9 +30,10 @@ _DEFAULT_LOGGING_CONTEXT_FORMAT = ('%(asctime)s.%(msecs)03d %(process)d '
                                    '%(message)s')
 
 
-def set_defaults(conf, api_class=None, barbican_endpoint=None,
+def set_defaults(conf, backend=None, barbican_endpoint=None,
                  barbican_api_version=None, auth_endpoint=None,
-                 retry_delay=None, number_of_retries=None, verify_ssl=None):
+                 retry_delay=None, number_of_retries=None, verify_ssl=None,
+                 api_class=None):
     """Set defaults for configuration values.
 
     Overrides the default options values.
@@ -49,8 +50,10 @@ def set_defaults(conf, api_class=None, barbican_endpoint=None,
     if bkm:
         conf.register_opts(bkm.barbican_opts, group=bkm.BARBICAN_OPT_GROUP)
 
-    if api_class is not None:
+    # Use the new backend option if set or fall back to the older api_class
-        conf.set_default('api_class', api_class, group='key_manager')
+    default_backend = backend or api_class
+    if default_backend is not None:
+        conf.set_default('backend', default_backend, group='key_manager')
 
     if bkm is not None:
         if barbican_endpoint is not None:

castellan/tests/unit/key_manager/test_barbican_key_manager.py

@@ -20,7 +20,6 @@ import calendar
 
 from barbicanclient import exceptions as barbican_exceptions
 import mock
-from oslo_config import cfg
 from oslo_utils import timeutils
 
 from castellan.common import exception
@@ -32,7 +31,7 @@ from castellan.tests.unit.key_manager import test_key_manager
 class BarbicanKeyManagerTestCase(test_key_manager.KeyManagerTestCase):
 
     def _create_key_manager(self):
-        return barbican_key_manager.BarbicanKeyManager(cfg.CONF)
+        return barbican_key_manager.BarbicanKeyManager(self.conf)
 
     def setUp(self):
         super(BarbicanKeyManagerTestCase, self).setUp()

castellan/tests/unit/key_manager/test_key_manager.py

@@ -17,8 +17,15 @@
 Test cases for the key manager.
 """
 
+from oslo_config import cfg
+from oslo_config import fixture
+
+from castellan import key_manager
+from castellan.key_manager import barbican_key_manager
 from castellan.tests import base
 
+CONF = cfg.CONF
+
 
 class KeyManagerTestCase(base.TestCase):
 
@@ -28,4 +35,18 @@ class KeyManagerTestCase(base.TestCase):
     def setUp(self):
         super(KeyManagerTestCase, self).setUp()
 
+        self.conf = self.useFixture(fixture.Config()).conf
+
         self.key_mgr = self._create_key_manager()
+
+
+class DefaultKeyManagerImplTestCase(KeyManagerTestCase):
+
+    def _create_key_manager(self):
+        return key_manager.API(self.conf)
+
+    def test_default_key_manager(self):
+        self.assertEqual("barbican", self.conf.key_manager.backend)
+        self.assertIsNotNone(self.key_mgr)
+        self.assertIsInstance(self.key_mgr,
+                              barbican_key_manager.BarbicanKeyManager)

castellan/tests/unit/test_options.py

@@ -15,9 +15,11 @@
 
 from oslo_config import cfg
 
+from castellan import key_manager
 from castellan.key_manager import barbican_key_manager as bkm
 from castellan import options
 from castellan.tests import base
+from castellan.tests.unit.key_manager import mock_key_manager
 
 
 class TestOptions(base.TestCase):
@@ -25,9 +27,15 @@ class TestOptions(base.TestCase):
     def test_set_defaults(self):
         conf = cfg.ConfigOpts()
 
-        api_class = 'test.api.class'
+        self.assertTrue(isinstance(key_manager.API(conf),
-        options.set_defaults(conf, api_class=api_class)
+                                   bkm.BarbicanKeyManager))
-        self.assertEqual(api_class, conf.key_manager.api_class)
+
+        cls = mock_key_manager.MockKeyManager
+        backend = '%s.%s' % (cls.__module__, cls.__name__)
+        options.set_defaults(conf, backend=backend)
+        self.assertEqual(backend, conf.key_manager.backend)
+        self.assertIsInstance(key_manager.API(conf),
+                              mock_key_manager.MockKeyManager)
 
         barbican_endpoint = 'http://test-server.org:9311/'
         options.set_defaults(conf, barbican_endpoint=barbican_endpoint)

requirements.txt

@@ -11,4 +11,5 @@ oslo.context>=2.14.0 # Apache-2.0
 oslo.i18n!=3.15.2,>=2.1.0 # Apache-2.0
 oslo.log>=3.22.0 # Apache-2.0
 oslo.utils>=3.20.0 # Apache-2.0
+stevedore>=1.20.0 # Apache-2.0
 keystoneauth1>=3.1.0 # Apache-2.0

setup.cfg

@@ -27,6 +27,9 @@ oslo.config.opts =
     castellan.tests.functional.config = castellan.tests.functional.config:list_opts
     castellan.config = castellan.options:list_opts
 
+castellan.drivers =
+    barbican = castellan.key_manager.barbican_key_manager:BarbicanKeyManager
+
 [build_sphinx]
 source-dir = doc/source
 build-dir = doc/build