Configure plugins by name

To configure core plugin or service plugins, instead of using class names,
simpler names can also be used, ex:

service_plugins = router, firewall, lbaas

For compatibility with previous versions, the class name of a plugin can be
specified instead of its entrypoint name, ex:

service_plugins = router, neutron.services.firewall.fwaas_plugin.FirewallPlugin, lbaas

DocImpact

Implements: blueprint config-plugin-by-name
Change-Id: Ia4aaa1d305b160a4d6dab9e227c744727a4c78c2

neutron/manager.py

@@ -25,6 +25,8 @@ from neutron.openstack.common import log as logging
 from neutron.openstack.common import periodic_task
 from neutron.plugins.common import constants
 
+from stevedore import driver
+
 
 LOG = logging.getLogger(__name__)
 
@@ -108,16 +110,10 @@ class NeutronManager(object):
         #                intentianally to allow v2 plugins to be monitored
         #                for performance metrics.
         plugin_provider = cfg.CONF.core_plugin
-        LOG.debug(_("Plugin location: %s"), plugin_provider)
-        # If the plugin can't be found let them know gracefully
-        try:
-            LOG.info(_("Loading Plugin: %s"), plugin_provider)
-            plugin_klass = importutils.import_class(plugin_provider)
-        except ImportError:
-            LOG.exception(_("Error loading plugin"))
-            raise Exception(_("Plugin not found. "))
+        LOG.info(_("Loading core plugin: %s"), plugin_provider)
+        self.plugin = self._get_plugin_instance('neutron.core_plugins',
+                                                plugin_provider)
         legacy.modernize_quantum_config(cfg.CONF)
-        self.plugin = plugin_klass()
 
         msg = validate_post_plugin_load()
         if msg:
@@ -131,6 +127,21 @@ class NeutronManager(object):
         self.service_plugins = {constants.CORE: self.plugin}
         self._load_service_plugins()
 
+    def _get_plugin_instance(self, namespace, plugin_provider):
+        try:
+            # Try to resolve plugin by name
+            mgr = driver.DriverManager(namespace, plugin_provider)
+            plugin_class = mgr.driver
+        except RuntimeError as e1:
+            # fallback to class name
+            try:
+                plugin_class = importutils.import_class(plugin_provider)
+            except ImportError as e2:
+                LOG.exception(_("Error loading plugin by name, %s"), e1)
+                LOG.exception(_("Error loading plugin by class, %s"), e2)
+                raise ImportError(_("Plugin not found."))
+        return plugin_class()
+
     def _load_services_from_core_plugin(self):
         """Puts core plugin in service_plugins for supported services."""
         LOG.debug(_("Loading services supported by the core plugin"))
@@ -159,13 +170,10 @@ class NeutronManager(object):
         for provider in plugin_providers:
             if provider == '':
                 continue
-            try:
-                LOG.info(_("Loading Plugin: %s"), provider)
-                plugin_class = importutils.import_class(provider)
-            except ImportError:
-                LOG.exception(_("Error loading plugin"))
-                raise ImportError(_("Plugin not found."))
-            plugin_inst = plugin_class()
+
+            LOG.info(_("Loading Plugin: %s"), provider)
+            plugin_inst = self._get_plugin_instance('neutron.service_plugins',
+                                                    provider)
 
             # only one implementation of svc_type allowed
             # specifying more than one plugin