Add a common generic dynamic loader for watcher

In watcher, an audit generates a set of actions which
aims at achieving a given goal (lower energy consumption, ...).
It is possible to configure different strategies in order to achieve
each goal. Each strategy is written as a Python class which produces
a set of actions. Today, the set of possible actions is fixed for a
given version of Watcher and enables optimization algorithms to
include actions such as instance migration, changing hypervisor state,
changing power state (ACPI level, ...).

This patchset add a common generic dynamic loader for plugins,
such as for custom Actions, Strategies, Planners, etc.

Partially implements: blueprint watcher-add-actions-via-conf

Change-Id: I59d031b93865fff2540e3973921e1bdafa95f88e

watcher/decision_engine/strategy/loading/base.py

@@ -1,49 +0,0 @@
-# -*- encoding: utf-8 -*-
-# Copyright (c) 2015 b<>com
-#
-# Authors: Jean-Emile DARTOIS <jean-emile.dartois@b-com.com>
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-# http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
-# implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-#
-import abc
-from oslo_log import log
-import six
-
-from watcher.decision_engine.strategy.strategies.dummy_strategy import \
-    DummyStrategy
-
-LOG = log.getLogger(__name__)
-
-
-@six.add_metaclass(abc.ABCMeta)
-class BaseStrategyLoader(object):
-    default_strategy_cls = DummyStrategy
-
-    @abc.abstractmethod
-    def load_available_strategies(self):
-        raise NotImplementedError()
-
-    def load(self, strategy_to_load=None):
-        strategy_selected = None
-        try:
-            available_strategies = self.load_available_strategies()
-            LOG.debug("Available strategies: %s ", available_strategies)
-            strategy_cls = available_strategies.get(
-                strategy_to_load, self.default_strategy_cls
-            )
-            strategy_selected = strategy_cls()
-        except Exception as exc:
-            LOG.exception(exc)
-
-        return strategy_selected

watcher/decision_engine/strategy/loading/default.py

@@ -20,19 +20,13 @@
 from __future__ import unicode_literals
 
 from oslo_log import log
-from stevedore import ExtensionManager
-
-from watcher.decision_engine.strategy.loading.base import BaseStrategyLoader
 
+from watcher.common.loader.default import DefaultLoader
 
 LOG = log.getLogger(__name__)
 
 
-class DefaultStrategyLoader(BaseStrategyLoader):
-
-    def load_available_strategies(self):
-        extension_manager = ExtensionManager(
-            namespace='watcher_strategies',
-            invoke_on_load=False,
-        )
-        return {ext.name: ext.plugin for ext in extension_manager.extensions}
+class DefaultStrategyLoader(DefaultLoader):
+    def __init__(self):
+        super(DefaultStrategyLoader, self).__init__(
+            namespace='watcher_strategies')