Use taskflow library for building and executing action plans

The aim of this patchset is to integrate taskflow in
the Watcher Applier. Taskflow will help us a lot to make
Action Plan execution easy, consistent, scalable and reliable.

DocImpact

Partially implements: blueprint use-taskflow

Change-Id: I903d6509d74a61ad64e1506b8a7156e6e91abcfb
Closes-Bug: #1535326
Closes-Bug: #1531912

watcher/applier/workflow_engine/default.py

@@ -0,0 +1,159 @@
+# -*- encoding: utf-8 -*-
+# Copyright (c) 2016 b<>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.
+#
+
+from oslo_log import log
+from taskflow import engines
+from taskflow.patterns import graph_flow as gf
+from taskflow import task
+
+from watcher._i18n import _LE, _LW, _LC
+from watcher.applier.workflow_engine import base
+from watcher.objects import action as obj_action
+
+LOG = log.getLogger(__name__)
+
+
+class DefaultWorkFlowEngine(base.BaseWorkFlowEngine):
+    def decider(self, history):
+        # FIXME(jed) not possible with the current Watcher Planner
+        #
+        # decider – A callback function that will be expected to
+        # decide at runtime whether v should be allowed to execute
+        # (or whether the execution of v should be ignored,
+        # and therefore not executed). It is expected to take as single
+        # keyword argument history which will be the execution results of
+        # all u decideable links that have v as a target. It is expected
+        # to return a single boolean
+        # (True to allow v execution or False to not).
+        return True
+
+    def execute(self, actions):
+        try:
+            # NOTE(jed) We want to have a strong separation of concern
+            # between the Watcher planner and the Watcher Applier in order
+            # to us the possibility to support several workflow engine.
+            # We want to provide the 'taskflow' engine by
+            # default although we still want to leave the possibility for
+            # the users to change it.
+            # todo(jed) we need to change the way the actions are stored.
+            # The current implementation only use a linked list of actions.
+            # todo(jed) add olso conf for retry and name
+            flow = gf.Flow("watcher_flow")
+            previous = None
+            for a in actions:
+                task = TaskFlowActionContainer(a, self)
+                flow.add(task)
+                if previous is None:
+                    previous = task
+                    # we have only one Action in the Action Plan
+                    if len(actions) == 1:
+                        nop = TaskFlowNop()
+                        flow.add(nop)
+                        flow.link(previous, nop)
+                else:
+                    # decider == guard (UML)
+                    flow.link(previous, task, decider=self.decider)
+                    previous = task
+
+            e = engines.load(flow)
+            e.run()
+            return True
+        except Exception as e:
+            LOG.exception(e)
+            return False
+
+
+class TaskFlowActionContainer(task.Task):
+    def __init__(self, db_action, engine):
+        name = "action_type:{0} uuid:{1}".format(db_action.action_type,
+                                                 db_action.uuid)
+        super(TaskFlowActionContainer, self).__init__(name=name)
+        self._db_action = db_action
+        self._engine = engine
+        self.loaded_action = None
+
+    @property
+    def action(self):
+        if self.loaded_action is None:
+            action = self.engine.action_factory.make_action(self._db_action)
+            self.loaded_action = action
+        return self.loaded_action
+
+    @property
+    def engine(self):
+        return self._engine
+
+    def pre_execute(self):
+        try:
+            self.engine.notify(self._db_action,
+                               obj_action.Status.ONGOING)
+            LOG.debug("Precondition action %s", self.name)
+            self.action.precondition()
+        except Exception as e:
+            LOG.exception(e)
+            self.engine.notify(self._db_action,
+                               obj_action.Status.FAILED)
+            raise
+
+    def execute(self, *args, **kwargs):
+        try:
+            LOG.debug("Running action %s", self.name)
+
+            # todo(jed) remove return (true or false) raise an Exception
+            result = self.action.execute()
+            if result is not True:
+                self.engine.notify(self._db_action,
+                                   obj_action.Status.FAILED)
+            else:
+                self.engine.notify(self._db_action,
+                                   obj_action.Status.SUCCEEDED)
+        except Exception as e:
+            LOG.exception(e)
+            LOG.error(_LE('The WorkFlow Engine has failed '
+                          'to execute the action %s'), self.name)
+
+            self.engine.notify(self._db_action,
+                               obj_action.Status.FAILED)
+            raise
+
+    def post_execute(self):
+        try:
+            LOG.debug("postcondition action %s", self.name)
+            self.action.postcondition()
+        except Exception as e:
+            LOG.exception(e)
+            self.engine.notify(self._db_action,
+                               obj_action.Status.FAILED)
+            raise
+
+    def revert(self, *args, **kwargs):
+        LOG.warning(_LW("Revert action %s"), self.name)
+        try:
+            # todo(jed) do we need to update the states in case of failure ?
+            self.action.revert()
+        except Exception as e:
+            LOG.exception(e)
+            LOG.critical(_LC("Oops! We need disaster recover plan"))
+
+
+class TaskFlowNop(task.Task):
+    """This class is use in case of the workflow have only one Action.
+
+    We need at least two atoms to create a link
+    """
+    def execute(self):
+        pass