Enhance Watcher Applier Engine

Add a new config option 'action_execution_rule' which is a dict type.
Its key field is strategy name and the value is 'ALWAYS' or 'ANY'.
'ALWAYS' means the callback function returns True as usual.
'ANY' means the return depends on the result of previous action
execution. The callback returns True if previous action gets failed,
and the engine continues to run the next action. If previous action
executes success, the callback returns False then the next action
will be ignored.
For strategies that aren't in 'action_execution_rule', the callback
always returns True.

If exception is throwing out during the action execution, reverting will
be triggered by taskflow. To continue executing the next action,
we return False instead of throwing an exception.

Change-Id: Ib5afa214d8d097d739aad35d18b3fe5c8e4de8fc
Implements: blueprint enhance-watcher-applier-engine

watcher/applier/workflow_engine/default.py

@@ -38,8 +38,6 @@ 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,
@@ -48,7 +46,11 @@ class DefaultWorkFlowEngine(base.BaseWorkFlowEngine):
         # all u decidable 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
+        LOG.info("decider history: %s", history)
+        if history and self.execution_rule == 'ANY':
+            return not list(history.values())[0]
+        else:
+            return True
 
     @classmethod
     def get_config_opts(cls):
@@ -59,9 +61,27 @@ class DefaultWorkFlowEngine(base.BaseWorkFlowEngine):
                 min=1,
                 required=True,
                 help='Number of workers for taskflow engine '
-                     'to execute actions.')
+                     'to execute actions.'),
+            cfg.DictOpt(
+                'action_execution_rule',
+                default={},
+                help='The execution rule for linked actions,'
+                     'the key is strategy name and '
+                     'value ALWAYS means all actions will be executed,'
+                     'value ANY means if previous action executes '
+                     'success, the next action will be ignored.'
+                     'None means ALWAYS.')
             ]
 
+    def get_execution_rule(self, actions):
+        if actions:
+            actionplan_object = objects.ActionPlan.get_by_id(
+                self.context, actions[0].action_plan_id)
+            strategy_object = objects.Strategy.get_by_id(
+                self.context, actionplan_object.strategy_id)
+            return self.config.action_execution_rule.get(
+                strategy_object.name)
+
     def execute(self, actions):
         try:
             # NOTE(jed) We want to have a strong separation of concern
@@ -72,6 +92,7 @@ class DefaultWorkFlowEngine(base.BaseWorkFlowEngine):
             # the users to change it.
             # The current implementation uses graph with linked actions.
             # todo(jed) add olso conf for retry and name
+            self.execution_rule = self.get_execution_rule(actions)
             flow = gf.Flow("watcher_flow")
             actions_uuid = {}
             for a in actions: