Switch TaskFlow engine to parallel

The default TaskFlow engine is now set to 'parallel' instead of
'serial'. The parallel engine schedules tasks onto different threads to
allow for running non-dependent tasks simultaneously. This has the
benefit of accelerating the execution of some Octavia Amphora flows such
as provisioning of active-standby amphora loadbalancers.

Change-Id: I108b7f629d39c40b60ddf4a1878631f32e37b357

etc/octavia.conf

@@ -254,7 +254,12 @@
 # user_data_config_drive = False
 
 [task_flow]
-# engine = serial
+# TaskFlow engine options are:
+#   - serial:   Runs all tasks on a single thread.
+#   - parallel: Schedules tasks onto different threads to allow
+#               for running non-dependent tasks simultaneously
+#
+# engine = parallel
 # max_workers = 5
 #
 # This setting prevents the controller worker from reverting taskflow flows.

octavia/common/config.py

@@ -429,8 +429,12 @@ controller_worker_opts = [
 
 task_flow_opts = [
     cfg.StrOpt('engine',
-               default='serial',
+               default='parallel',
-               help=_('TaskFlow engine to use')),
+               choices=constants.SUPPORTED_TASKFLOW_ENGINE_TYPES,
+               help=_('TaskFlow engine to use. '
+                      'serial - Runs all tasks on a single thread. '
+                      'parallel - Schedules tasks onto different threads to '
+                      'allow for running non-dependent tasks simultaneously')),
     cfg.IntOpt('max_workers',
                default=5,
                help=_('The maximum number of workers')),

octavia/common/constants.py

@@ -280,6 +280,9 @@ HTTP_QUOTED_HEADER_VALUE_REGEX = (r'\A"[a-zA-Z0-9 \t'
 DOMAIN_NAME_REGEX = (
     r'^(?=.{1,253}\.?$)(?:(?!-|[^.]+_)[A-Za-z0-9-_]{1,63}(?<!-)(?:\.|$))+$')
 
+# TaskFlow
+SUPPORTED_TASKFLOW_ENGINE_TYPES = ['serial', 'parallel']
+
 # Task/Flow constants
 AMPHORA = 'amphora'
 FAILED_AMPHORA = 'failed_amphora'

octavia/tests/unit/common/test_base_taskflow.py

@@ -25,6 +25,7 @@ import octavia.tests.unit.base as base
 
 
 MAX_WORKERS = 1
+ENGINE = 'parallel'
 
 _engine_mock = mock.MagicMock()
 
@@ -35,7 +36,7 @@ class TestBaseTaskFlowEngine(base.TestCase):
 
         conf = oslo_fixture.Config(cfg.CONF)
         conf.config(group="task_flow", max_workers=MAX_WORKERS)
-        conf.config(group="task_flow", engine='TESTENGINE')
+        conf.config(group="task_flow", engine=ENGINE)
         conf.config(group="task_flow", disable_revert=True)
         super(TestBaseTaskFlowEngine, self).setUp()
 
@@ -60,7 +61,7 @@ class TestBaseTaskFlowEngine(base.TestCase):
 
         tf_engines.load.assert_called_once_with(
             'TEST',
-            engine='TESTENGINE',
+            engine=ENGINE,
             executor='TESTEXECUTOR',
             never_resolve=True)
 

releasenotes/notes/switch-taskflow-engine-parallel-8bf743eca15a0253.yaml

@@ -0,0 +1,10 @@
+---
+upgrade:
+  - |
+    The default TaskFlow engine is now set to 'parallel' instead of 'serial'.
+    The parallel engine schedules tasks onto different threads to allow for
+    running non-dependent tasks simultaneously. This has the benefit of
+    accelerating the execution of some Octavia Amphora flows such as
+    provisioning of active-standby amphora loadbalancers. Operators can revert
+    to previously default 'serial' engine type by setting the configuration
+    option [task_flow]/engine = serial