From 0978c776a2c9f6cc992a8fcf0d06c981d98d9412 Mon Sep 17 00:00:00 2001
From: Carlos Goncalves <cgoncalves@redhat.com>
Date: Wed, 14 Aug 2019 11:26:29 +0200
Subject: [PATCH] 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                                       |  7 ++++++-
 octavia/common/config.py                               |  8 ++++++--
 octavia/common/constants.py                            |  3 +++
 octavia/tests/unit/common/test_base_taskflow.py        |  5 +++--
 ...itch-taskflow-engine-parallel-8bf743eca15a0253.yaml | 10 ++++++++++
 5 files changed, 28 insertions(+), 5 deletions(-)
 create mode 100644 releasenotes/notes/switch-taskflow-engine-parallel-8bf743eca15a0253.yaml

diff --git a/etc/octavia.conf b/etc/octavia.conf
index 66268d7089..c1d664fbe2 100644
--- a/etc/octavia.conf
+++ b/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.
diff --git a/octavia/common/config.py b/octavia/common/config.py
index fbd85a1a97..413932f8c1 100644
--- a/octavia/common/config.py
+++ b/octavia/common/config.py
@@ -429,8 +429,12 @@ controller_worker_opts = [
 
 task_flow_opts = [
     cfg.StrOpt('engine',
-               default='serial',
-               help=_('TaskFlow engine to use')),
+               default='parallel',
+               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')),
diff --git a/octavia/common/constants.py b/octavia/common/constants.py
index 1155708ec6..0944b56087 100644
--- a/octavia/common/constants.py
+++ b/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'
diff --git a/octavia/tests/unit/common/test_base_taskflow.py b/octavia/tests/unit/common/test_base_taskflow.py
index 04da83e164..e36de3f002 100644
--- a/octavia/tests/unit/common/test_base_taskflow.py
+++ b/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)
 
diff --git a/releasenotes/notes/switch-taskflow-engine-parallel-8bf743eca15a0253.yaml b/releasenotes/notes/switch-taskflow-engine-parallel-8bf743eca15a0253.yaml
new file mode 100644
index 0000000000..1b48a433c4
--- /dev/null
+++ b/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