Set minumum boundary for workers

api_workers=0 does not disable api workers but neutron-server still
launches one api worker. Rejecting 0 helps user notice that the value
they request in config files is not honored.

Also the other rpc workers options disable the corresponding workers
completely by setting these options to 0, so setting negative values
work but does not bring any special benefit.

Change-Id: Iac16b241c71ac1068c6fbea3cc792b74bfc66c03

neutron/conf/service.py

@@ -24,19 +24,23 @@ SERVICE_OPTS = [
                default=40,
                help=_('Seconds between running periodic tasks.')),
     cfg.IntOpt('api_workers',
+               min=1,
                help=_('Number of separate API worker processes for service. '
                       'If not specified, the default is equal to the number '
                       'of CPUs available for best performance, capped by '
                       'potential RAM usage.')),
     cfg.IntOpt('rpc_workers',
+               min=0,
                help=_('Number of RPC worker processes for service. '
                       'If not specified, the default is equal to half the '
                       'number of API workers. If set to 0, no RPC worker '
                       'is launched.')),
     cfg.IntOpt('rpc_state_report_workers',
                default=1,
+               min=0,
                help=_('Number of RPC worker processes dedicated to the state '
-                      'reports queue.')),
+                      'reports queue. If set to 0, no dedicated RPC worker '
+                      'for state reports queue is launched.')),
     cfg.IntOpt('periodic_fuzzy_delay',
                default=5,
                help=_('Range of seconds to randomly delay when starting the '

neutron/tests/unit/test_service.py

@@ -92,8 +92,8 @@ class TestRunWsgiApp(base.BaseTestCase):
             workers=expected_passed_value)
         self.assertEqual(expected_call, start_call)
 
-    def test_api_workers_zero(self):
-        self._test_api_workers(0, 0)
+    def test_api_workers_one(self):
+        self._test_api_workers(1, 1)
 
     def test_api_workers_default(self):
         self._test_api_workers(None, self.worker_count)
@@ -102,7 +102,7 @@ class TestRunWsgiApp(base.BaseTestCase):
         self._test_api_workers(42, 42)
 
     def test_start_all_workers(self):
-        cfg.CONF.set_override('api_workers', 0)
+        cfg.CONF.set_override('api_workers', 1)
         mock.patch.object(service, '_get_rpc_workers').start()
         mock.patch.object(service, '_get_plugins_workers').start()
         mock.patch.object(service, '_start_workers').start()

releasenotes/notes/min-workers-8705bf4f76c8b70d.yaml

@@ -0,0 +1,11 @@
+---
+upgrade:
+  - |
+    The ``[DEFAULT] api_workers`` option no longer accepts 0 or negative
+    values. Previously 0 or a negative value was translated to 1 and
+    neutron-server launched 1 api worker.
+
+  - |
+    The ``[DEFAULT] rpc_workers`` option and
+    the ``[DEFAULT] rpc_state_report_workers`` option no longer accept negative
+    values. To disable these workers, set these options to 0.