Only auto-disable new nova-compute services

Change If1e03c9343b8cc9c34bd51c2b4d25acdb21131ff made the
os-services REST API only able to perform PUT actions on
nova-compute services, since those are the only ones with
host mappings in the API database. Attempting to enable or
disable a nova-scheduler service, for example, will fail with a
404 error now.

The enable_new_services config option is used to auto-disable
newly registered services to test them out before bringing them
into the pool of services for scheduling. This was really only
intended, and only makes sense for, nova-compute services. Disabling
scheduler, conductor, or API services does nothing functionally, and
requires the operator to later enable those services just to make
the GET /os-services output make sense.

This change makes the enable_new_services config option only have
an effect on auto-disabling new nova-compute services. All other
services are ignored and will not be auto-disabled. The config
option help text is updated to make this clear.

Change-Id: Ie9cb44d3f87ba85420e2909170f4d207ec4bf717
Closes-Bug: #1697960

nova/conf/compute.py

@@ -1098,19 +1098,21 @@ Possible values:
     cfg.BoolOpt('enable_new_services',
         default=True,
         help="""
-Enable new services on this host automatically.
+Enable new nova-compute services on this host automatically.
 
-When a new service (for example "nova-compute") starts up, it gets
+When a new nova-compute service starts up, it gets
 registered in the database as an enabled service. Sometimes it can be useful
-to register new services in disabled state and then enabled them at a later
-point in time. This option can set this behavior for all services per host.
+to register new compute services in disabled state and then enabled them at a
+later point in time. This option only sets this behavior for nova-compute
+services, it does not auto-disable other services like nova-conductor,
+nova-scheduler, nova-consoleauth, or nova-osapi_compute.
 
 Possible values:
 
-* ``True``: Each new service is enabled as soon as it registers itself.
-* ``False``: Services must be enabled via a REST API call or with the CLI
-  with ``nova service-enable <hostname> <binary>``, otherwise they are not
-  ready to use.
+* ``True``: Each new compute service is enabled as soon as it registers itself.
+* ``False``: Compute services must be enabled via an os-services REST API call
+  or with the CLI with ``nova service-enable <hostname> <binary>``, otherwise
+  they are not ready to use.
 """),
     cfg.StrOpt('instance_name_template',
          default='instance-%08x',

nova/db/sqlalchemy/api.py

@@ -585,8 +585,13 @@ def service_get_by_compute_host(context, host):
 def service_create(context, values):
     service_ref = models.Service()
     service_ref.update(values)
-    if not CONF.enable_new_services:
-        msg = _("New service disabled due to config option.")
+    # We only auto-disable nova-compute services since those are the only
+    # ones that can be enabled using the os-services REST API and they are
+    # the only ones where being disabled means anything. It does
+    # not make sense to be able to disable non-compute services like
+    # nova-scheduler or nova-osapi_compute since that does nothing.
+    if not CONF.enable_new_services and values.get('binary') == 'nova-compute':
+        msg = _("New compute service disabled due to config option.")
         service_ref.disabled = True
         service_ref.disabled_reason = msg
     try:

nova/tests/unit/db/test_db_api.py

@@ -3515,15 +3515,24 @@ class ServiceTestCase(test.TestCase, ModelsObjectComparatorMixin):
 
     def test_service_create_disabled(self):
         self.flags(enable_new_services=False)
-        service = self._create_service({})
+        service = self._create_service({'binary': 'nova-compute'})
         self.assertTrue(service['disabled'])
 
     def test_service_create_disabled_reason(self):
         self.flags(enable_new_services=False)
-        service = self._create_service({})
-        msg = "New service disabled due to config option."
+        service = self._create_service({'binary': 'nova-compute'})
+        msg = "New compute service disabled due to config option."
         self.assertEqual(msg, service['disabled_reason'])
 
+    def test_service_create_disabled_non_compute_ignored(self):
+        """Tests that enable_new_services=False has no effect on
+        auto-disabling a new non-nova-compute service.
+        """
+        self.flags(enable_new_services=False)
+        service = self._create_service({'binary': 'nova-scheduler'})
+        self.assertFalse(service['disabled'])
+        self.assertIsNone(service['disabled_reason'])
+
     def test_service_destroy(self):
         service1 = self._create_service({})
         service2 = self._create_service({'host': 'fake_host2'})

releasenotes/notes/enable_new_services-compute-only-0abf5d3cbec40eb2.yaml

@@ -0,0 +1,9 @@
+---
+other:
+  - |
+    The ``[DEFAULT]/enable_new_services`` configuration option will now only be
+    used to auto-disable new nova-compute services. Other services like
+    nova-conductor, nova-scheduler and nova-osapi_compute will not be
+    auto-disabled since disabling them does nothing functionally, and starting
+    in Pike the ``PUT /os-services/enable`` REST API will not be able to find
+    non-compute services to enable them.