Refactors scheduler.chance.select_hosts to raise NoValidHost

This change is intended to refactor the method to be consistent
with the filter_scheduler.select_hosts implementation.

This method is called by scheduler.manager and it is exposed
through the scheduler.rpcapi. Thus, both implementations should
behave the same.

This change is needed by others that will move cold migration
to conductor.

Partially implements bp cold-migrations-to-conductor

Change-Id: I0f6fef43324cf829cdb26633874c537572423f77

4 files changed, 26 insertions, 1 deletions

diff --git a/nova/scheduler/chance.py b/nova/scheduler/chance.py
index 6e9688d81..0f8f3c45a 100644
--- a/nova/scheduler/chance.py
+++ b/nova/scheduler/chance.py
@@ -60,9 +60,12 @@ class ChanceScheduler(driver.Scheduler):
 
     def select_hosts(self, context, request_spec, filter_properties):
         """Selects a set of random hosts."""
-        return [self._schedule(context, CONF.compute_topic,
+        hosts = [self._schedule(context, CONF.compute_topic,
             request_spec, filter_properties)
             for instance_uuid in request_spec.get('instance_uuids', [])]
+        if not hosts:
+            raise exception.NoValidHost(reason="")
+        return hosts
 
     def schedule_run_instance(self, context, request_spec,
                               admin_password, injected_files,
diff --git a/nova/tests/scheduler/test_chance_scheduler.py b/nova/tests/scheduler/test_chance_scheduler.py
index a589000cd..8a281073a 100644
--- a/nova/tests/scheduler/test_chance_scheduler.py
+++ b/nova/tests/scheduler/test_chance_scheduler.py
@@ -194,3 +194,12 @@ class ChanceSchedulerTestCase(test_scheduler.SchedulerTestCase):
         self.mox.ReplayAll()
         hosts = self.driver.select_hosts(ctxt, request_spec, {})
         self.assertEquals(['host3', 'host1'], hosts)
+
+    def test_select_hosts_no_valid_host(self):
+
+        def _return_no_host(*args, **kwargs):
+            return []
+
+        self.stubs.Set(self.driver, '_schedule', _return_no_host)
+        self.assertRaises(exception.NoValidHost,
+                          self.driver.select_hosts, self.context, {}, {})
diff --git a/nova/tests/scheduler/test_filter_scheduler.py b/nova/tests/scheduler/test_filter_scheduler.py
index 80680dda8..a4aba4207 100644
--- a/nova/tests/scheduler/test_filter_scheduler.py
+++ b/nova/tests/scheduler/test_filter_scheduler.py
@@ -707,3 +707,12 @@ class FilterSchedulerTestCase(test_scheduler.SchedulerTestCase):
         hosts = sched.select_hosts(fake_context, request_spec, {})
         self.assertEquals(len(hosts), 10)
         self.assertEquals(hosts, selected_hosts)
+
+    def test_select_hosts_no_valid_host(self):
+
+        def _return_no_host(*args, **kwargs):
+            return []
+
+        self.stubs.Set(self.driver, '_schedule', _return_no_host)
+        self.assertRaises(exception.NoValidHost,
+                          self.driver.select_hosts, self.context, {}, {})
diff --git a/nova/tests/scheduler/test_scheduler.py b/nova/tests/scheduler/test_scheduler.py
index f4f607647..fc5c4787b 100644
--- a/nova/tests/scheduler/test_scheduler.py
+++ b/nova/tests/scheduler/test_scheduler.py
@@ -951,6 +951,10 @@ class SchedulerDriverBaseTestCase(SchedulerTestCase):
                          self.context, {},
                          fake_request_spec, {}, {}, {}, None)
 
+    def test_unimplemented_select_hosts(self):
+        self.assertRaises(NotImplementedError,
+                          self.driver.select_hosts, self.context, {}, {})
+
 
 class SchedulerDriverModuleTestCase(test.TestCase):
     """Test case for scheduler driver module methods."""