Not allow overcommit ratios to be negative

Currently the three overcommit ratios: ram_allocation_ratio,
cpu_allocation_ratio, and disk_allocation_ratio can be set to negative values.
It's up to the scheduler filters to impose the checks on these ratios.

It makes more sense to make sure these 3 ratios are not negative when
nova-compute is started.  If any of these ratios is negative then nova-compute
service will fail to start.

Closes-Bug: #1604116
Change-Id: Ic960e319b59910c0178e81259b2e35435f2db592

nova/conf/compute.py

@@ -189,6 +189,7 @@ Possible values
 allocation_ratio_opts = [
     cfg.FloatOpt('cpu_allocation_ratio',
         default=0.0,
+        min=0.0,
         help="""
 This option helps you specify virtual CPU to physical CPU allocation
 ratio which affects all CPU filters.
@@ -208,6 +209,7 @@ and defaulted to 16.0'.
 """),
     cfg.FloatOpt('ram_allocation_ratio',
         default=0.0,
+        min=0.0,
         help="""
 This option helps you specify virtual RAM to physical RAM
 allocation ratio which affects all RAM filters.
@@ -227,6 +229,7 @@ defaulted to 1.5.
 """),
     cfg.FloatOpt('disk_allocation_ratio',
         default=0.0,
+        min=0.0,
         help="""
 This option helps you specify virtual disk to physical disk
 allocation ratio used by the disk_filter.py script to determine if

nova/tests/unit/compute/test_resource_tracker.py

@@ -14,6 +14,7 @@ import copy
 import datetime
 
 import mock
+from oslo_config import cfg
 from oslo_utils import timeutils
 from oslo_utils import units
 
@@ -38,6 +39,7 @@ from nova.tests import uuidsentinel as uuids
 
 _HOSTNAME = 'fake-host'
 _NODENAME = 'fake-node'
+CONF = cfg.CONF
 
 _VIRT_DRIVER_AVAIL_RESOURCES = {
     'vcpus': 4,
@@ -2270,3 +2272,20 @@ class TestIsTrackableMigration(test.NoDBTestCase):
             mig.migration_type = mig_type
 
             self.assertFalse(resource_tracker._is_trackable_migration(mig))
+
+
+class OverCommitTestCase(BaseTestCase):
+    def test_cpu_allocation_ratio_none_negative(self):
+        self.assertRaises(ValueError,
+                          CONF.set_default, 'cpu_allocation_ratio', -1.0,
+                          enforce_type=True)
+
+    def test_ram_allocation_ratio_none_negative(self):
+        self.assertRaises(ValueError,
+                          CONF.set_default, 'ram_allocation_ratio', -1.0,
+                          enforce_type=True)
+
+    def test_disk_allocation_ratio_none_negative(self):
+        self.assertRaises(ValueError,
+                          CONF.set_default, 'disk_allocation_ratio', -1.0,
+                          enforce_type=True)

releasenotes/notes/bug-1604116-87a823c3c165d057.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - The three configuration options ``cpu_allocation_ratio``,
+    ``ram_allocation_ratio`` and ``disk_allocation_ratio`` for
+    the nova compute are now checked against negative values.
+    If any of these three options is set to negative value
+    then nova compute service will fail to start.