Parse forbidden in extra_specs

Accept forbidden traits in the processing of extra_specs, with the
format of:

      trait:CUSTOM_MAGIC=forbidden

This will be transformed into required=!CUSTOM_MAGIC when the traits
are assembled into a request to GET /allocation_candidates.

Implements blueprint forbidden-traits-in-nova

Change-Id: I31e609aef47d2fea03f279e4bfdd30f072d062b4

doc/source/user/flavors.rst

@@ -632,9 +632,26 @@ Required traits
 
     The scheduler will pass required traits to the
     ``GET /allocation_candidates`` endpoint in the Placement API to include
-    only resource providers that can satisfy the required traits. Currently
-    the only valid value is ``required``. Any other value will be considered
+    only resource providers that can satisfy the required traits. In 17.0.0
+    the only valid value is ``required``. In 18.0.0 ``forbidden`` is added (see
+    below). Any other value will be considered
     invalid.
 
     The FilterScheduler is currently the only scheduler driver that supports
     this feature.
+
+Forbidden traits
+    Added in the 18.0.0 Rocky release.
+
+    Forbidden traits are similar to required traits, described above, but
+    instead of specifying the set of traits that must be satisfied by a compute
+    node, forbidden traits must **not** be present.
+
+    The syntax of the extra spec is ``trait:<trait_name>=forbidden``, for
+    example:
+
+    - trait:HW_CPU_X86_AVX2=forbidden
+    - trait:STORAGE_DISK_SSD=forbidden
+
+    The FilterScheduler is currently the only scheduler driver that supports
+    this feature.

nova/scheduler/client/report.py

@@ -339,6 +339,7 @@ def get_allocation_candidates(self, context, resources):
         # and traits in the query string (via a new method on ResourceRequest).
         res = resources.get_request_group(None).resources
         required_traits = resources.get_request_group(None).required_traits
+        forbidden_traits = resources.get_request_group(None).forbidden_traits
         aggregates = resources.get_request_group(None).member_of
 
         resource_query = ",".join(
@@ -350,6 +351,14 @@ def get_allocation_candidates(self, context, resources):
         }
         if required_traits:
             qs_params['required'] = ",".join(required_traits)
+        if forbidden_traits:
+            # Sorted to make testing easier to manage and for
+            # predictability.
+            forbiddens = ',!'.join(sorted(forbidden_traits))
+            if qs_params['required']:
+                qs_params['required'] += ',!' + forbiddens
+            else:
+                qs_params['required'] = '!' + forbiddens
         if aggregates:
             # NOTE(danms): In 1.21, placement cannot take an AND'd
             # set of aggregates, only an OR'd set. Thus, if we have

nova/scheduler/utils.py

@@ -85,17 +85,20 @@ def _add_resource(self, groupid, rclass, amount):
         self.get_request_group(groupid).resources[rclass] = amount
 
     def _add_trait(self, groupid, trait_name, trait_type):
-        # Currently the only valid value for a trait entry is 'required'.
-        trait_vals = ('required',)
-        # Ensure the value is supported.
-        if trait_type not in trait_vals:
+        # Currently the only valid values for a trait entry are 'required'
+        # and 'forbidden'
+        trait_vals = ('required', 'forbidden')
+        if trait_type == 'required':
+            self.get_request_group(groupid).required_traits.add(trait_name)
+        elif trait_type == 'forbidden':
+            self.get_request_group(groupid).forbidden_traits.add(trait_name)
+        else:
             LOG.warning(
                 "Only (%(tvals)s) traits are supported. Received '%(val)s' "
                 "for key trait%(groupid)s.",
                 {"tvals": ', '.join(trait_vals), "groupid": groupid,
                  "val": trait_type})
-            return
-        self.get_request_group(groupid).required_traits.add(trait_name)
+        return
 
     @classmethod
     def from_extra_specs(cls, extra_specs):

nova/tests/unit/scheduler/client/test_report.py

@@ -1421,14 +1421,18 @@ def test_get_allocation_candidates(self):
             'resources1:DISK_GB': '30',
             'trait:CUSTOM_TRAIT1': 'required',
             'trait:CUSTOM_TRAIT2': 'preferred',
+            'trait:CUSTOM_TRAIT3': 'forbidden',
+            'trait:CUSTOM_TRAIT4': 'forbidden',
         })
         resources.get_request_group(None).member_of = [
             ('agg1', 'agg2', 'agg3'), ('agg1', 'agg2')]
         expected_path = '/allocation_candidates'
-        expected_query = {'resources': ['MEMORY_MB:1024,VCPU:1'],
-                          'required': ['CUSTOM_TRAIT1'],
-                          'member_of': ['in:agg1,agg2'],
-                          'limit': ['1000']}
+        expected_query = {
+            'resources': ['MEMORY_MB:1024,VCPU:1'],
+            'required': ['CUSTOM_TRAIT1,!CUSTOM_TRAIT3,!CUSTOM_TRAIT4'],
+            'member_of': ['in:agg1,agg2'],
+            'limit': ['1000']
+        }
 
         resp_mock.json.return_value = json_data
         self.ks_adap_mock.get.return_value = resp_mock

nova/tests/unit/scheduler/test_utils.py

@@ -373,6 +373,7 @@ def test_resource_request_from_extra_specs(self):
             # Key skipped because no colons
             'nocolons': '42',
             'trait:CUSTOM_MAGIC': 'required',
+            'trait:CUSTOM_BRONZE': 'forbidden',
             # Resource skipped because invalid resource class name
             'resources86:CUTSOM_MISSPELLED': '86',
             'resources1:SRIOV_NET_VF': '1',
@@ -384,6 +385,7 @@ def test_resource_request_from_extra_specs(self):
             # Trait skipped because unsupported value
             'trait86:CUSTOM_GOLD': 'preferred',
             'trait1:CUSTOM_PHYSNET_NET1': 'required',
+            'trait1:CUSTOM_PHYSNET_NET2': 'forbidden',
             'resources2:SRIOV_NET_VF': '1',
             'resources2:IPV4_ADDRESS': '2',
             'trait2:CUSTOM_PHYSNET_NET2': 'required',
@@ -405,7 +407,10 @@ def test_resource_request_from_extra_specs(self):
             required_traits={
                 'HW_CPU_X86_AVX',
                 'CUSTOM_MAGIC',
-            }
+            },
+            forbidden_traits={
+                'CUSTOM_BRONZE',
+            },
         )
         expected._rg_by_id['1'] = plib.RequestGroup(
             resources={
@@ -414,7 +419,10 @@ def test_resource_request_from_extra_specs(self):
             },
             required_traits={
                 'CUSTOM_PHYSNET_NET1',
-            }
+            },
+            forbidden_traits={
+                'CUSTOM_PHYSNET_NET2',
+            },
         )
         expected._rg_by_id['2'] = plib.RequestGroup(
             resources={

releasenotes/notes/forbidden-traits-in-nova-478f1884a06e50e7.yaml

@@ -0,0 +1,21 @@
+---
+features:
+  - |
+    Added support for forbidden traits to the scheduler. A flavor extra spec
+    is extended to support specifying the forbidden traits. The syntax of
+    extra spec is ``trait:<trait_name>=forbidden``, for example:
+
+    - trait:HW_CPU_X86_AVX2=forbidden
+    - trait:STORAGE_DISK_SSD=forbidden
+
+    The scheduler will pass the forbidden traits to the
+    ``GET /allocation_candidates`` endpoint in the Placement API to include
+    only resource providers that do not include the forbidden traits. Currently
+    the only valid values are ``required`` and ``forbidden``. Any other values
+    will be considered invalid.
+
+    This requires that the Placement API version 1.22 is available before
+    the ``nova-scheduler`` service can use this feature.
+
+    The FilterScheduler is currently the only scheduler driver that supports
+    this feature.