add hypervisor version weigher

implements: blueprint weigh-host-by-hypervisor-version
Change-Id: I36b16a388383c26bdf432030bc9e28b2fd75d120

6 files changed, 232 insertions, 0 deletions

diff --git a/doc/source/admin/scheduling.rst b/doc/source/admin/scheduling.rst
index 9071c92ac9..353514ab55 100644
--- a/doc/source/admin/scheduling.rst
+++ b/doc/source/admin/scheduling.rst
@@ -1049,6 +1049,37 @@ Otherwise, it will fall back to the
 more than one value is found for a host in aggregate metadata, the minimum
 value will be used.
 
+``HypervisorVersionWeigher``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. versionadded:: 28.0.0 (Bobcat)
+
+Weigh hosts by their relative hypervisor version reported by the virt driver.
+
+While the hypervisor_version filed for all virt drivers is an int,
+each nova virt driver uses a different algorithm to convert the hypervisor-specific
+version sequence into an int. As such the values are not directly comparable between
+hosts with different hypervisors.
+
+For example, the ironic virt driver uses the ironic API micro-version as the hypervisor
+version for a given node. The libvirt driver uses the libvirt version
+i.e. Libvirt `7.1.123` becomes `700100123` vs  Ironic `1.82` becomes `1`
+Hyper-V `6.3` becomes `6003`.
+
+If you have a mixed virt driver deployment in the ironic vs non-ironic
+case nothing special needs to be done. ironic nodes are scheduled using custom
+resource classes so ironic flavors will never match non-ironic compute nodes.
+
+If a deployment has multiple non-ironic virt drivers it is recommended to use aggregates
+to group hosts by virt driver. While this is not strictly required, it is
+desirable to avoid bias towards one virt driver.
+see :ref:`filtering_hosts_by_isolating_aggregates` and :ref:`AggregateImagePropertiesIsolation`
+for more information.
+
+The default behavior of the HypervisorVersionWeigher is to select newer hosts.
+If you prefer to invert the behavior set the
+:oslo.config:option:`filter_scheduler.hypervisor_version_weight_multiplier` option
+to a negative number and the weighing has the opposite effect of the default.
 
 Utilization-aware scheduling
 ----------------------------
diff --git a/doc/source/reference/isolate-aggregates.rst b/doc/source/reference/isolate-aggregates.rst
index f5487df912..7b493f4db9 100644
--- a/doc/source/reference/isolate-aggregates.rst
+++ b/doc/source/reference/isolate-aggregates.rst
@@ -13,6 +13,8 @@
       License for the specific language governing permissions and limitations
       under the License.
 
+.. _filtering_hosts_by_isolating_aggregates:
+
 Filtering hosts by isolating aggregates
 =======================================
 
diff --git a/nova/conf/scheduler.py b/nova/conf/scheduler.py
index c75bd07c5b..c7aa2ad76d 100644
--- a/nova/conf/scheduler.py
+++ b/nova/conf/scheduler.py
@@ -464,6 +464,49 @@ Possible values:
 * An integer or float value, where the value corresponds to the multipler
   ratio for this weigher.
 """),
+    cfg.FloatOpt("hypervisor_version_weight_multiplier",
+        default=1.0,
+        help="""
+Hypervisor Version weight multiplier ratio.
+
+The multiplier is used for weighting hosts based on the reported
+hypervisor version.
+Negative numbers indicate preferring older hosts,
+the default is to prefer newer hosts to aid with upgrades.
+
+Possible values:
+
+* An integer or float value, where the value corresponds to the multiplier
+  ratio for this weigher.
+
+Example:
+
+* Strongly prefer older hosts
+
+  .. code-block:: ini
+
+    [filter_scheduler]
+    hypervisor_version_weight_multiplier=-1000
+
+
+* Moderately prefer new hosts
+
+  .. code-block:: ini
+
+    [filter_scheduler]
+    hypervisor_version_weight_multiplier=2.5
+
+* Disable weigher influence
+
+  .. code-block:: ini
+
+    [filter_scheduler]
+    hypervisor_version_weight_multiplier=0
+
+Related options:
+
+* ``[filter_scheduler] weight_classes``
+"""),
     cfg.FloatOpt("io_ops_weight_multiplier",
         default=-1.0,
         help="""
diff --git a/nova/scheduler/weights/hypervisor_version.py b/nova/scheduler/weights/hypervisor_version.py
new file mode 100644
index 0000000000..0cd7b0a824
--- /dev/null
+++ b/nova/scheduler/weights/hypervisor_version.py
@@ -0,0 +1,39 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+"""
+Hypervisor Version Weigher. Weigh hosts by their relative hypervior version.
+
+The default is to select newer hosts.  If you prefer
+to invert the behavior set the 'hypervisor_version_weight_multiplier' option
+to a negative number and the weighing has the opposite effect of the default.
+"""
+
+import nova.conf
+from nova.scheduler import utils
+from nova.scheduler import weights
+
+CONF = nova.conf.CONF
+
+
+class HypervisorVersionWeigher(weights.BaseHostWeigher):
+
+    def weight_multiplier(self, host_state):
+        """Override the weight multiplier."""
+        return utils.get_weight_multiplier(
+            host_state, 'hypervisor_version_weight_multiplier',
+            CONF.filter_scheduler.hypervisor_version_weight_multiplier)
+
+    def _weigh_object(self, host_state, weight_properties):
+        """Higher weights win.  We want newer hosts by default."""
+        # convert None to 0
+        return host_state.hypervisor_version or 0
diff --git a/nova/tests/unit/scheduler/weights/test_weights_hypervisor_version.py b/nova/tests/unit/scheduler/weights/test_weights_hypervisor_version.py
new file mode 100644
index 0000000000..c6e4abd4cd
--- /dev/null
+++ b/nova/tests/unit/scheduler/weights/test_weights_hypervisor_version.py
@@ -0,0 +1,97 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+"""
+Tests For Scheduler hypervisor version weights.
+"""
+
+from nova.scheduler import weights
+from nova.scheduler.weights import hypervisor_version
+from nova import test
+from nova.tests.unit.scheduler import fakes
+
+
+class HypervisorVersionWeigherTestCase(test.NoDBTestCase):
+    def setUp(self):
+        super().setUp()
+        self.weight_handler = weights.HostWeightHandler()
+        self.weighers = [hypervisor_version.HypervisorVersionWeigher()]
+
+    def _get_weighed_host(self, hosts, weight_properties=None):
+        if weight_properties is None:
+            weight_properties = {}
+        return self.weight_handler.get_weighed_objects(self.weighers,
+                hosts, weight_properties)[0]
+
+    def _get_all_hosts(self):
+        host_values = [
+            ('host1', 'node1', {'hypervisor_version': 1}),
+            ('host2', 'node2', {'hypervisor_version': 200}),
+            ('host3', 'node3', {'hypervisor_version': 100}),
+            ('host4', 'node4', {'hypervisor_version': 1000}),
+        ]
+        return [fakes.FakeHostState(host, node, values)
+                for host, node, values in host_values]
+
+    def test_multiplier_default(self):
+        hostinfo_list = self._get_all_hosts()
+        weighed_host = self._get_weighed_host(hostinfo_list)
+        self.assertEqual(1.0, weighed_host.weight)
+        self.assertEqual('host4', weighed_host.obj.host)
+
+    def test_multiplier_default_full_ordering(self):
+        hostinfo_list = self._get_all_hosts()
+        weighed_hosts = self.weight_handler.get_weighed_objects(
+            self.weighers, hostinfo_list, {}
+        )
+        expected_hosts = [fakes.FakeHostState(host, node, values)
+                for host, node, values in [
+            ('host4', 'node4', {'hypervisor_version': 1000}),
+            ('host2', 'node2', {'hypervisor_version': 200}),
+            ('host3', 'node3', {'hypervisor_version': 100}),
+            ('host1', 'node1', {'hypervisor_version': 1}),
+        ]]
+        for actual, expected in zip(
+            weighed_hosts,
+            expected_hosts
+        ):
+            self.assertEqual(actual.obj.host, expected.host)
+
+    def test_multiplier_none(self):
+        multi = 0.0
+        self.flags(
+            hypervisor_version_weight_multiplier=multi,
+            group='filter_scheduler'
+        )
+        hostinfo_list = self._get_all_hosts()
+        weighed_host = self._get_weighed_host(hostinfo_list)
+        self.assertEqual(multi, weighed_host.weight)
+
+    def test_multiplier_positive(self):
+        multi = 2.0
+        self.flags(
+            hypervisor_version_weight_multiplier=multi,
+            group='filter_scheduler'
+        )
+        hostinfo_list = self._get_all_hosts()
+        weighed_host = self._get_weighed_host(hostinfo_list)
+        self.assertEqual(1.0 * multi, weighed_host.weight)
+        self.assertEqual('host4', weighed_host.obj.host)
+
+    def test_multiplier_negative(self):
+        multi = -1.0
+        self.flags(
+            hypervisor_version_weight_multiplier=multi,
+            group='filter_scheduler'
+        )
+        hostinfo_list = self._get_all_hosts()
+        weighed_host = self._get_weighed_host(hostinfo_list)
+        self.assertEqual('host1', weighed_host.obj.host)
diff --git a/releasenotes/notes/hypervisor-version-weigher-d0bba77e720edafe.yaml b/releasenotes/notes/hypervisor-version-weigher-d0bba77e720edafe.yaml
new file mode 100644
index 0000000000..31f2c70926
--- /dev/null
+++ b/releasenotes/notes/hypervisor-version-weigher-d0bba77e720edafe.yaml
@@ -0,0 +1,20 @@
+---
+features:
+  - |
+    A new hypervisor version weigher has been added to prefer selecting hosts
+    with newer hypervisors installed. For the libvirt driver, this is the version
+    of libvirt on the compute node not the version of qemu. As with all
+    weighers this is enabled by default and its behavior can be modified using
+    the new ``hypervisor_version_weight_multiplier`` config option in the
+    ``filter_scheduler`` section.
+upgrade:
+  - |
+    A new hypervisor version weigher has been added that will prefer selecting
+    hosts with a newer hypervisor installed. This can help simplify rolling
+    upgrades by preferring the already upgraded hosts when moving workloads around
+    using live or cold migration. To restore the old behavior either remove
+    the weigher from the list of enabled weighers or set
+    ``[filter_scheduler] hypervisor_version_weight_multiplier=0``. The default
+    value of the hypervisor_version_weight_multiplier is 1 so only a mild
+    preference is given to new hosts, higher values will make the effect
+    more pronounced and negative values will prefer older hosts.