Add capabilities filter for Nova

It turns out that the ComputeCapabilitiesFilter built-in to Nova
doesn't respect capabilities passed in scheduler_hints, so we can't
use it for predictable placement.  Adding this filter to the
undercloud Nova filter list will allow us to do so.

Instead of pulling in all of Nova as a test requirement, I've added
a fake_nova module to the source tree, which is injected as 'nova'
when unit tests are being run.  A check is included to make sure
nova isn't being imported for real, as well as a README explaining
the reasoning behind the fake_nova module.

Change-Id: I0618a3b9e3c33af7cdc78db4b6994d463b8aeda9

tripleo_common/filters/capabilities_filter.py

@@ -0,0 +1,35 @@
+# Copyright 2016 Red Hat, Inc.
+#
+#    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.
+
+from nova.scheduler import filters
+
+
+class TripleOCapabilitiesFilter(filters.BaseHostFilter):
+    """Filter hosts based on capabilities in boot request
+
+    The standard Nova ComputeCapabilitiesFilter does not respect capabilities
+    requested in the scheduler_hints field, so we need a custom one in order
+    to be able to do predictable placement of nodes.
+    """
+
+    # list of hosts doesn't change within a request
+    run_filter_once_per_request = True
+
+    def host_passes(self, host_state, spec_obj):
+        host_node = host_state.stats.get('node')
+        instance_node = spec_obj.scheduler_hints.get('capabilities:node')
+        # The instance didn't request a specific node
+        if not instance_node:
+            return True
+        return host_node == instance_node[0]

tripleo_common/filters/list.py

@@ -0,0 +1,27 @@
+# Copyright 2016 Red Hat, Inc.
+#
+#    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.
+
+import nova
+
+from tripleo_common.filters import capabilities_filter
+
+
+def tripleo_filters():
+    """Return a list of filter classes for TripleO
+
+    This is a wrapper around the Nova all_filters function so we can add our
+    filters to the resulting list.
+    """
+    nova_filters = nova.scheduler.filters.all_filters()
+    return (nova_filters + [capabilities_filter.TripleOCapabilitiesFilter])

tripleo_common/tests/fake_nova/README

@@ -0,0 +1,4 @@
+We don't want to pull in all of Nova and, more importantly, all of its
+numerous dependencies just for the sake of having one class to inherit
+from in our custom filter.  Instead, this module will be injected into
+sys.modules as 'nova' when we run unit tests that rely on it.

tripleo_common/tests/fake_nova/scheduler/filters.py

@@ -0,0 +1,18 @@
+# Copyright 2016 Red Hat, Inc.
+#
+# 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.
+
+
+class BaseHostFilter(object):
+    pass

tripleo_common/tests/test_filters.py

@@ -0,0 +1,68 @@
+# Copyright 2016 Red Hat, Inc.
+#
+# 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.
+
+import sys
+
+import mock
+
+from tripleo_common.tests import base
+from tripleo_common.tests import fake_nova
+
+# See the README file in the fake_nova module directory for details on why
+# this is being done.
+if 'nova' not in sys.modules:
+    sys.modules['nova'] = fake_nova
+else:
+    raise RuntimeError('nova module already found in sys.modules.  The '
+                       'fake_nova injection should be removed.')
+from tripleo_common.filters import capabilities_filter
+
+
+class TestCapabilitiesFilter(base.TestCase):
+    def test_no_requested_node(self):
+        instance = capabilities_filter.TripleOCapabilitiesFilter()
+        host_state = mock.Mock()
+        host_state.stats.get.return_value = ''
+        spec_obj = mock.Mock()
+        spec_obj.scheduler_hints.get.return_value = []
+        self.assertTrue(instance.host_passes(host_state, spec_obj))
+
+    def test_requested_node_matches(self):
+        def mock_host_get(key):
+            if key == 'node':
+                return 'compute-0'
+            else:
+                self.fail('Unexpected key requested by filter')
+
+        def mock_spec_get(key):
+            if key == 'capabilities:node':
+                return ['compute-0']
+            else:
+                self.fail('Unexpected key requested by filter')
+
+        instance = capabilities_filter.TripleOCapabilitiesFilter()
+        host_state = mock.Mock()
+        host_state.stats.get.side_effect = mock_host_get
+        spec_obj = mock.Mock()
+        spec_obj.scheduler_hints.get.side_effect = mock_spec_get
+        self.assertTrue(instance.host_passes(host_state, spec_obj))
+
+    def test_requested_node_no_match(self):
+        instance = capabilities_filter.TripleOCapabilitiesFilter()
+        host_state = mock.Mock()
+        host_state.stats.get.return_value = 'controller-0'
+        spec_obj = mock.Mock()
+        spec_obj.scheduler_hints.get.return_value = ['compute-0']
+        self.assertFalse(instance.host_passes(host_state, spec_obj))