Added in doubt default pool filter to scheduler

If the previous filter(s) didn’t make a clear selection of one pool
and if the default pool is in the set of multiple pools,
this filter will select the default pool.

Change-Id: I26a7a2628bcb593c189d8b470fd546c060ceeab9

4 files changed, 98 insertions, 0 deletions

diff --git a/designate/scheduler/filters/in_doubt_default_pool_filter.py b/designate/scheduler/filters/in_doubt_default_pool_filter.py
new file mode 100644
index 00000000..209b3ad3
--- /dev/null
+++ b/designate/scheduler/filters/in_doubt_default_pool_filter.py
@@ -0,0 +1,56 @@
+# Copyright 2017 SAP SE
+#
+# 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 oslo_config import cfg
+
+from designate.scheduler.filters import base
+from designate import objects
+
+cfg.CONF.register_opts([
+    cfg.StrOpt('default_pool_id',
+               default='794ccc2c-d751-44fe-b57f-8894c9f5c842',
+               help="The name of the default pool"),
+], group='service:central')
+
+
+class InDoubtDefaultPoolFilter(base.Filter):
+    """If the previous filter(s) didn't make a clear selection of one pool
+    and if the default pool is in the set of multiple pools, this filter will
+    select the default pool.
+
+    This filter will pass through the pool list, if there are one or
+    less pools available to schedule to, or if the default pool is
+    not in the set of multiple pools.
+
+    .. note::
+
+        This should be used as one of the last filters.
+
+    """
+
+    name = 'in_doubt_default_pool'
+    """Name to enable in the ``[designate:central:scheduler].filters`` option
+    list
+    """
+
+    def filter(self, context, pools, zone):
+        if len(pools):
+            default_pool_id = cfg.CONF['service:central'].default_pool_id
+            default_pool = objects.Pool(id=default_pool_id)
+
+            if default_pool in pools:
+                pools = objects.PoolList()
+                pools.append(default_pool)
+
+        return pools
diff --git a/designate/tests/unit/test_scheduler/test_filters.py b/designate/tests/unit/test_scheduler/test_filters.py
index 39688b62..0becb3bc 100644
--- a/designate/tests/unit/test_scheduler/test_filters.py
+++ b/designate/tests/unit/test_scheduler/test_filters.py
@@ -23,6 +23,7 @@ from designate.scheduler.filters import default_pool_filter
 from designate.scheduler.filters import fallback_filter
 from designate.scheduler.filters import pool_id_attribute_filter
 from designate.scheduler.filters import attribute_filter
+from designate.scheduler.filters import in_doubt_default_pool_filter
 from designate import objects
 from designate import context
 from designate import policy
@@ -421,3 +422,36 @@ class SchedulerAttributeFilterTest(SchedulerFilterTest):
         pools = self.test_filter.filter(self.context, pools, self.zone)
 
         self.assertEqual(0, len(pools))
+
+
+class SchedulerInDoubtDefaultPoolFilterTest(SchedulerFilterTest):
+
+    FILTER = in_doubt_default_pool_filter.InDoubtDefaultPoolFilter
+
+    def test_pools_with_default(self):
+        pools = objects.PoolList.from_list(
+            [
+                {"id": "794ccc2c-d751-44fe-b57f-8894c9f5c842"},
+                {"id": "5fabcd37-262c-4cf3-8625-7f419434b6df"}
+            ]
+        )
+        pools = self.test_filter.filter(self.context, pools, self.zone)
+
+        self.assertEqual(pools[0].id, "794ccc2c-d751-44fe-b57f-8894c9f5c842")
+
+    def test_pools_without_default(self):
+        pools = objects.PoolList.from_list(
+            [
+                {"id": "24702e43-8a52-440f-ab74-19fc16048860"},
+                {"id": "5fabcd37-262c-4cf3-8625-7f419434b6df"}
+            ]
+        )
+        pools = self.test_filter.filter(self.context, pools, self.zone)
+
+        self.assertEqual(2, len(pools))
+
+    def test_no_pools(self):
+        pools = objects.PoolList()
+        pools = self.test_filter.filter(self.context, pools, self.zone)
+
+        self.assertEqual(0, len(pools))
diff --git a/doc/source/pools/scheduler.rst b/doc/source/pools/scheduler.rst
index 4fab7e1f..faabd5dc 100644
--- a/doc/source/pools/scheduler.rst
+++ b/doc/source/pools/scheduler.rst
@@ -102,3 +102,10 @@ Default Pool Filter
 .. autoclass:: designate.scheduler.filters.default_pool_filter.DefaultPoolFilter
     :members: name
     :show-inheritance:
+
+In Doubt Default Pool Filter
+----------------------------
+
+.. autoclass:: designate.scheduler.filters.in_doubt_default_pool_filter.InDoubtDefaultPoolFilter
+    :members: name
+    :show-inheritance:
diff --git a/setup.cfg b/setup.cfg
index 3dc1d2a2..e3923f2e 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -117,6 +117,7 @@ designate.scheduler.filters =
     random = designate.scheduler.filters.random_filter:RandomFilter
     pool_id_attribute = designate.scheduler.filters.pool_id_attribute_filter:PoolIDAttributeFilter
     default_pool = designate.scheduler.filters.default_pool_filter:DefaultPoolFilter
+    in_doubt_default_pool = designate.scheduler.filters.in_doubt_default_pool_filter:InDoubtDefaultPoolFilter
 
 designate.manage =
     database = designate.manage.database:DatabaseCommands