Require mongodb >= 2.2 or fail misserably

The patch adds a minimum requirement for mongodb. This will provide a
useful error message to users when the installed mongodb version doesn't
match the minimum required one.

Change-Id: Iff8bb1645e7276529230da58c408552bebd8647a

tests/unit/queues/storage/test_impl_mongodb.py

@@ -151,6 +151,21 @@ class MongodbDriverTest(MongodbSetupMixin, testing.TestBase):
             self.assertThat(db.name, matchers.StartsWith(
                 driver.mongodb_conf.database))
 
+    def test_version_match(self):
+        cache = oslo_cache.get_cache()
+
+        with mock.patch('pymongo.MongoClient.server_info') as info:
+            info.return_value = {'version': '2.1'}
+            self.assertRaises(RuntimeError, mongodb.DataDriver,
+                              self.conf, cache)
+
+            info.return_value = {'version': '2.11'}
+
+            try:
+                mongodb.DataDriver(self.conf, cache)
+            except RuntimeError:
+                self.fail('version match failed')
+
 
 @testing.requires_mongodb
 class MongodbQueueTests(MongodbSetupMixin, base.QueueControllerTest):

zaqar/queues/storage/mongodb/driver.py

@@ -21,6 +21,7 @@ import pymongo
 import pymongo.errors
 
 from zaqar.common import decorators
+from zaqar.i18n import _
 from zaqar.openstack.common import log as logging
 from zaqar.queues import storage
 from zaqar.queues.storage.mongodb import controllers
@@ -81,6 +82,11 @@ class DataDriver(storage.DataDriverBase):
                                 group=options.MONGODB_GROUP)
         self.mongodb_conf = self.conf[options.MONGODB_GROUP]
 
+        server_version = self.connection.server_info()['version']
+        if tuple(map(int, server_version.split('.'))) < (2, 2):
+            raise RuntimeError(_('The mongodb driver requires mongodb>=2.2,  '
+                                 '%s found') % server_version)
+
     def is_alive(self):
         try:
             # NOTE(zyuan): Requires admin access to mongodb