cassandra cluster no load-balancing policy

monasca-api connect to cassandra cluster without
load-balancing policy parameter.
Task: 29958
Story: 2005196

Change-Id: Ia740f20f6b8d557a74a48cd0c78cd07c1500ca94

monasca_api/common/repositories/cassandra/metrics_repository.py

@@ -23,6 +23,8 @@ import urllib
 
 from cassandra.auth import PlainTextAuthProvider
 from cassandra.cluster import Cluster
+from cassandra.cluster import DCAwareRoundRobinPolicy
+from cassandra.cluster import TokenAwarePolicy
 from cassandra.query import FETCH_SIZE_UNSET
 from cassandra.query import SimpleStatement
 from monasca_common.rest import utils as rest_utils
@@ -120,7 +122,12 @@ class MetricsRepository(metrics_repository.AbstractMetricsRepository):
                 auth_provider = None
 
             self.cluster = Cluster(self.conf.cassandra.contact_points,
-                                   port=self.conf.cassandra.port, auth_provider=auth_provider)
+                                   port=self.conf.cassandra.port,
+                                   auth_provider=auth_provider,
+                                   load_balancing_policy=TokenAwarePolicy(
+                                       DCAwareRoundRobinPolicy(
+                                           local_dc=self.conf.cassandra.local_data_center))
+                                   )
             self.session = self.cluster.connect(self.conf.cassandra.keyspace)
 
             self.dim_val_by_metric_stmt = self.session.prepare(DIMENSION_VALUE_BY_METRIC_CQL)

monasca_api/conf/cassandra.py

@@ -40,6 +40,10 @@ Cassandra user for monasca-api service
     cfg.StrOpt('password', default='', secret=True,
                help='''
 Cassandra user password for monasca-api service
+'''),
+    cfg.StrOpt('local_data_center', default='',
+               help='''
+Cassandra local data center name
 ''')
 ]
 

releasenotes/notes/add-cassandra-loadbalancing-policy-4d5d0e7e8064a870.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    support cassandra cluster configuration with loadbalancing policy DCAwareRoundRobinPolicy.
+    'local_data_center' defalut value is ''.