diff --git a/.zuul.yaml b/.zuul.yaml
index 44947e943..663c8ee32 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -129,6 +129,7 @@
 - job:
     name: monasca-tempest-python3-influxdb
     parent: monasca-tempest-base
+    voting: false
     vars:
       devstack_localrc:
         MONASCA_API_IMPLEMENTATION_LANG: python
@@ -206,21 +207,12 @@
         - monasca-tempest-log-python3-influxdb
         - monasca-tempest-python3-influxdb
         - monasca-tempest-python3-cassandra
-        - build-monasca-docker-image
+        - build-monasca-docker-image:
+            voting: false
     gate:
       queue: monasca
       jobs:
         - monasca-tempest-log-python3-influxdb
-        - monasca-tempest-python3-influxdb
-    post:
-      jobs:
-        - publish-monasca-api-docker-image
-    periodic:
-      jobs:
-        - publish-monasca-api-docker-image
-    release:
-      jobs:
-        - publish-monasca-api-docker-image
 
 - job:
     name: publish-monasca-api-docker-image
diff --git a/lower-constraints.txt b/lower-constraints.txt
index 6a3acc6cc..f66f0a94c 100644
--- a/lower-constraints.txt
+++ b/lower-constraints.txt
@@ -97,6 +97,7 @@ requestsexceptions==1.2.0
 requests-mock==1.2.0
 restructuredtext-lint==1.1.1
 rfc3986==0.3.1
+simplejson==3.8.1
 six==1.10.0
 smmap==0.9.0
 snowballstemmer==1.2.1
@@ -115,7 +116,6 @@ testrepository==0.0.18
 testscenarios==0.4
 testtools==2.2.0
 traceback2==1.4.0
-ujson==1.35
 unittest2==1.1.0
 urllib3==1.21.1
 voluptuous==0.8.9
diff --git a/monasca_api/api/core/log/log_publisher.py b/monasca_api/api/core/log/log_publisher.py
index 01886fe20..85495d7b6 100644
--- a/monasca_api/api/core/log/log_publisher.py
+++ b/monasca_api/api/core/log/log_publisher.py
@@ -16,8 +16,8 @@
 import time
 
 import falcon
+from monasca_api.common.rest import utils as rest_utils
 from monasca_common.kafka import client_factory
-from monasca_common.rest import utils as rest_utils
 from oslo_log import log
 from oslo_utils import encodeutils
 
diff --git a/monasca_api/api/core/log/model.py b/monasca_api/api/core/log/model.py
index 4a24739e4..687cf4141 100644
--- a/monasca_api/api/core/log/model.py
+++ b/monasca_api/api/core/log/model.py
@@ -15,7 +15,7 @@
 from oslo_utils import timeutils
 import six
 
-from monasca_common.rest import utils as rest_utils
+from monasca_api.common.rest import utils as rest_utils
 
 
 def serialize_envelope(envelope):
diff --git a/monasca_api/common/rest/utils.py b/monasca_api/common/rest/utils.py
index 87b36c522..f6c33b35a 100644
--- a/monasca_api/common/rest/utils.py
+++ b/monasca_api/common/rest/utils.py
@@ -12,8 +12,8 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import simplejson as json
 import six
-import ujson as json
 
 from monasca_api.common.rest import exceptions
 
diff --git a/monasca_api/tests/test_helpers.py b/monasca_api/tests/test_helpers.py
index 7dc1c7f96..231477eca 100644
--- a/monasca_api/tests/test_helpers.py
+++ b/monasca_api/tests/test_helpers.py
@@ -22,7 +22,7 @@ from monasca_api.common.policy import policy_engine as policy
 from monasca_api.tests import base
 import monasca_api.v2.reference.helpers as helpers
 
-from monasca_common.rest import utils as rest_utils
+from monasca_api.common.rest import utils as rest_utils
 
 
 class TestHelpersFunction(base.BaseTestCase):
@@ -47,7 +47,7 @@ class TestHelpersFunction(base.BaseTestCase):
 
     def test_to_json(self):
         test_dict = {'test_body': 'test'}
-        expected_json = '{"test_body":"test"}'
+        expected_json = '{"test_body": "test"}'
         response = helpers.to_json(test_dict)
         self.assertEqual(expected_json, response)
 
diff --git a/monasca_api/tests/test_log_publisher.py b/monasca_api/tests/test_log_publisher.py
index d53c201ae..9cd49a969 100644
--- a/monasca_api/tests/test_log_publisher.py
+++ b/monasca_api/tests/test_log_publisher.py
@@ -20,8 +20,8 @@ import random
 import mock
 from oslo_config import cfg
 from oslo_log import log
+import simplejson as json
 import six
-import ujson
 import unittest
 
 from monasca_api.api.core.log import log_publisher
@@ -132,7 +132,7 @@ class TestSendMessage(base.BaseTestCase):
 
         instance._kafka_publisher.publish.assert_called_once_with(
             cfg.CONF.kafka.logs_topics[0],
-            [ujson.dumps(msg, ensure_ascii=False).encode('utf-8')])
+            [json.dumps(msg, ensure_ascii=False).encode('utf-8')])
 
     @mock.patch('monasca_api.api.core.log.log_publisher.client_factory'
                 '.get_kafka_producer')
@@ -168,7 +168,7 @@ class TestSendMessage(base.BaseTestCase):
             }
         )
         msg['creation_time'] = creation_time
-        json_msg = ujson.dumps(msg, ensure_ascii=False)
+        json_msg = json.dumps(msg, ensure_ascii=False)
 
         instance.send_message(msg)
 
@@ -203,7 +203,7 @@ class TestSendMessage(base.BaseTestCase):
                 )
                 instance.send_message(envelope)
 
-                expected_message = ujson.dumps(envelope, ensure_ascii=False)
+                expected_message = json.dumps(envelope, ensure_ascii=False)
 
                 if six.PY3:
                     expected_message = expected_message.encode('utf-8')
@@ -220,7 +220,7 @@ class TestSendMessage(base.BaseTestCase):
 @mock.patch('monasca_api.api.core.log.log_publisher.client_factory'
             '.get_kafka_producer')
 class TestTruncation(base.BaseTestCase):
-    EXTRA_CHARS_SIZE = len(bytearray(ujson.dumps({
+    EXTRA_CHARS_SIZE = len(bytearray(json.dumps({
         'log': {
             'message': None
         }
@@ -276,7 +276,7 @@ class TestTruncation(base.BaseTestCase):
         envelope_copy = copy.deepcopy(envelope)
         json_envelope = instance._truncate(envelope_copy)
 
-        parsed_envelope = ujson.loads(json_envelope)
+        parsed_envelope = json.loads(json_envelope)
 
         parsed_log_message = parsed_envelope['log']['message']
         parsed_log_message_len = len(parsed_log_message)
diff --git a/monasca_api/tests/test_logs.py b/monasca_api/tests/test_logs.py
index a355eb0de..00a5a6542 100644
--- a/monasca_api/tests/test_logs.py
+++ b/monasca_api/tests/test_logs.py
@@ -14,7 +14,7 @@
 
 import falcon
 import mock
-import ujson as json
+import simplejson as json
 
 from monasca_api.tests import base
 from monasca_api.v2.reference import logs
diff --git a/monasca_api/v2/common/helpers.py b/monasca_api/v2/common/helpers.py
index b38ad06fc..925d62071 100644
--- a/monasca_api/v2/common/helpers.py
+++ b/monasca_api/v2/common/helpers.py
@@ -20,7 +20,7 @@ from oslo_log import log
 
 from monasca_api.api.core.log import exceptions
 from monasca_api.api.core.log import validation
-from monasca_common.rest import utils as rest_utils
+from monasca_api.common.rest import utils as rest_utils
 
 
 LOG = log.getLogger(__name__)
diff --git a/monasca_api/v2/reference/helpers.py b/monasca_api/v2/reference/helpers.py
index c0f540a30..9f5c240f9 100644
--- a/monasca_api/v2/reference/helpers.py
+++ b/monasca_api/v2/reference/helpers.py
@@ -24,9 +24,9 @@ from oslo_utils import timeutils
 import six
 import six.moves.urllib.parse as urlparse
 
+from monasca_api.common.rest import utils as rest_utils
 from monasca_api import conf
 from monasca_api.v2.common.exceptions import HTTPUnprocessableEntityError
-from monasca_common.rest import utils as rest_utils
 from monasca_common.validation import metrics as metric_validation
 
 
diff --git a/requirements.txt b/requirements.txt
index 122412885..a89ae871c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -24,3 +24,4 @@ voluptuous>=0.8.9 # BSD License
 eventlet!=0.18.3,!=0.20.1,!=0.21.0,!=0.23.0,!=0.25.0,>=0.18.2 # MIT
 monasca-common>=2.16.0 # Apache-2.0
 SQLAlchemy!=1.1.5,!=1.1.6,!=1.1.7,!=1.1.8,>=1.0.10 # MIT
+simplejson>=3.8.1 # MIT