diff --git a/.zuul.yaml b/.zuul.yaml
index 369087cba7..b06e5ac96f 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -1,4 +1,5 @@
 - project:
+    queue: sahara
     templates:
       - openstack-python3-zed-jobs
       - periodic-stable-jobs
@@ -22,7 +23,6 @@
         - openstack-ansible-deploy-aio_sahara_metal-ubuntu-focal:
             voting: false
     gate:
-      queue: sahara
       jobs:
         - sahara-tests-scenario:
             voting: false
diff --git a/sahara/tests/unit/utils/test_api_validator.py b/sahara/tests/unit/utils/test_api_validator.py
index 1ea21e65fb..23828647cf 100644
--- a/sahara/tests/unit/utils/test_api_validator.py
+++ b/sahara/tests/unit/utils/test_api_validator.py
@@ -259,7 +259,7 @@ class ApiValidatorTest(testtools.TestCase):
     def test_validate_hostname(self):
         schema = {
             "type": "string",
-            "format": "hostname",
+            "format": "idn-hostname",
         }
 
         self._validate_success(schema, "abcd")
diff --git a/sahara/utils/api_validator.py b/sahara/utils/api_validator.py
index ec3174f94a..558110d483 100644
--- a/sahara/utils/api_validator.py
+++ b/sahara/utils/api_validator.py
@@ -97,85 +97,70 @@ def validate_posix_path(entry):
     return res is not None
 
 
-class ConfigTypeMeta(type):
-    def __instancecheck__(cls, instance):
-        # configs should be dict
-        if not isinstance(instance, dict):
+def is_config(cls, instance):
+    # configs should be dict
+    if not isinstance(instance, dict):
+        return False
+
+    # check dict content
+    for applicable_target, configs in six.iteritems(instance):
+        # upper-level dict keys (applicable targets) should be strings
+        if not isinstance(applicable_target, six.string_types):
             return False
 
-        # check dict content
-        for applicable_target, configs in six.iteritems(instance):
-            # upper-level dict keys (applicable targets) should be strings
-            if not isinstance(applicable_target, six.string_types):
-                return False
-
-            # upper-level dict values should be dicts
-            if not isinstance(configs, dict):
-                return False
-
-            # check internal dict content
-            for config_name, config_value in six.iteritems(configs):
-                # internal dict keys should be strings
-                if not isinstance(config_name, six.string_types):
-                    return False
-
-                # internal dict values should be strings or integers or bools
-                if not isinstance(config_value,
-                                  (six.string_types, six.integer_types)):
-                    return False
-
-        return True
-
-
-class SimpleConfigTypeMeta(type):
-    def __instancecheck__(cls, instance):
-        # configs should be dict
-        if not isinstance(instance, dict):
+        # upper-level dict values should be dicts
+        if not isinstance(configs, dict):
             return False
 
-        # check dict content
-        for conf_name, conf_value in six.iteritems(instance):
-            # keys should be strings, values should be int, string or bool
-            if not isinstance(conf_name, six.string_types):
+        # check internal dict content
+        for config_name, config_value in six.iteritems(configs):
+            # internal dict keys should be strings
+            if not isinstance(config_name, six.string_types):
                 return False
-            if not isinstance(conf_value,
+
+            # internal dict values should be strings or integers or bools
+            if not isinstance(config_value,
                               (six.string_types, six.integer_types)):
                 return False
-        return True
+
+    return True
 
 
-@six.add_metaclass(ConfigTypeMeta)
-class ConfigsType(dict):
-    pass
+def is_simple_config(cls, instance):
+    # configs should be dict
+    if not isinstance(instance, dict):
+        return False
+
+    # check dict content
+    for conf_name, conf_value in six.iteritems(instance):
+        # keys should be strings, values should be int, string or bool
+        if not isinstance(conf_name, six.string_types):
+            return False
+        if not isinstance(conf_value,
+                          (six.string_types, six.integer_types)):
+            return False
+    return True
 
 
-@six.add_metaclass(SimpleConfigTypeMeta)
-class SimpleConfigsType(dict):
-    pass
-
-
-class FlavorTypeMeta(type):
-    def __instancecheck__(cls, instance):
-        try:
-            int(instance)
-        except (ValueError, TypeError):
-            return (isinstance(instance, six.string_types)
-                    and uuidutils.is_uuid_like(instance))
-        return (isinstance(instance, six.integer_types + six.string_types)
-                and type(instance) != bool)
-
-
-@six.add_metaclass(FlavorTypeMeta)
-class FlavorType(object):
-    pass
+def is_flavor_type(cls, instance):
+    try:
+        int(instance)
+    except (ValueError, TypeError):
+        return (isinstance(instance, six.string_types)
+                and uuidutils.is_uuid_like(instance))
+    return (isinstance(instance, six.integer_types + six.string_types)
+            and type(instance) != bool)
 
 
 class ApiValidator(jsonschema.Draft4Validator):
-    def __init__(self, schema):
-        format_checker = jsonschema.FormatChecker()
+
+    TYPE_CHECKER = jsonschema.Draft4Validator.TYPE_CHECKER.redefine_many({
+        "configs": is_config,
+        "flavor": is_flavor_type,
+        "simple_config": is_simple_config,
+    })
+
+    def __init__(self, schema, resolver=None,
+                 format_checker=jsonschema.FormatChecker()):
         super(ApiValidator, self).__init__(
-            schema, format_checker=format_checker, types={
-                "configs": ConfigsType,
-                "flavor": FlavorType,
-                "simple_config": SimpleConfigsType,
-            })
+            schema, format_checker=format_checker)
diff --git a/sahara/utils/openstack/images.py b/sahara/utils/openstack/images.py
index efa162b0a9..e5267261e5 100644
--- a/sahara/utils/openstack/images.py
+++ b/sahara/utils/openstack/images.py
@@ -50,7 +50,7 @@ def wrap_entity(func):
 
 def _get_all_tags(image_props):
     tags = []
-    for key, value in image_props.iteritems():
+    for key, value in six.iteritems(image_props):
         if key.startswith(PROP_TAG) and value:
             tags.append(key)
     return tags
@@ -69,7 +69,7 @@ def _parse_tags(image_props):
 
 def _serialize_metadata(image):
     data = {}
-    for key, value in image.iteritems():
+    for key, value in six.iteritems(image):
         if key.startswith('_sahara') and value:
             data[key] = value
     return data