More gracefully handle errors loading service config

If we can't load service config, we'll loudly log it and then replace
the application with one which responds to all requests with HTTP 503
Service Unavailable.

Equivalent of cloudendpoints/endpoints-management-java#39

Author: inklesspen

endpoints_management/config/__init__.py

@@ -11,3 +11,7 @@
 # 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 __future__ import absolute_import
+
+from .service_config import ServiceConfigException

endpoints_management/config/service_config.py

@@ -39,6 +39,10 @@
 _SERVICE_VERSION_ENV_KEY = u"ENDPOINTS_SERVICE_VERSION"
 
 
+class ServiceConfigException(Exception):
+    pass
+
+
 def fetch_service_config(service_name=None, service_version=None):
     """Fetches the service config from Google Serivce Management API.
 
@@ -76,7 +80,7 @@ def fetch_service_config(service_name=None, service_version=None):
     status_code = response.status
     if status_code != 200:
         message_template = u"Fetching service config failed (status code {})"
-        _log_and_raise(Exception, message_template.format(status_code))
+        _log_and_raise(ServiceConfigException, message_template.format(status_code))
 
     logger.debug(u'obtained service json from the management api:\n%s', response.data)
     service = encoding.JsonToMessage(messages.Service, response.data)

endpoints_management/control/service.py

@@ -37,8 +37,8 @@
 from apitools.base.py import encoding
 from enum import Enum
 
+from ..config import service_config
 from . import label_descriptor, metric_descriptor, path_regex, sm_messages
-from endpoints_management.config import service_config
 
 
 logger = logging.getLogger(__name__)

endpoints_management/control/wsgi.py

@@ -33,8 +33,10 @@
 import urllib2
 import urlparse
 import wsgiref.util
+from webob.exc import HTTPServiceUnavailable
 
 from ..auth import suppliers, tokens
+from ..config.service_config import ServiceConfigException
 from . import check_request, quota_request, report_request, service, sm_messages
 
 
@@ -118,9 +120,14 @@ def add_all(application, project_id, control_client,
        loader (:class:`endpoints_management.control.service.Loader`): loads the service
           instance that configures this instance's behaviour
     """
-    a_service = loader.load()
-    if not a_service:
-        raise ValueError(u"Failed to load service config")
+    try:
+        a_service = loader.load()
+        if not a_service:
+            raise ValueError(u'No service config loaded.')
+    except (ServiceConfigException, ValueError):
+        logger.exception(u'Failed to load service config, installing server error handler.')
+        # This will answer all requests with HTTP 503 Service Unavailable
+        return HTTPServiceUnavailable
     authenticator = _create_authenticator(a_service)
 
     wrapped_app = Middleware(application, project_id, control_client)

requirements.txt

@@ -8,3 +8,4 @@ pyjwkest>=1.0.0,<=1.0.9
 requests>=2.10.0,<3.0
 strict-rfc3339>=0.7,<0.8
 urllib3>=1.16,<2.0
+webob>=1.7.4

setup.py

@@ -40,6 +40,7 @@
     "requests>=2.10.0,<3.0",
     'strict-rfc3339>=0.7,<0.8',
     'urllib3>=1.16,<2.0',
+    'webob>=1.7.4',
 ]
 
 tests_require = [

test/test_service_config.py

@@ -88,7 +88,7 @@ def test_fetch_service_config_failed(self):
         mock_http_client = mock.MagicMock()
         mock_http_client.request.return_value = mock_response
         ServiceConfigFetchTest._get_http_client.return_value = mock_http_client
-        with self.assertRaisesRegexp(Exception, u"status code 403"):
+        with self.assertRaisesRegexp(service_config.ServiceConfigException, u"status code 403"):
             service_config.fetch_service_config()
 
     @mock.patch(u"endpoints_management.config.service_config.client.GoogleCredentials",

test/test_wsgi.py

@@ -134,11 +134,11 @@ def test_should_send_report_request_if_check_fails(self):
 
     def test_load_service_failed(self):
         loader = mock.MagicMock(load=lambda: None)
-        with self.assertRaisesRegex(ValueError, u"Failed to load service config"):
-            wsgi.add_all(_DummyWsgiApp(),
-                         self.PROJECT_ID,
-                         mock.MagicMock(spec=client.Client),
-                         loader=loader)
+        result = wsgi.add_all(_DummyWsgiApp(),
+                              self.PROJECT_ID,
+                              mock.MagicMock(spec=client.Client),
+                              loader=loader)
+        assert result is wsgi.HTTPServiceUnavailable
 
 
 _SYSTEM_PARAMETER_CONFIG_TEST = b"""