Raise exception when failed to get discovery_url

If discovery endpoint is not accessible, magnum returns "ERROR: Timed
out waiting for a reply to message ID a74fe7ec63b34f298c46c9f6659257d7
(HTTP 500)" when we create a bay. The response is misleading.
So we should raise exception when magnum fails to get discovery_url
and make the response easy to understand.

Change-Id: Ia649e55de0878160f42fecf1647d9da7fc954d72
Closes-Bug: #1529200

magnum/common/exception.py

@@ -283,6 +283,10 @@ class InvalidDiscoveryURL(Invalid):
                 "discovery endpoint '%(discovery_endpoint)s'.")
 
 
+class GetDiscoveryUrlFailed(MagnumException):
+    message = _("Fail to get discovery url from %(discovery_endpoint)")
+
+
 class InvalidUuidOrName(Invalid):
     message = _("Expected a name or uuid but received %(uuid)s.")
 

magnum/conductor/template_definition.py

@@ -375,7 +375,12 @@ class BaseTemplateDefinition(TemplateDefinition):
             discovery_endpoint = (
                 cfg.CONF.bay.etcd_discovery_service_endpoint_format %
                 {'size': bay.master_count})
-            discovery_url = requests.get(discovery_endpoint).text
+            try:
+                discovery_url = requests.get(discovery_endpoint).text
+            except Exception as err:
+                LOG.error(six.text_type(err))
+                raise exception.GetDiscoveryUrlFailed(
+                    discovery_endpoint=discovery_endpoint)
             if not discovery_url:
                 raise exception.InvalidDiscoveryURL(
                     discovery_url=discovery_url,

magnum/tests/unit/conductor/test_template_definition.py

@@ -288,6 +288,21 @@ class AtomicK8sTemplateDefinitionTestCase(base.TestCase):
         self.assertEqual(expected_discovery_url, mock_bay.discovery_url)
         self.assertEqual(expected_discovery_url, discovery_url)
 
+    @mock.patch('requests.get')
+    def test_k8s_get_discovery_url_fail(self, mock_get):
+        cfg.CONF.set_override('etcd_discovery_service_endpoint_format',
+                              'http://etcd/test?size=%(size)d',
+                              group='bay')
+        mock_get.side_effect = Exception()
+        mock_bay = mock.MagicMock()
+        mock_bay.master_count = 10
+        mock_bay.discovery_url = None
+
+        k8s_def = tdef.AtomicK8sTemplateDefinition()
+
+        self.assertRaises(exception.GetDiscoveryUrlFailed,
+                          k8s_def.get_discovery_url, mock_bay)
+
     def test_k8s_get_heat_param(self):
         k8s_def = tdef.AtomicK8sTemplateDefinition()