Add a timeout to azure meta data service (#939)

Author: lzchen

contrib/opencensus-ext-azure/opencensus/ext/azure/metrics_exporter/heartbeat_metrics/heartbeat.py

@@ -100,8 +100,9 @@ def get_azure_compute_metadata(self):
         try:
             request_url = "{0}?{1}&{2}".format(
                 _AIMS_URI, _AIMS_API_VERSION, _AIMS_FORMAT)
-            response = requests.get(request_url, headers={"MetaData": "True"})
-        except requests.exceptions.ConnectionError:
+            response = requests.get(
+                request_url, headers={"MetaData": "True"}, timeout=5.0)
+        except (requests.exceptions.ConnectionError, requests.Timeout):
             # Not in VM
             self.is_vm = False
             return False

contrib/opencensus-ext-azure/tests/test_azure_heartbeat_metrics.py

@@ -218,6 +218,17 @@ def test_heartbeat_metric_not_vm(self):
             keys = list(metric.properties.keys())
             self.assertEqual(len(keys), 2)
 
+    def test_heartbeat_metric_not_vm_timeout(self):
+        with mock.patch(
+            'requests.get',
+            throw(requests.Timeout)
+        ):
+            metric = heartbeat_metrics.HeartbeatMetric()
+            self.assertFalse(metric.is_vm)
+            self.assertEqual(metric.NAME, 'Heartbeat')
+            keys = list(metric.properties.keys())
+            self.assertEqual(len(keys), 2)
+
     def test_heartbeat_metric_vm_error_response(self):
         with mock.patch('requests.get') as get:
             get.return_value = MockResponse(