Show executor metrics (#1096)

* Use dedicated exception class when metrics response is empty

* Add test for empty container metrics

When container metrics (`/v0/containers/<c-id>`) returns a 204 empty
response, we should still check the app metrics
(`/v0/containers/<c-id>/app`) endpoint, which may have data.

This test replicates the task metrics details test, but responds with a
204 Empty followed by a 200 OK. Without the accompanying fix, it will
fail.

* Catch empty metrics exception for container datapoints

cli/dcoscli/metrics.py

@@ -9,6 +9,11 @@
 emitter = emitting.FlatEmitter()
 
 
+class EmptyMetricsException(DCOSException):
+    def __init__(self):
+        super().__init__('No metrics found')
+
+
 def _gib(n):
     return n * pow(2, -30)
 
@@ -30,7 +35,7 @@ def _fetch_metrics_datapoints(url):
     with contextlib.closing(http.get(url)) as r:
 
         if r.status_code == 204:
-            raise DCOSException('No metrics found')
+            raise EmptyMetricsException()
 
         if r.status_code != 200:
             raise DCOSHTTPException(r)
@@ -258,8 +263,18 @@ def print_task_metrics(url, app_url, summary, json_):
     :rtype: int
     """
 
-    datapoints = _fetch_metrics_datapoints(url) + _fetch_metrics_datapoints(
-        app_url)
+    container_datapoints = []
+    app_datapoints = []
+
+    # In the case of an executor, app data may exist when
+    # container data does not.
+    try:
+        container_datapoints = _fetch_metrics_datapoints(url)
+    except EmptyMetricsException:
+        pass
+
+    app_datapoints = _fetch_metrics_datapoints(app_url)
+    datapoints = container_datapoints + app_datapoints
 
     if summary:
         if json_:

cli/tests/unit/test_task.py

@@ -175,6 +175,31 @@ def test_dcos_task_metrics_agent_details(mocked_get_config_val,
                                     'container_id')
 
 
+@patch('dcos.http.get')
+@patch('dcos.mesos.get_master')
+@patch('dcos.config.get_config_val')
+def test_dcos_task_metrics_agent_missing_container(
+    mocked_get_config_val, mocked_get_master, mocked_http_get
+):
+    mocked_get_config_val.return_value = 'http://127.0.0.1'
+
+    mock_container_response = MagicMock()
+    mock_container_response.status_code = 204
+    mock_app_response = MagicMock()
+    mock_app_response.status_code = 200
+    mocked_http_get.side_effect = [mock_container_response, mock_app_response]
+
+    mock_master = MagicMock()
+    mock_master.task = lambda _: {'slave_id': 'slave_id'}
+    mock_master.get_container_id = lambda _: {
+        'parent': {},
+        'value': 'container_id'
+    }
+    mocked_get_master.return_value = mock_master
+
+    _metrics(True, 'task_id', False)
+
+
 @patch('dcos.http.get')
 @patch('dcos.mesos.get_master')
 @patch('dcos.config.get_config_val')