Upload basic info about completed swarming tasks to event_mon

appengine/swarming/event_mon_metrics.py

+# Copyright 2016 The LUCI Authors. All rights reserved.
+# Use of this source code is governed under the Apache License, Version 2.0
+# that can be found in the LICENSE file.
+
+import logging
+
+import gae_event_mon
+
+
+def initialize():
+  gae_event_mon.initialize('swarming')
+
+
+def send_task_event(task_result_summary):
+  """Sends an event_mon event about a swarming task.

[M-A Ruel, 2016/11/28 16:56:32]

Is this synchronous or asynchronous? Please specify.

[Paweł Hajdan Jr., 2016/11/29 14:37:33]

Done. Ideally we'd have an async mode available, but as far as I know that's not
the case yet.

[M-A Ruel, 2016/11/29 14:48:40]

Ok then can you document what are the side effects? Is it an urlfetch, is it a
DB write?

[Paweł Hajdan Jr., 2016/11/29 15:14:17]

Done. Please note this comment might get out of sync with future implementation
of gae_event_mon.

+
+  Args:
+    task_result_summary: TaskResultSummary object.
+  """
+  event = gae_event_mon.Event('POINT')
+  event.proto.swarming_task_event.id = task_result_summary.task_id
+  logging.info('Sending event: %s', event.proto)
+  event.send()

[Vadim Sh., 2016/11/28 19:19:31]

should we wrap this in try: except: and log errors instead of failing? Otherwise
an outage of monitoring pipeline would cause a Swarming outage.

[Paweł Hajdan Jr., 2016/11/29 14:37:33]

Good point. Done. Marc-Antoine, what do you think?

I'm somewhat worried about possible silent failures because of this. Compared to
a complete swarming outage it may be a reasonable tradeoff.