Treat any statsd metric driver related errors as non-fatal (just log the errors)

CHANGELOG.rst

@@ -59,8 +59,17 @@ Fixed
 * Make sure we don't log auth token and api key inside st2api log file if those values are provided
   via query parameter and not header (``?x-auth-token=foo``, ``?st2-api-key=bar``). (bug fix) #4592
   #4589
-* Fix rendering of config_context in orquesta task that references action in different pack 
+* Fix rendering of config_context in orquesta task that references action in different pack.
   (bug fix) #4570
+* Add missing default config location (``/etc/st2/st2.conf``) to the following services:
+  ``st2actionrunner``, ``st2scheduler``, ``st2workflowengine``. (bug fix) #4596
+* Update statsd metrics driver so any exception thrown by statsd library is treated as non fatal.
+
+  Previously there was an edge case if user used a hostname instead of an IP address for metrics
+  backend server address. In such scenario, if hostname DNS resolution failed, statsd driver would
+  throw the exception which would propagate all the way up and break the application. (bug fix) #4597
+
+  Reported by Chris McKenzie.
 
 2.10.3 - March 06, 2019
 -----------------------

st2common/st2common/metrics/drivers/statsd_driver.py

@@ -13,14 +13,28 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import socket
+import logging as stdlib_logging
 from numbers import Number
 
 import statsd
 from oslo_config import cfg
 
+from st2common import log as logging
 from st2common.metrics.base import BaseMetricsDriver
 from st2common.metrics.utils import check_key
 from st2common.metrics.utils import get_full_key_name
+from st2common.util.misc import ignore_and_log_exception
+
+
+LOG = logging.getLogger(__name__)
+
+# Which exceptions thrown by statsd library should be considered as non-fatal
+NON_FATAL_EXC_CLASSES = [
+    socket.error,
+    IOError,
+    OSError
+]
 
 __all__ = [
     'StatsdDriver'
@@ -30,11 +44,22 @@
 class StatsdDriver(BaseMetricsDriver):
     """
     StatsD Implementation of the metrics driver
+
+    NOTE: Statsd uses UDP which is "fire and forget" and any kind of send error is not fatal. There
+    is an issue with python-statsd library though which doesn't ignore DNS resolution related errors
+    and bubbles them all the way up.
+
+    This of course breaks the application. Any kind of metric related errors should be considered
+    as non-fatal and not degrade application in any way if an error occurs. That's why we wrap all
+    the statsd library calls here to ignore the errors and just log them.
     """
+
     def __init__(self):
         statsd.Connection.set_defaults(host=cfg.CONF.metrics.host, port=cfg.CONF.metrics.port,
                                        sample_rate=cfg.CONF.metrics.sample_rate)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def time(self, key, time):
         """
         Timer metric
@@ -46,6 +71,8 @@ def time(self, key, time):
         timer = statsd.Timer('')
         timer.send(key, time)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def inc_counter(self, key, amount=1):
         """
         Increment counter
@@ -57,6 +84,8 @@ def inc_counter(self, key, amount=1):
         counter = statsd.Counter(key)
         counter.increment(delta=amount)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def dec_counter(self, key, amount=1):
         """
         Decrement metric
@@ -68,6 +97,8 @@ def dec_counter(self, key, amount=1):
         counter = statsd.Counter(key)
         counter.decrement(delta=amount)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def set_gauge(self, key, value):
         """
         Set gauge value.
@@ -79,6 +110,8 @@ def set_gauge(self, key, value):
         gauge = statsd.Gauge(key)
         gauge.send(None, value)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def inc_gauge(self, key, amount=1):
         """
         Increment gauge value.
@@ -90,6 +123,8 @@ def inc_gauge(self, key, amount=1):
         gauge = statsd.Gauge(key)
         gauge.increment(None, amount)
 
+    @ignore_and_log_exception(exc_classes=NON_FATAL_EXC_CLASSES, logger=LOG,
+                              level=stdlib_logging.WARNING)
     def dec_gauge(self, key, amount=1):
         """
         Decrement gauge value.

st2common/st2common/util/misc.py

@@ -15,18 +15,22 @@
 
 from __future__ import absolute_import
 
+import logging
+
 import os
 import re
 import sys
 import collections
+import functools
 
 import six
 
 __all__ = [
     'prefix_dict_keys',
     'compare_path_file_name',
     'lowercase_value',
-    'get_field_name_from_mongoengine_error'
+    'get_field_name_from_mongoengine_error',
+
 ]
 
 
@@ -168,3 +172,28 @@ def get_field_name_from_mongoengine_error(exc):
         return match.groups()[0]
 
     return msg
+
+
+def ignore_and_log_exception(exc_classes=(Exception,), logger=None, level=logging.WARNING):
+    """
+    Decorator which catches the provided exception classes and logs them instead of letting them
+    bubble all the way up.
+    """
+    exc_classes = tuple(exc_classes)
+
+    def decorator(func):
+        @functools.wraps(func)
+        def wrapper(*args, **kwargs):
+            try:
+                return func(*args, **kwargs)
+            except exc_classes as e:
+                if len(args) >= 1 and getattr(args[0], '__class__', None):
+                    func_name = '%s.%s' % (args[0].__class__.__name__, func.__name__)
+                else:
+                    func_name = func.__name__
+
+                message = ('Exception in fuction "%s": %s' % (func_name, str(e)))
+                logger.log(level, message)
+
+        return wrapper
+    return decorator

st2common/tests/unit/test_metrics.py

@@ -12,9 +12,13 @@
 # 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 datetime import datetime, timedelta
+
+import socket
+from datetime import datetime
+from datetime import timedelta
 
 import unittest2
+import mock
 from mock import patch, MagicMock
 
 from oslo_config import cfg
@@ -200,6 +204,52 @@ def test_get_full_key_name(self):
         result = get_full_key_name('api.requests')
         self.assertEqual(result, 'st2.prod.api.requests')
 
+    @patch('st2common.metrics.drivers.statsd_driver.LOG')
+    @patch('st2common.metrics.drivers.statsd_driver.statsd')
+    def test_driver_socket_exceptions_are_not_fatal(self, statsd, mock_log):
+        # Socket errors such as DNS resolution errors should be considered non fatal and ignored
+        mock_logger = mock.Mock()
+        StatsdDriver.logger = mock_logger
+
+        # 1. timer
+        mock_timer = MagicMock(side_effect=socket.error('error 1'))
+        statsd.Timer('').send.side_effect = mock_timer
+        params = ('test', 10)
+        self._driver.time(*params)
+        statsd.Timer('').send.assert_called_with('st2.test', 10)
+
+        # 2. counter
+        key = 'test'
+        mock_counter = MagicMock(side_effect=socket.error('error 2'))
+        statsd.Counter(key).increment.side_effect = mock_counter
+        self._driver.inc_counter(key)
+        mock_counter.assert_called_once_with(delta=1)
+
+        key = 'test'
+        mock_counter = MagicMock(side_effect=socket.error('error 3'))
+        statsd.Counter(key).decrement.side_effect = mock_counter
+        self._driver.dec_counter(key)
+        mock_counter.assert_called_once_with(delta=1)
+
+        # 3. gauge
+        params = ('key', 100)
+        mock_gauge = MagicMock(side_effect=socket.error('error 4'))
+        statsd.Gauge().send.side_effect = mock_gauge
+        self._driver.set_gauge(*params)
+        mock_gauge.assert_called_once_with(None, params[1])
+
+        params = ('key1',)
+        mock_gauge = MagicMock(side_effect=socket.error('error 5'))
+        statsd.Gauge().increment.side_effect = mock_gauge
+        self._driver.inc_gauge(*params)
+        mock_gauge.assert_called_once_with(None, 1)
+
+        params = ('key1',)
+        mock_gauge = MagicMock(side_effect=socket.error('error 6'))
+        statsd.Gauge().decrement.side_effect = mock_gauge
+        self._driver.dec_gauge(*params)
+        mock_gauge.assert_called_once_with(None, 1)
+
 
 class TestCounterContextManager(unittest2.TestCase):
     @patch('st2common.metrics.base.METRICS')