[dogstatsd] Allow to dynamically use default route as a statsd host

When you run in a containerized environment, the dogstatsd server will
likely expose its port on the host network. If you have an application
that runs within a container, it needs to connect to it using the
default route.

Author: Remi Hakim

datadog/__init__.py

@@ -35,7 +35,7 @@
 
 
 def initialize(api_key=None, app_key=None, host_name=None, api_host=None,
-               statsd_host=None, statsd_port=None, **kwargs):
+               statsd_host=None, statsd_port=None, statsd_use_default_route=False, **kwargs):
     """
     Initialize and configure Datadog.api and Datadog.statsd modules
 
@@ -57,6 +57,10 @@ def initialize(api_key=None, app_key=None, host_name=None, api_host=None,
     :param statsd_port: Port of DogStatsd server or statsd daemon
     :type statsd_port: port
 
+    :param statsd_use_default_route: Dynamically set the statsd host to the default route
+    (Useful when running the client in a container)
+    :type statsd_use_default_route: boolean
+
     :param cacert: Path to local certificate file used to verify SSL \
         certificates. Can also be set to True (default) to use the systems \
         certificate store, or False to skip SSL verification
@@ -74,10 +78,15 @@ def initialize(api_key=None, app_key=None, host_name=None, api_host=None,
         os.environ.get('DATADOG_HOST', 'https://app.datadoghq.com')
 
     # Statsd configuration -overrides default statsd instance attributes-
-    if statsd_host and statsd_port:
+    if statsd_host:
         statsd.host = statsd_host
+
+    if statsd_port:
         statsd.port = int(statsd_port)
 
+    if statsd_use_default_route:
+        statsd.use_default_route = statsd_use_default_route
+
     # HTTP client and API options
     for key, value in iteritems(kwargs):
         attribute = "_{0}".format(key)

datadog/dogstatsd/base.py

@@ -8,6 +8,7 @@
 from random import random
 from time import time
 import socket
+import struct
 from functools import wraps
 
 try:
@@ -23,7 +24,7 @@ class DogStatsd(object):
     OK, WARNING, CRITICAL, UNKNOWN = (0, 1, 2, 3)
 
     def __init__(self, host='localhost', port=8125, max_buffer_size=50, namespace=None,
-                 constant_tags=None, use_ms=False):
+                 constant_tags=None, use_ms=False, use_default_route=False):
         """
         Initialize a DogStatsd object.
 
@@ -50,6 +51,11 @@ def __init__(self, host='localhost', port=8125, max_buffer_size=50, namespace=No
 
         :envvar DATADOG_TAGS: Tags to attach to every metric reported by dogstatsd client
         :type constant_tags: list of strings
+
+        :param use_default_route: Dynamically set the statsd host to the default route
+        (Useful when running the client in a container)
+        :type use_default_route: boolean
+
         """
         self.host = host
         self.port = int(port)
@@ -63,6 +69,9 @@ def __init__(self, host='localhost', port=8125, max_buffer_size=50, namespace=No
         self.constant_tags = constant_tags + env_tags
         self.namespace = namespace
         self.use_ms = use_ms
+        self.use_default_route = use_default_route
+        if self.use_default_route:
+            self.host = self._get_default_route()
 
     def __enter__(self):
         self.open_buffer(self.max_buffer_size)
@@ -71,6 +80,18 @@ def __enter__(self):
     def __exit__(self, type, value, traceback):
         self.close_buffer()
 
+    def _get_default_route(self):
+        try:
+            with open('/proc/net/route') as f:
+                for line in f.readlines():
+                    fields = line.strip().split()
+                    if fields[1] == '00000000':
+                        return socket.inet_ntoa(struct.pack('<L', int(fields[2], 16)))
+        except IOError as e:
+            log.error('Unable to open /proc/net/route: %s', e)
+
+        return None
+
     def get_socket(self):
         """
         Return a connected socket.
@@ -79,6 +100,9 @@ def get_socket(self):
         avoid bad thread race conditions.
         """
         if not self.socket:
+            if self.use_default_route:
+                self.host = self._get_default_route()
+
             sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
             sock.connect((self.host, self.port))
             self.socket = sock

tests/unit/dogstatsd/test_statsd.py

@@ -65,6 +65,14 @@ def test_initialization(self):
         t.assert_equal(statsd.host, "myhost")
         t.assert_equal(statsd.port, 1234)
 
+    def test_default_route(self):
+        options = {
+            'statsd_use_default_route': True,
+        }
+
+        initialize(**options)
+        t.assert_equal(statsd.use_default_route, True)
+
     def test_set(self):
         self.statsd.set('set', 123)
         assert self.recv() == 'set:123|s'