use 0.0.0.0 as server address when non_local_traffic is passed (#2691)

dogstatsd.py

@@ -484,6 +484,7 @@ def init(config_path=None, use_watchdog=False, use_forwarder=False, args=None):
     forward_to_port = c.get('statsd_forward_port')
     event_chunk_size = c.get('event_chunk_size')
     recent_point_threshold = c.get('recent_point_threshold', None)
+    server_host = c['bind_host']
 
     target = c['dd_url']
     if use_forwarder:
@@ -508,12 +509,14 @@ def init(config_path=None, use_watchdog=False, use_forwarder=False, args=None):
     # Start the reporting thread.
     reporter = Reporter(interval, aggregator, target, api_key, use_watchdog, event_chunk_size)
 
-    # Start the server on an IPv4 stack
-    # Default to loopback
-    server_host = c['bind_host']
-    # If specified, bind to all addressses
+    # NOTICE: when `non_local_traffic` is passed we need to bind to any interface on the box. The forwarder uses
+    # Tornado which takes care of sockets creation (more than one socket can be used at once depending on the
+    # network settings), so it's enough to just pass an empty string '' to the library.
+    # In Dogstatsd we use a single, fullstack socket, so passing '' as the address doesn't work and we default to
+    # '0.0.0.0'. If someone needs to bind Dogstatsd to the IPv6 '::', they need to turn off `non_local_traffic` and
+    # use the '::' meta address as `bind_host`.
     if non_local_traffic:
-        server_host = ''
+        server_host = '0.0.0.0'
 
     server = Server(aggregator, server_host, port, forward_to_host=forward_to_host, forward_to_port=forward_to_port)
 

tests/core/test_dogstatsd.py

@@ -3,13 +3,14 @@
 import socket
 import threading
 import Queue
+from collections import defaultdict
 
 # 3p
 import mock
 
 # project
 from dogstatsd import mapto_v6, get_socket_address
-from dogstatsd import Server
+from dogstatsd import Server, init
 from utils.net import IPV6_V6ONLY, IPPROTO_IPV6
 
 
@@ -29,6 +30,20 @@ def test_get_socket_address(self):
             self.assertEqual(get_socket_address('example.com', 80), ('::1', 80, 0, 0))
         self.assertIsNone(get_socket_address('foo', 80))
 
+    @mock.patch('dogstatsd.get_config')
+    @mock.patch('dogstatsd.Server')
+    def test_init(self, s, gc):
+        gc.return_value = defaultdict(str)
+        gc.return_value['non_local_traffic'] = True
+        gc.return_value['use_dogstatsd'] = True
+
+        init()
+
+        # if non_local_traffic was passed, use IPv4 wildcard
+        s.assert_called_once()
+        args, _ = s.call_args
+        self.assertEqual(args[1], '0.0.0.0')
+
 
 class TestServer(TestCase):
     @mock.patch('dogstatsd.get_socket_address')