Add --reuse-port to make use of SO_REUSEPORT optional (#1669)

Fixes #1603

docs/source/settings.rst

@@ -428,6 +428,18 @@ to enable or disable its usage.
 .. versionchanged:: 19.6
    added support for the ``SENDFILE`` environment variable
 
+.. _reuse-port:
+
+reuse_port
+~~~~~~~~~~
+
+* ``--reuse-port``
+* ``False``
+
+Set the ``SO_REUSEPORT`` flag on the listening socket.
+
+.. versionadded:: 19.8
+
 .. _chdir:
 
 chdir

gunicorn/config.py

@@ -204,6 +204,10 @@ class Config(object):
 
         return True
 
+    @property
+    def reuse_port(self):
+        return self.settings['reuse_port'].get()
+
     @property
     def paste_global_conf(self):
         raw_global_conf = self.settings['raw_paste_global_conf'].get()
@@ -954,6 +958,21 @@ class Sendfile(Setting):
         """
 
 
+class ReusePort(Setting):
+    name = "reuse_port"
+    section = "Server Mechanics"
+    cli = ["--reuse-port"]
+    validator = validate_bool
+    action = "store_true"
+    default = False
+
+    desc = """\
+        Set the ``SO_REUSEPORT`` flag on the listening socket.
+
+        .. versionadded:: 19.8
+        """
+
+
 class Chdir(Setting):
     name = "chdir"
     section = "Server Mechanics"

gunicorn/sock.py

@@ -39,7 +39,8 @@ class BaseSocket(object):
 
     def set_options(self, sock, bound=False):
         sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
-        if hasattr(socket, 'SO_REUSEPORT'):  # pragma: no cover
+        if (self.conf.reuse_port 
+            and hasattr(socket, 'SO_REUSEPORT')):  # pragma: no cover
             try:
                 sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
             except socket.error as err: