Add option to set SO_KEEPALIVE on listener socket

Closes #3115

THANKS

@@ -37,6 +37,7 @@ Brett Randall <[email protected]>
 Brian Rosner <[email protected]>
 Bruno Bigras <[email protected]>
 Caleb Brown <[email protected]>
+Cédric Krier <[email protected]>
 Chris Adams <[email protected]>
 Chris Forbes <[email protected]>
 Chris Lamb <[email protected]>

gunicorn/config.py

@@ -208,6 +208,10 @@ def sendfile(self):
 
         return True
 
+    @property
+    def so_keepalive(self):
+        return self.settings['so_keepalive'].get()
+
     @property
     def reuse_port(self):
         return self.settings['reuse_port'].get()
@@ -1029,6 +1033,21 @@ class Sendfile(Setting):
         """
 
 
+class KeepAlive(Setting):
+    name = "so_keepalive"
+    section = "Server Mechanics"
+    cli = ["--so-keep-alive"]
+    validator = validate_bool
+    action = "store_true"
+    default = False
+
+    desc = """\
+        Set the ``SO_KEEPALIVE`` flag on the listening socket.
+
+        .. versionadded:: 21.3
+        """
+
+
 class ReusePort(Setting):
     name = "reuse_port"
     section = "Server Mechanics"

gunicorn/sock.py

@@ -39,6 +39,8 @@ def __getattr__(self, name):
 
     def set_options(self, sock, bound=False):
         sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+        if self.conf.so_keepalive and hasattr(socket, 'SO_KEEPALIVE'):
+            sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
         if (self.conf.reuse_port
                 and hasattr(socket, 'SO_REUSEPORT')):  # pragma: no cover
             try: