wsgi: Add keepalive_timeout option

Clients sometimes hold open connections "just in case" they might later
pipeline requests. This can cause issues for proxies, especially if
operators restrict max_clients in an effort to improve response times
for the requests that *do* get serviced.

Add a new keepalive_timeout option to give proxies a way to drop these
established-but-idle connections without impacting active connections
(as may happen when reducing client_timeout). Note that this requires
eventlet 0.33.4 or later.

Change-Id: Ib5bb84fa3f8a4b9c062d58c8d3689e7030d9feb3

etc/proxy-server.conf-sample

@@ -85,8 +85,14 @@ bind_port = 8080
 # CORS documentation).
 # cors_expose_headers =
 #
+# General timeout when sending to or receiving from clients.
 # client_timeout = 60.0
 #
+# Timeout to use when looking for pipelined requests. Set to zero to disable
+# request pipelining. Defaults to client_timeout. Requires eventlet>=0.33.4;
+# with earlier eventlet, any non-zero value is treated as client_timeout.
+# keepalive_timeout =
+#
 # Note: enabling evenlet_debug might reveal sensitive information, for example
 # signatures for temp urls
 # eventlet_debug = false

swift/common/wsgi.py

@@ -434,6 +434,9 @@ def run_server(conf, logger, sock, global_conf=None, ready_callback=None,
         # header; "Etag" just won't do).
         'capitalize_response_headers': False,
     }
+    if conf.get('keepalive_timeout'):
+        server_kwargs['keepalive'] = float(conf['keepalive_timeout']) or False
+
     if ready_callback:
         ready_callback()
     # Yes, eventlet, we know -- we have to support bad clients, though

test/unit/common/test_wsgi.py

@@ -496,6 +496,7 @@ class TestWSGI(unittest.TestCase):
         config = """
         [DEFAULT]
         client_timeout = 30
+        keepalive_timeout = 10
         max_clients = 1000
         swift_dir = TEMPDIR
 
@@ -535,6 +536,7 @@ class TestWSGI(unittest.TestCase):
         self.assertTrue('custom_pool' in kwargs)
         self.assertEqual(1000, kwargs['custom_pool'].size)
         self.assertEqual(30, kwargs['socket_timeout'])
+        self.assertEqual(10, kwargs['keepalive'])
 
         proto_class = kwargs['protocol']
         self.assertEqual(proto_class, wsgi.SwiftHttpProtocol)
@@ -585,6 +587,7 @@ class TestWSGI(unittest.TestCase):
         self.assertTrue('custom_pool' in kwargs)
         self.assertEqual(10, kwargs['custom_pool'].size)
         self.assertEqual(2.5, kwargs['socket_timeout'])
+        self.assertNotIn('keepalive', kwargs)  # eventlet defaults to True
 
         proto_class = kwargs['protocol']
         self.assertEqual(proto_class, wsgi.SwiftHttpProxiedProtocol)
@@ -594,6 +597,7 @@ class TestWSGI(unittest.TestCase):
         config = """
         [DEFAULT]
         swift_dir = TEMPDIR
+        keepalive_timeout = 0
 
         [pipeline:main]
         pipeline = proxy-server
@@ -623,6 +627,7 @@ class TestWSGI(unittest.TestCase):
         self.assertTrue('protocol' in kwargs)
         self.assertEqual('HTTP/1.0',
                          kwargs['protocol'].default_request_version)
+        self.assertIs(False, kwargs['keepalive'])
 
     def test_run_server_conf_dir(self):
         config_dir = {