Eventlet green threads not released back to pool

Presently, the wsgi server allows persist connections hence even after
the response is sent to the client, it doesn't close the client socket
connection.
Because of this problem, the green thread is not released back to the pool.

In order to close the client socket connection explicitly after the
response is sent and read successfully by the client, you simply have to
set keepalive to False when you create a wsgi server.

DocImpact:
Added wsgi_keep_alive option (default=True).
In order to maintain the backward compatibility, setting wsgi_keep_alive
as True by default. Recommended is set it to False.

SecurityImpact

Closes-Bug: #1361360
Change-Id: Ic57b2aceb136e8626388cfe4df72b2f47cb0661c

cinder/wsgi.py

@@ -84,6 +84,11 @@ eventlet_opts = [
                     "If an incoming connection is idle for this number of "
                     "seconds it will be closed. A value of \'0\' means "
                     "wait forever."),
+    cfg.BoolOpt('wsgi_keep_alive',
+                default=True,
+                help='If False, closes the client socket connection '
+                     'explicitly. Setting it to True to maintain backward '
+                     'compatibility. Recommended setting is set it to False.'),
 ]
 
 CONF = cfg.CONF
@@ -236,7 +241,8 @@ class Server(object):
             'protocol': self._protocol,
             'custom_pool': self._pool,
             'log': self._wsgi_logger,
-            'socket_timeout': self.client_socket_timeout
+            'socket_timeout': self.client_socket_timeout,
+            'keepalive': CONF.wsgi_keep_alive
         }
 
         self._server = eventlet.spawn(**wsgi_kwargs)

etc/cinder/cinder.conf.sample

@@ -311,6 +311,11 @@
 # value)
 #client_socket_timeout=900
 
+# If False, closes the client socket connection explicitly.
+# Setting it to True to maintain backward compatibility.
+# Recommended setting is set it to False. (boolean value)
+#wsgi_keep_alive=true
+
 # Sets the value of TCP_KEEPALIVE (True/False) for each server
 # socket. (boolean value)
 #tcp_keepalive=true