Web server启动过程的关键代码如下几句：

self.pool = eventlet.GreenPool(1)
self._server = self._service.pool.spawn(self._service._run,self._application,dup_sock)
def _run(self, application, socket):"""Start a WSGI server in a new green thread."""eventlet.wsgi.server(socket, application,max_size=self.num_threads,log=LOG,keepalive=CONF.wsgi_keep_alive,log_format=CONF.wsgi_log_format,socket_timeout=self.client_socket_timeout)

这几句代码的含义是：

1 创建一个协程池

2 协程的启动函数就是_run

3 _run函数的本质是创建一个符号WSGI规范的Web Server

4 这个Web Server的WSGI Application就是传入的参数application

5 这个Web Server绑定的Socket就是传入的参数socket。

下面介绍这两个参数

一 Socket

对于一个Web Server来说，它对外首先体现的就是Server IP和Server 端口号。从编程角度来说，这两者都体现在Socket中，也就是前文所说的传入参数socket，这个传入的socket，其构造方法是如下函数：

def _get_socket(self, host, port, backlog):bind_addr = (host, port)# TODO(dims): eventlet's green dns/socket module does not actually# support IPv6 in getaddrinfo(). We need to get around this in the# future or monitor upstream for a fixtry:info = socket.getaddrinfo(bind_addr[0],bind_addr[1],socket.AF_UNSPEC,socket.SOCK_STREAM)[0]family = info[0]bind_addr = info[-1]except Exception:LOG.exception(_LE("Unable to listen on %(host)s:%(port)s"),{'host': host, 'port': port})sys.exit(1)sock = Noneretry_until = time.time() + CONF.retry_until_windowwhile not sock and time.time() < retry_until:try:sock = eventlet.listen(bind_addr,backlog=backlog,family=family)except socket.error as err:with excutils.save_and_reraise_exception() as ctxt:if err.errno == errno.EADDRINUSE:ctxt.reraise = Falseeventlet.sleep(0.1)if not sock:raise RuntimeError(_("Could not bind to %(host)s:%(port)s ""after trying for %(time)d seconds") %{'host': host,'port': port,'time': CONF.retry_until_window})sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)# sockets can hang around forever without keepalivesock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)# This option isn't available in the OS X version of eventletif hasattr(socket, 'TCP_KEEPIDLE'):sock.setsockopt(socket.IPPROTO_TCP,socket.TCP_KEEPIDLE,CONF.tcp_keepidle)return sock

代码本身就是Socket编程。需要强调的一点是host、port这两个参数，它们是在配置文件（etc/neutron.conf）中配置的，比如：

#etc/neutron.conf

#绑定web server的IP地址

bind_host=0.0.0.0

#绑定到web Server的端口号

bind_port=9696

这个配置文件表明，Web Server的IP地址是本机（bind_host=0.0.0.0）,web Server的端口号是9696（bind_port=9696）。

二 Application

对于一个符合WSGI规范的Web Server而言，除了server IP和端口外，最重要的参数就是WSGI Application了，因为WSGI Application才是真正处理HTTP请求的实体。_run函数的参数application，在Neutron启动的过程中，是靠如下函数加载的：

def _run_wsgi(app_name):app = config.load_paste_app(app_name)

短短一句话，涉及Neutron Server的RESTful API发布与处理，以及Neutron Plugins的加载。