OpenStack源码阅读1之nova-api服务启动

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本文中提到的nova/service.py 等均是指的/usr/lib/python2.6/site-packages/nova 路径下的文件，不再另行说明。

nova-api启动脚本 /usr/bin/nova-api

/usr/bin/nova-api

"""Starter script for Nova API.

Starts both the EC2 and OpenStack APIs in separate greenthreads.

"""

import eventlet

eventlet.monkey_patch(os=False)

import os

import sys

possible_topdir = os.path.normpath(os.path.join(os.path.abspath(

sys.argv[0]), os.pardir, os.pardir))

if os.path.exists(os.path.join(possible_topdir, "nova", "__init__.py")):

sys.path.insert(0, possible_topdir)

from nova import flags

from nova.openstack.common import log as logging

from nova import service

from nova import utils

if __name__ == '__main__':

flags.parse_args(sys.argv)

logging.setup("nova")

utils.monkey_patch()

launcher = service.ProcessLauncher()
for api in flags.FLAGS.enabled_apis:

server = service.WSGIService(api)

launcher.launch_server(server, workers=server.workers or 1)

launcher.wait()

launcher = service.ProcessLauncher()
查看nova/service.py
此处没有什么可以解释的，就是创建了一个launcher

flags.FLAGS.enabled_apis
查看nova/flags.py
cfg.ListOpt('enabled_apis',

default=['ec2', 'osapi_compute', 'osapi_volume', 'metadata'],

help='a list of APIs to enable by default'),

server = service.WSGIService(api)
查看nova/service.py

class WSGIService(object):

"""Provides ability to launch API from a 'paste' configuration."""

def __init__(self, name, loader=None):

"""Initialize, but do not start the WSGI server.

:param name: The name of the WSGI server given to the loader.

:param loader: Loads the WSGI application using the given name.

:returns: None

"""

self.name = name

self.manager = self._get_manager() //此处返回的是None

self.loader = loader or wsgi.Loader() //wsgi的loader，用于加载模块

self.app = self.loader.load_app(name) //加载模块，其配置文件默认使用了/etc/nova/api-paste.ini文件，加载的模块为app:标示的部分

self.host = getattr(FLAGS, '%s_listen' % name, "0.0.0.0") //此处e2c_listen、osapi_volume_listen....等配置选项是在service.py文件中注册到FLAGS的
self.port = getattr(FLAGS, '%s_listen_port' % name, 0)
self.workers = getattr(FLAGS, '%s_workers' % name, None)

self.server = wsgi.Server(name, //返回wsgi的server

self.app,

host=self.host,

port=self.port)

# Pull back actual port used

self.port = self.server.port

从上面的代码可以看出，实际上返回的server是一个wsgi的server

launcher.launch_server(server, workers=server.workers or 1)
launch_server 中调用了 self._start_child(wrap)
_start_child 中调用了 self._child_process(wrap.server)

_child_process中调用了 launcher = Launcher() launcher.run_server(server)
在Launcher类的run_server 方法中调用了 server.start() server.wait()
上面的方法实际上就是调用了 wsgi.Server的 start、wait方法

wsgi.Server的start()方法，启动了一个服务线程来监听请求
self._server = eventlet.spawn(eventlet.wsgi.server,

self._socket,

self.app,

protocol=self._protocol,

custom_pool=self._pool,

log=self._wsgi_logger)

经过上面的分析，可以看到，是循环的将默认的'ec2', 'osapi_compute', 'osapi_volume', 'metadata' API服务全都起来了，让它们处于监听服务状态。

这些服务的入口可以通过查看/etc/nova/api-paste.ini文件中的[app:xxxxx]部分看到，例如：

[app:osapi_compute_app_v2]

paste.app_factory = nova.api.openstack.compute:APIRouter.factory

[pipeline:oscomputeversions]

pipeline = faultwrap oscomputeversionapp

[app:osapi_volume_app_v1]

paste.app_factory = nova.api.openstack.volume:APIRouter.factory

[app:oscomputeversionapp]

paste.app_factory = nova.api.openstack.compute.versions:Versions.factory

[pipeline:osvolumeversions]

pipeline = faultwrap osvolumeversionapp

[app:osvolumeversionapp]

paste.app_factory = nova.api.openstack.volume.versions:Versions.factory

可以看到osapi_compute、osapi_volume都是启动一个“方法功能路由器”来对服务请求进行调用路由