Ocata Neutron代码分析（一）——Neutron API启动过程分析

[entry_points]
console_scripts =
    neutron-db-manage = neutron.db.migration.cli:main
    neutron-debug = neutron.debug.shell:main
    neutron-dhcp-agent = neutron.cmd.eventlet.agents.dhcp:main
    neutron-keepalived-state-change = neutron.cmd.keepalived_state_change:main
    neutron-ipset-cleanup = neutron.cmd.ipset_cleanup:main
    neutron-l3-agent = neutron.cmd.eventlet.agents.l3:main
    neutron-linuxbridge-agent = neutron.cmd.eventlet.plugins.linuxbridge_neutron_agent:main
    neutron-linuxbridge-cleanup = neutron.cmd.linuxbridge_cleanup:main
    neutron-macvtap-agent = neutron.cmd.eventlet.plugins.macvtap_neutron_agent:main
    neutron-metadata-agent = neutron.cmd.eventlet.agents.metadata:main
    neutron-netns-cleanup = neutron.cmd.netns_cleanup:main
    neutron-ns-metadata-proxy = neutron.cmd.eventlet.agents.metadata_proxy:main
    neutron-openvswitch-agent = neutron.cmd.eventlet.plugins.ovs_neutron_agent:main
    neutron-ovs-cleanup = neutron.cmd.ovs_cleanup:main
    neutron-pd-notify = neutron.cmd.pd_notify:main
    neutron-server = neutron.cmd.eventlet.server:main
    neutron-rpc-server = neutron.cmd.eventlet.server:main_rpc_eventlet
    neutron-rootwrap = oslo_rootwrap.cmd:main
    neutron-rootwrap-daemon = oslo_rootwrap.cmd:daemon
    neutron-usage-audit = neutron.cmd.eventlet.usage_audit:main
    neutron-metering-agent = neutron.cmd.eventlet.services.metering_agent:main
    neutron-sriov-nic-agent = neutron.cmd.eventlet.plugins.sriov_nic_neutron_agent:main
    neutron-sanity-check = neutron.cmd.sanity_check:main

def main():
    server.boot_server(_main_neutron_server)

def boot_server(server_func):
    # the configuration will be read into the cfg.CONF global data structure
    config.init(sys.argv[1:])
    config.setup_logging()
    config.set_config_defaults()
    if not cfg.CONF.config_file:
        sys.exit(_("ERROR: Unable to find configuration file via the default"
                   " search paths (~/.neutron/, ~/, /etc/neutron/, /etc/) and"
                   " the ‘--config-file‘ option!"))
    try:
        server_func()
    except KeyboardInterrupt:
        pass
    except RuntimeError as e:
        sys.exit(_("ERROR: %s") % e)

def _main_neutron_server():
    if cfg.CONF.web_framework == ‘legacy‘:
        wsgi_eventlet.eventlet_wsgi_server()
    else:
        wsgi_pecan.pecan_wsgi_server()

def eventlet_wsgi_server():
    neutron_api = service.serve_wsgi(service.NeutronApiService)     # 初始化neutron_api
    start_api_and_rpc_workers(neutron_api)                          # 启动neutron_api和rpc

class WsgiService(object):
    """Base class for WSGI based services.

    For each api you define, you must also define these flags:
    :_listen: The address on which to listen
    :_listen_port: The port on which to listen

    """

    def __init__(self, app_name):                    # 初始化类变量，wsgi_app变量在start函数中初始化
        self.app_name = app_name
        self.wsgi_app = None

    def start(self):
        self.wsgi_app = _run_wsgi(self.app_name)

    def wait(self):
        self.wsgi_app.wait()

class NeutronApiService(WsgiService):
    """Class for neutron-api service."""
    def __init__(self, app_name):
        profiler.setup(‘neutron-server‘, cfg.CONF.host)
        super(NeutronApiService, self).__init__(app_name)     # super调用父类的构造函数

    @classmethod
    def create(cls, app_name=‘neutron‘):
        # Setup logging early
        config.setup_logging()
        service = cls(app_name)          # 调用构造函数，app_name为neutron
        return service                   # 返回一个NeutronApiService的实例

def serve_wsgi(cls):                    # 传入的cls参数为service.NeutronApiService

    try:
        service = cls.create()          # 调用NeutronApiService.create
        service.start()                 # 初始化service.wsgi_app
    except Exception:
        with excutils.save_and_reraise_exception():
            LOG.exception(_LE(‘Unrecoverable error: please check log ‘
                              ‘for details.‘))

    registry.notify(resources.PROCESS, events.BEFORE_SPAWN, service)
    return service

def _run_wsgi(app_name):
    app = config.load_paste_app(app_name)          # 加载wsgi_app
    if not app:
        LOG.error(_LE(‘No known API applications configured.‘))
        return
    return run_wsgi_app(app)                       # 启动wsgi_server

def load_paste_app(app_name):
    """Builds and returns a WSGI app from a paste config file.

    :param app_name: Name of the application to load
    """
    loader = wsgi.Loader(cfg.CONF)
    app = loader.load_app(app_name)
    return app

class Loader(object):
    """Used to load WSGI applications from paste configurations."""

    def __init__(self, conf):
        """Initialize the loader, and attempt to find the config.

        :param conf: Application config
        :returns: None

        """
        conf.register_opts(_options.wsgi_opts)
        self.config_path = None

        config_path = conf.api_paste_config                    # 获取配置文件中api_paste_config指定的api-paste.ini文件路径
        if not os.path.isabs(config_path):
            self.config_path = conf.find_file(config_path)
        elif os.path.exists(config_path):
            self.config_path = config_path                     # 赋值给loader.config_path，供load_app中调用

        if not self.config_path:
            raise ConfigNotFound(path=config_path)

    def load_app(self, name):
        """Return the paste URLMap wrapped WSGI application.

        :param name: Name of the application to load.
        :returns: Paste URLMap object wrapping the requested application.
        :raises: PasteAppNotFound

        """
        try:
            LOG.debug("Loading app %(name)s from %(path)s",
                      {‘name‘: name, ‘path‘: self.config_path})
            return deploy.loadapp("config:%s" % self.config_path, name=name)    # 调用第三方库paste.deploy的loadapp函数来加载wsgi_app并返回，后续章节分析其配置文件  
        except LookupError:
            LOG.exception("Couldn‘t lookup app: %s", name)
            raise PasteAppNotFound(name=name, path=self.config_path)

def run_wsgi_app(app):
    server = wsgi.Server("Neutron")
    server.start(app, cfg.CONF.bind_port, cfg.CONF.bind_host,
                 workers=_get_api_workers())
    LOG.info(_LI("Neutron service started, listening on %(host)s:%(port)s"),
             {‘host‘: cfg.CONF.bind_host, ‘port‘: cfg.CONF.bind_port})
    return server

def _get_api_workers():
    workers = cfg.CONF.api_workers
    if workers is None:
        workers = processutils.get_worker_count()
    return workers

class Server(object):
    def start(self, application, port, host=‘0.0.0.0‘, workers=0):
        """Run a WSGI server with the given application."""
        self._host = host
        self._port = port
        backlog = CONF.backlog

        self._socket = self._get_socket(self._host,
                                        self._port,
                                        backlog=backlog)

        self._launch(application, workers)

    def _launch(self, application, workers=0):
        service = WorkerService(self, application, self.disable_ssl, workers)
        if workers :
            # The API service should run in the current process.
            self._server = service
            # Dump the initial option values
            cfg.CONF.log_opt_values(LOG, logging.DEBUG)
            service.start()
            systemd.notify_once()
        else:
            # dispose the whole pool before os.fork, otherwise there will
            # be shared DB connections in child processes which may cause
            # DB errors.
            api.context_manager.dispose_pool()
            # The API service runs in a number of child processes.
            # Minimize the cost of checking for child exit by extending the
            # wait interval past the default of 0.01s.
            self._server = common_service.ProcessLauncher(cfg.CONF,
                                                          wait_interval=1.0)
            self._server.launch_service(service,
                                        workers=service.worker_process_count)

class ProcessLauncher(object):
    def launch_service(self, service, workers=1):
        """Launch a service with a given number of workers.

       :param service: a service to launch, must be an instance of
              :class:`oslo_service.service.ServiceBase`
       :param workers: a number of processes in which a service
              will be running
        """
        _check_service_base(service)                        # 检查传入参数service的基类是否为oslo_service.service.ServiceBase
        wrap = ServiceWrapper(service, workers)             # 将servcie相关参数记录到wrap变量中，包括service和workers

        LOG.info(‘Starting %d workers‘, wrap.workers)
        while self.running and len(wrap.children) # 依次启动子进程，数量为wrap.workers
            self._start_child(wrap)

class WorkerService(neutron_worker.NeutronWorker):
    """Wraps a worker to be handled by ProcessLauncher"""
    def __init__(self, service, application, disable_ssl=False,
                 worker_process_count=0):
        super(WorkerService, self).__init__(worker_process_count)

        self._service = service               # service为neutron.wsgi.py中Server的实例server（run_wsgi_app函数中的server）
        self._application = application       # wsgi_app
        self._disable_ssl = disable_ssl
        self._server = None

    def start(self):
        super(WorkerService, self).start()
        # When api worker is stopped it kills the eventlet wsgi server which
        # internally closes the wsgi server socket object. This server socket
        # object becomes not usable which leads to "Bad file descriptor"
        # errors on service restart.
        # Duplicate a socket object to keep a file descriptor usable.
        dup_sock = self._service._socket.dup()
        if CONF.use_ssl and not self._disable_ssl:
            dup_sock = sslutils.wrap(CONF, dup_sock)
        self._server = self._service.pool.spawn(self._service._run,     
                                                self._application,
                                                dup_sock)          # 这里调用self._service也就是上面提到的server对象的pool（eventlet的GreenPool）
                                                                   # 的spawn函数来运行Server的_run函数

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,
                        socket_timeout=self.client_socket_timeout)

 

Neutron API部分启动过程总结：

Neutron API的启动过程是Neutron Server启动过程中的一大重要步骤，另一个为RPC部分。主要分为两个部分：wsgi app的加载和wsgi server的启动。其中，wsgi app的加载最终是调用paste.deploy库中的loadapp函数来实现的，默认的配置文件api-paste.ini在/etc/neutron目录下。wsgi server是通过进程+Eventlet的GreenPool的方式来启动服务，后面要分析的RPC服务也是通过这种方式启动。最终实例化oslo_service.service::ProcessLaucher类并调用其launch_service函数来实现，传入的service参数（这里是WorkerService ）必须是oslo_service.service::ServiceBase的派生类并需要实现start函数。