Glance组件之深入探索『3』——源码框架分析

# filename: glance/cmd/api.py
def main():
    try:
        # config.parse_args()中会确认要加载的配置文件的绝对路径
        # 并且将配置文件中的配置存放到config.CONF中供后续调用
        config.parse_args()    
        # 设置eventlet的hub，配置文件中没有该配置选项，代码中默认值为poll
        wsgi.set_eventlet_hub()
        log.setup('glance')

        # 初始化后端存储，注册与后端存储（filesystem、eqlx、ceph等）相关的控制模块，
        # 并校验默认存储方式。
        glance_store.register_opts(config.CONF)
        glance_store.create_stores(config.CONF)    
        glance_store.verify_default_store()

        # 确认是否启用OpenStack分析功能
        if cfg.CONF.profiler.enabled:
            _notifier = osprofiler.notifier.create("Messaging",
                                                   notifier.messaging, {},
                                                   notifier.get_transport(),
                                                   "glance", "api",
                                                   cfg.CONF.bind_host)
            osprofiler.notifier.set(_notifier)
        else:
            osprofiler.web.disable()

        # 通过wsgi.Server()创建一个http服务器（使用了eventlet绿色线程(协程)），
        # 调用start()方法启动服务器。
        # server.wait()让server等待接收http rest查询。
        server = wsgi.Server()
        server.start(config.load_paste_app('glance-api'), default_port=9292)
        server.wait()

# filename glance/common/config.py 
def load_paste_app(app_name, flavor=None, conf_file=None): 
    # 根据配置文件(glance-api.conf)的配置，确定最终的app_name，
    # 例如配置文件中flavor=keystone，则app_name=glance-api-keystone
    app_name += _get_deployment_flavor(flavor)    

    if not conf_file:
        # 获取paste的配置文件的绝对路径
        conf_file = _get_deployment_config_file()    

    try:
        logger = logging.getLogger(__name__)
        logger.debug("Loading %(app_name)s from %(conf_file)s",
                     {'conf_file': conf_file, 'app_name': app_name})

        # 调用paste.deploy中的loadapp()函数加载paste配置文件中的app_name对应的app
        # (例如glance-api-keystone)
        app = deploy.loadapp("config:%s" % conf_file, name=app_name)    

        return app

def _get_deployment_flavor(flavor=None):
    if not flavor:
        # 读取配置文件(glance-api.conf)中[paste_deploy]配置块中flavor参数的配置。
        # from oslo.config import cfg  ==>  CONF = cfg.CONF
        # 这就属于oslo.config项目的内容了，有时间单开一篇介绍细节部分
        flavor = CONF.paste_deploy.flavor    
    # 如果配置文件中配置了flavor，则返回'-参数内容'，
    # 例如配置文件中flavor=keystone，则返回'-keystone'
    return '' if not flavor else ('-' + flavor)   

def _get_deployment_config_file():
    # 读取配置文件(glance-api.conf)中[paste_deploy]配置块中config_file参数的配置。
    path = CONF.paste_deploy.config_file    
    if not path:
        # 如果配置文件中未配置config_file参数，则根据program名字生成path
        path = _get_paste_config_path()    
    if not path:
        msg = _("Unable to locate paste config file for %s.") % CONF.prog
        raise RuntimeError(msg)
    return os.path.abspath(path)

# filename: glance/common/wsgi.py
def start(self, application, default_port):
    """
    Run a WSGI server with the given application.

    :param application: The application to be run in the WSGI server
    :param default_port: Port to bind to if none is specified in conf
    """
    self.application = application
    self.sock = get_socket(default_port)
    if CONF.workers == 0:
        # Useful for profiling, test, debug etc.
        self.pool = self.create_pool()
        self.pool.spawn_n(self._single_run, self.application, self.sock)
        return
    else:
        self.logger.info(_("Starting %d workers") % CONF.workers)
        signal.signal(signal.SIGTERM, kill_children)
        signal.signal(signal.SIGINT, kill_children)
        signal.signal(signal.SIGHUP, hup)
        while len(self.children) < CONF.workers:
            self.run_child()

def run_child(self):
    pid = os.fork()
    if pid == 0:
        signal.signal(signal.SIGHUP, signal.SIG_DFL)
        signal.signal(signal.SIGTERM, signal.SIG_DFL)
        # ignore the interrupt signal to avoid a race whereby
        # a child worker receives the signal before the parent
        # and is respawned unnecessarily as a result
        signal.signal(signal.SIGINT, signal.SIG_IGN)
        self.run_server()
        self.logger.info(_('Child %d exiting normally') % os.getpid())
        # self.pool.waitall() has been called by run_server, so
        # its safe to exit here
        sys.exit(0)
    else:
        self.logger.info(_('Started child %s') % pid)
        self.children.append(pid)

def run_server(self):
    """Run a WSGI server."""
    if cfg.CONF.pydev_worker_debug_host:
        utils.setup_remote_pydev_debug(cfg.CONF.pydev_worker_debug_host,
                                       cfg.CONF.pydev_worker_debug_port)

    eventlet.wsgi.HttpProtocol.default_request_version = "HTTP/1.0"
    #创建一个eventlet协程池
    self.pool = self.create_pool()
    try:
        #将application放到eventlet协程池里运行，start动作完成。
        eventlet.wsgi.server(self.sock,
                             self.application,
                             log=logging.WritableLogger(self.logger),
                             custom_pool=self.pool,
                             debug=False)
    except socket.error as err:
        if err[0] != errno.EINVAL:
            raise
    self.pool.waitall()

def create_pool(self):
    return eventlet.GreenPool(size=self.threads)

# filename: glance/common/config.py
# 从oslo.config中导入cfg
from oslo.config import cfg

# 定义名为“paste_deploy”的参数组，其中包含两个选项：flavor、config_file
# 这两个参数对应了glance-api.conf配置文件里的以下部分的配置：
# [paste_deploy]
# flavor=
# config_file =
paste_deploy_opts = [
    cfg.StrOpt('flavor',
               help=_('Partial name of a pipeline in your paste configuration '
                      'file with the service name removed. For example, if '
                      'your paste section name is '
                      '[pipeline:glance-api-keystone] use the value '
                      '"keystone"')),
    cfg.StrOpt('config_file',
               help=_('Name of the paste configuration file.')),
]
CONF = cfg.CONF
# 注册多个选项
CONF.register_opts(paste_deploy_opts, group='paste_deploy')

# glance/cmd/api.py 中的config.parse_args() 部分调用该方法找到配置文件，
# 并将配置文件的内容加载到CONF中，需要获取某个配置项时，
# 通过CONF.groupname.option调用即可，
# 可以参考_get_deployment_flavor()中的例子
def parse_args(args=None, usage=None, default_config_files=None):
    CONF(args=args,
         project='glance',
         version=version.cached_version_string(),
         usage=usage,
         default_config_files=default_config_files)

def _get_deployment_flavor(flavor=None):
    if not flavor:
        # 当需要获取配置文件中的flavor配置项时,
        # 调用CONF.paste_deploy.flavor即可
        flavor = CONF.paste_deploy.flavor
    return '' if not flavor else ('-' + flavor)

# Use this pipeline for keystone auth
[pipeline:glance-api-keystone]
pipeline = versionnegotiation osprofiler authtoken context  rootapp

[composite:rootapp]
paste.composite_factory = glance.api:root_app_factory
/: apiversions
/v1: apiv1app
/v2: apiv2app

[app:apiversions]
paste.app_factory = glance.api.versions:create_resource

[app:apiv1app]
paste.app_factory = glance.api.v1.router:API.factory

[app:apiv2app]
paste.app_factory = glance.api.v2.router:API.factory

# 检查请求中的版本信息，如果请求的不是当前所支持的版本，则返回当前支持的版本信息
[filter:versionnegotiation]
paste.filter_factory = glance.api.middleware.version_negotiation:VersionNegotiationFilter.factory

# 用来enables tracing for an application。似乎是在 enabled = yes 的情况下，记录 request 的一些信息。具体功能需要后续研究。
[filter:osprofiler]
paste.filter_factory = osprofiler.web:WsgiMiddleware.factory
hmac_keys = SECRET_KEY
enabled = yes

# 该 filter 会通过校验request所带的 token 来校验用户身份。当request来的时候，它根据 token 来判断这个请求是否合法。校验失败则直接返回 401 错误，校验通过则提取 token 中的信息，放入到env中，供后续的其它app使用。
[filter:authtoken]
paste.filter_factory = keystonemiddleware.auth_token:filter_factory
delay_auth_decision = true

# 将认证信息保存到context中，供后续app调用。
[filter:context]
paste.filter_factory = glance.api.middleware.context:ContextMiddleware.factory