nova-api源码-启动服务

结构地图

nova-api服务是nova组件的入口，在启动时存在大量初始化的操作，比如加载api、创建wsgi server、策略加载等。对于openstack中所有组件而言，项目中的setup.cfg文件，就是组件的结构地图，其中包含了所有服务的入口。

console_scripts =
    nova-api = nova.cmd.api:main
    nova-api-metadata = nova.cmd.api_metadata:main
    nova-api-os-compute = nova.cmd.api_os_compute:main
    nova-compute = nova.cmd.compute:main
    nova-conductor = nova.cmd.conductor:main
    nova-manage = nova.cmd.manage:main
    nova-novncproxy = nova.cmd.novncproxy:main
    nova-policy = nova.cmd.policy:main
    nova-rootwrap = oslo_rootwrap.cmd:main
    nova-rootwrap-daemon = oslo_rootwrap.cmd:daemon
    nova-scheduler = nova.cmd.scheduler:main
    nova-serialproxy = nova.cmd.serialproxy:main
    nova-spicehtml5proxy = nova.cmd.spicehtml5proxy:main
    nova-status = nova.cmd.status:main

线上环境也可以通过查看entry_points文件：

# /usr/lib/python2.7/site-packages/nova-20.6.0-py2.7.egg-info/entry_points.txt
[console_scripts]
nova-api = nova.cmd.api:main
nova-api-metadata = nova.cmd.api_metadata:main
nova-api-os-compute = nova.cmd.api_os_compute:main
nova-compute = nova.cmd.compute:main
nova-conductor = nova.cmd.conductor:main
nova-console = nova.cmd.console:main
nova-dhcpbridge = nova.cmd.dhcpbridge:main
nova-manage = nova.cmd.manage:main
nova-network = nova.cmd.network:main
nova-novncproxy = nova.cmd.novncproxy:main
nova-policy = nova.cmd.policy:main
nova-rootwrap = oslo_rootwrap.cmd:main
nova-rootwrap-daemon = oslo_rootwrap.cmd:daemon
nova-scheduler = nova.cmd.scheduler:main
nova-serialproxy = nova.cmd.serialproxy:main
nova-spicehtml5proxy = nova.cmd.spicehtml5proxy:main
nova-status = nova.cmd.status:main
nova-xvpvncproxy = nova.cmd.xvpvncproxy:main

服务入口

nova-api的入口文件：

# nova/cmd/api.py
def main():
    config.parse_args(sys.argv)
    logging.setup(CONF, "nova")
    objects.register_all()
    gmr_opts.set_defaults(CONF)
    if 'osapi_compute' in CONF.enabled_apis:
        # NOTE(mriedem): This is needed for caching the nova-compute service
        # version.
        objects.Service.enable_min_version_cache()
    log = logging.getLogger(__name__)

    gmr.TextGuruMeditation.setup_autorun(version, conf=CONF)

    launcher = service.process_launcher()
    started = 0
    for api in CONF.enabled_apis:
        should_use_ssl = api in CONF.enabled_ssl_apis
        try:
            server = service.WSGIService(api, use_ssl=should_use_ssl)
            launcher.launch_service(server, workers=server.workers or 1)
            started += 1
        except exception.PasteAppNotFound as ex:
            log.warning("%s. ``enabled_apis`` includes bad values. "
                        "Fix to remove this warning.", ex)

    if started == 0:
        log.error('No APIs were started. '
                  'Check the enabled_apis config option.')
        sys.exit(1)

    launcher.wait()

服务启动时，config.parse_args(sys.argv)就先获取配置参数。nova服务的配置在/etc/nova/nova.conf文件中。

[DEFAULT]

#
# From nova.conf
#

#
# Availability zone for internal services. For more information, refer to the
# documentation. (string value)
#internal_service_availability_zone=internal

#
# Default availability zone for compute services. For more information, refer to
# the documentation. (string value)
#default_availability_zone=nova
... ...

nova-api入口函数中最重要的两句代码为：

server = service.WSGIService(api, use_ssl=should_use_ssl)
launcher.launch_service(server, workers=server.workers or 1)

根据nova参数配置中的enabled_apis选项，先声明一个WSGIService实例，第一个参数就是enabled_apis中配置的一项，再通过launch_service启动这个WSGI服务。

配置加载

# nova/config.py
def parse_args(argv, default_config_files=None, configure_db=True,
               init_rpc=True):
    log.register_options(CONF)

    # NOTE(sean-k-mooney): this filter addresses bug #1825584
    # https://bugs.launchpad.net/nova/+bug/1825584
    # eventlet monkey-patching breaks AMQP heartbeat on uWSGI
    rabbit_logger = logging.getLogger('oslo.messaging._drivers.impl_rabbit')
    rabbit_logger.addFilter(rabbit_heartbeat_filter)
	# 配置默认值  包括wsgi服务中间件   消息队列交换器
    set_lib_defaults()
    if profiler:
        profiler.set_defaults(CONF)

    CONF(argv[1:],
         project='nova',
         version=version.version_string(),
         default_config_files=default_config_files)
	# 声明一个rpc server
    if init_rpc:
        rpc.init(CONF)

    if configure_db:
        main_db_api.configure(CONF)
        api_db_api.configure(CONF)

配置默认值：

def set_lib_defaults():
    """Update default value for configuration options from other namespace.

    Example, oslo lib config options. This is needed for
    config generator tool to pick these default value changes.
    https://docs.openstack.org/oslo.config/latest/cli/
    generator.html#modifying-defaults-from-other-namespaces
    """

    # Update default value of oslo.middleware cors config option.
    middleware.set_defaults()

    # Update default value of RPC transport control_exchange config option.
    rpc.set_defaults(control_exchange='nova')

    # Update default value of oslo_log default_log_levels and
    # logging_context_format_string config option.
    set_log_defaults()

    # Update default value of oslo.policy policy_file config option.
    policy_opts.set_defaults(CONF, policy.DEFAULT_POLICY_FILE)

WSGI启动

# 声明一个process_launcher实例
launcher = service.process_launcher()
# 声明WSGI
server = service.WSGIService(api, use_ssl=should_use_ssl)
# 加入launcher中启动
launcher.launch_service(server, workers=server.workers or 1)

launcher声明实际调用oslo-service库实现

# nova/service.py
def process_launcher():
    return service.ProcessLauncher(CONF, restart_method='mutate')

oslo-service：

# oslo_service/service.py 
class ProcessLauncher(object):
    """Launch a service with a given number of workers."""

    def __init__(self, conf, wait_interval=0.01, restart_method='reload'):
        """Constructor.

        :param conf: an instance of ConfigOpts
        :param wait_interval: The interval to sleep for between checks
                              of child process exit.
        :param restart_method: If 'reload', calls reload_config_files on
            SIGHUP. If 'mutate', calls mutate_config_files on SIGHUP. Other
            values produce a ValueError.
        """
        self.conf = conf
        conf.register_opts(_options.service_opts)
        self.children = {}
        self.sigcaught = None
        self.running = True
        self.wait_interval = wait_interval
        self.launcher = None
        rfd, self.writepipe = os.pipe()
        self.readpipe = eventlet.greenio.GreenPipe(rfd, 'r')
        self.signal_handler = SignalHandler()
        self.handle_signal()
        self.restart_method = restart_method
        if restart_method not in _LAUNCHER_RESTART_METHODS:
            raise ValueError(_("Invalid restart_method: %s") % restart_method)

WSGI实例：

# nova/service.py
class WSGIService(service.Service):
    """Provides ability to launch API from a 'paste' configuration."""

    def __init__(self, name, loader=None, use_ssl=False, max_url_len=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
        # NOTE(danms): Name can be metadata, osapi_compute, per
        # nova.service's enabled_apis
        self.binary = 'nova-%s' % name

        LOG.warning('Running %s using eventlet is deprecated. Deploy with '
                    'a WSGI server such as uwsgi or mod_wsgi.', self.binary)

        self.topic = None
        self.manager = self._get_manager()
        self.loader = loader or api_wsgi.Loader()
        self.app = self.loader.load_app(name)
        # inherit all compute_api worker counts from osapi_compute
        if name.startswith('openstack_compute_api'):
            wname = 'osapi_compute'
        else:
            wname = name
        self.host = getattr(CONF, '%s_listen' % name, "0.0.0.0")
        self.port = getattr(CONF, '%s_listen_port' % name, 0)
        self.workers = (getattr(CONF, '%s_workers' % wname, None) or
                        processutils.get_worker_count())
        if self.workers and self.workers < 1:
            worker_name = '%s_workers' % name
            msg = (_("%(worker_name)s value of %(workers)s is invalid, "
                     "must be greater than 0") %
                   {'worker_name': worker_name,
                    'workers': str(self.workers)})
            raise exception.InvalidInput(msg)
        self.use_ssl = use_ssl
        self.server = wsgi.Server(name,
                                  self.app,
                                  host=self.host,
                                  port=self.port,
                                  use_ssl=self.use_ssl,
                                  max_url_len=max_url_len)
        # Pull back actual port used
        self.port = self.server.port
        self.backdoor_port = None
        setup_profiler(name, self.host)

启动WSGI

    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)
        wrap = ServiceWrapper(service, workers)

        # Hide existing objects from the garbage collector, so that most
        # existing pages will remain in shared memory rather than being
        # duplicated between subprocesses in the GC mark-and-sweep. (Requires
        # Python 3.7 or later.)
        if hasattr(gc, 'freeze'):
            gc.freeze()

        LOG.info('Starting %d workers', wrap.workers)
        while self.running and len(wrap.children) < wrap.workers:
            self._start_child(wrap)
            
    def _start_child(self, wrap):
        if len(wrap.forktimes) > wrap.workers:
            # Limit ourselves to one process a second (over the period of
            # number of workers * 1 second). This will allow workers to
            # start up quickly but ensure we don't fork off children that
            # die instantly too quickly.
            if time.time() - wrap.forktimes[0] < wrap.workers:
                LOG.info('Forking too fast, sleeping')
                time.sleep(1)

            wrap.forktimes.pop(0)

        wrap.forktimes.append(time.time())

        pid = os.fork()
        if pid == 0:
            self.launcher = self._child_process(wrap.service)
            while True:
                self._child_process_handle_signal()
                status, signo = self._child_wait_for_exit_or_signal(
                    self.launcher)
                if not _is_sighup_and_daemon(signo):
                    self.launcher.wait()
                    break
                self.launcher.restart()

            os._exit(status)

        LOG.debug('Started child %d', pid)

        wrap.children.add(pid)
        self.children[pid] = wrap

        return pid