记一次 gunicorn 启动 flask 出问题的经历

出错现象:

gunicorn+nginx+flask 部署项目, 部署过程没问题,项目也正常启动了,但是一旦访问接口,就会报错:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/gunicorn/workers/sync.py", line 135, in handle
    self.handle_request(listener, req, client, addr)
  File "/usr/local/lib/python3.6/dist-packages/gunicorn/workers/sync.py", line 176, in handle_request
    respiter = self.wsgi(environ, resp.start_response)
TypeError: __call__() takes from 1 to 2 positional arguments but 3 were given

但是我通过 runserver运行的话,是没有问题的,外网可以正常访问.

所以问题就出在gunicorn 和 flask 的 wsgi 对接上.

gunicorn 启动时的方式是 gunicorn [options] file:app

我其他方面想了很多,试了很多,都没解决, 然后盯着这句话想了一二十分钟........ 嗯.......可能是这个原因:

直接通过终端 runserver方式启动的话,会直接运行启动文件, 最终提供服务的是app (就是flask的实例)

我为了数据库迁移, 启动文件注册了flask-script的对象,最后启动的实际是flask-script对象, 这个对象提供的就是些命令行之类的东西, 简单地说,就是一个命令行扩展, 在不使用命令行迁移数据库的时候没什么用(至少我小白看来是这样).

这就出来个想法了.

gunicorn说白了就是服务代理, 用来处理高并发的, 通过多进程/协程/线程的方式提供并发访问, 所以gunicorn 代理的是flask对象, 也就是flask实例化的APP.

我的启动文件代码大概如下:

from projects import APP, db
from flask_migrate import Migrate, MigrateCommand
from flask_script import Manager

manage = Manager(APP)
migrate = Migrate(app=APP, db=db)
manage.add_command('db', MigrateCommand)

if __name__ == '__main__':
    manage.run()

我这次的错误就在于将 flask-script的实例提供给了gunicorn, 这就导致了gunicorn接收到的参数并不是标准wsgi参数,所以报错.

解决办法很简单: 将APP(对于此处而言)交给gunicorn代理就好了.

所以gunicorn的启动命令改成:

1 gunicorn -D -w 3 -t 300 -b 0.0.0.0:5000 manage:APP

有需要的话,加上日志的配置,个人建议最好加上日志,日志是处理问题的最直接资料

gunicorn -D --error-logfile=/logs/gunicorn.log --pid=/logs/gunicorn.pid --access-logfile=/logs/access.log -w 3 -t 300 -b 0.0.0.0:5000 manage:APP

所以本次问题的原因在于wsgi协议未被标准的执行,代理服务器代理的是服务器APP, 而我一直没注意到这个.

下面是flask-script在终端直接runserver时的运行机制:

如我上方代码所示,manage是flask-script的实例, 执行Python manage时, 会执行该实例的run()方法

def run(self, commands=None, default_command=None):
        """
        Prepares manager to receive command line input. Usually run
        inside "if __name__ == "__main__" block in a Python script.

        :param commands: optional dict of commands. Appended to any commands
                         added using add_command().

        :param default_command: name of default command to run if no
                                arguments passed.
        """

        if commands:
            self._commands.update(commands)

        # Make sure all of this is Unicode
        argv = list(text_type(arg) for arg in sys.argv)
        if default_command is not None and len(argv) == 1:
            argv.append(default_command)

        try:
            result = self.handle(argv[0], argv[1:])
        except SystemExit as e:
            result = e.code

        sys.exit(result or 0)

如上方法会执行 handle() 然后通过一系列的方法,路过执行如下代码:

def add_default_commands(self):
        """
        Adds the shell and runserver default commands. To override these,
        simply add your own equivalents using add_command or decorators.
        """

        if "shell" not in self._commands:
            self.add_command("shell", Shell())
        if "runserver" not in self._commands:
            self.add_command("runserver", Server())

上面的代码会给flask-script对象添加两个命令,其中就有我们很熟悉的 runserver, 该命令会执行Server()对象的call方法,call方法如下:

def __call__(self, app, host, port, use_debugger, use_reloader,
                 threaded, processes, passthrough_errors, ssl_crt, ssl_key):
        # we don't need to run the server in request context
        # so just run it directly

        if use_debugger is None:
            use_debugger = app.debug
            if use_debugger is None:
                use_debugger = True
                if sys.stderr.isatty():
                    print("Debugging is on. DANGER: Do not allow random users to connect to this server.", file=sys.stderr)
        if use_reloader is None:
            use_reloader = use_debugger

        if None in [ssl_crt, ssl_key]:
            ssl_context = None
        else:
            ssl_context = (ssl_crt, ssl_key)

        app.run(host=host,
                port=port,
                debug=use_debugger,
                use_debugger=use_debugger,
                use_reloader=use_reloader,
                threaded=threaded,
                processes=processes,
                passthrough_errors=passthrough_errors,
                ssl_context=ssl_context,
                **self.server_options)