Werkzeug 2.1.0 fails with WERKZEUG_SERVER_FD error

[sfuerte]

Upgrading to 2.1.0 leads to the following error:

"message": "Starting REST API"
"message": "'WERKZEUG_SERVER_FD'", 
"exc_info": "Traceback (most recent call last):
  ...
  self.app.run(host=self.host, port=self.port, debug=self.debug)
  File \"/usr/local/lib/python3.9/dist-packages/connexion/apps/flask_app.py\", line 104, in run
  self.app.run(self.host, port=self.port, debug=self.debug, **options)
  File \"/usr/local/lib/python3.9/dist-packages/flask/app.py\", line 920, in run
  run_simple(t.cast(str, host), port, self, **options)
  File \"/usr/local/lib/python3.9/dist-packages/werkzeug/serving.py\", line 1047, in run_simple
  fd = int(os.environ[\"WERKZEUG_SERVER_FD\"])
  File \"/usr/lib/python3.9/os.py\", line 679, in __getitem__
  raise KeyError(key) from None
  KeyError: 'WERKZEUG_SERVER_FD'"
"message": "SHUTDOWN"

Environment:

$ lsb_release -d
Description:	Debian GNU/Linux 11 (bullseye)

$ python3 --version
Python 3.9.2

# selected packages
$ pip3 list
Package               Version
--------------------- --------------
connexion             2.13.0
Flask                 2.1.0
Werkzeug              2.1.0

Workaround:

freezing Werkzeug @ 2.0.3 in requirements.txt (which we didn't have before as don't use it directly but it's rather a prerequisite of connexion and Flask)

Werkzeug==2.0.3

[davidism]

Looks like something you're using is messing with the dev server internals in a way that tricks it into thinking it's running in the reloader when it's not. Since it's not actually running in the reloader, certain things that it expects aren't set up correctly. You'll need to identify and report this to whatever is running the server this way.

[RobbeSneyders]

@davidism could you point me to where connexion is messing with the dev server internals? I'm having a hard time reproducing the issue.

[davidism]

Yeah, I had a look and can't reproduce this either. If anyone is setting WERKZEUG_RUN_MAIN manually for some reason, that's what would mess with it. I updated the original comment.

[sfuerte]

@davidism, thanks for the hint. Apparently, it was set in systemd service file, removing that solved the issue.

# required to disable Flask debugging banner: "Serving Flask app (lazy loading) ..."
Environment="WERKZEUG_RUN_MAIN=true"

[davidism]

The fact that you're running this in systemd indicates a severe security issue with that application. Do not run the development server in production. It is not intended to be secure, stable, or efficient. Use a production server such as gunicorn, uwsgi, waitress, or mod_wsgi. The fact that you have to set an internal variable just to disable this message should be a strong indicator that you're doing something incorrect.

[sfuerte]

Thanks for the info. Will review what was done there :)