Gunicorn ImportError: cannot import name 'ALREADY_HANDLED' from 'eventlet.wsgi' in docker

Question

I had a working code running flask with gunicorn (eventlet worker) in docker. It's also working in production, but on my machine, it started doing this. I can't find anything on google about this thing. What meight be the problem?

Error: class uri 'eventlet' invalid or not found:
web_1       |
web_1       | [Traceback (most recent call last):
web_1       |   File "/root/.local/lib/python3.7/site-packages/gunicorn/util.py", line 99, in load_class
web_1       |     mod = importlib.import_module('.'.join(components))
web_1       |   File "/usr/local/lib/python3.7/importlib/__init__.py", line 127, in import_module
web_1       |     return _bootstrap._gcd_import(name[level:], package, level)
web_1       |   File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
web_1       |   File "<frozen importlib._bootstrap>", line 983, in _find_and_load
web_1       |   File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
web_1       |   File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
web_1       |   File "<frozen importlib._bootstrap_external>", line 728, in exec_module
web_1       |   File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
web_1       |   File "/root/.local/lib/python3.7/site-packages/gunicorn/workers/geventlet.py", line 20, in <module>
web_1       |     from eventlet.wsgi import ALREADY_HANDLED as EVENTLET_ALREADY_HANDLED
web_1       | ImportError: cannot import name 'ALREADY_HANDLED' from 'eventlet.wsgi' (/root/.local/lib/python3.7/site-packages/eventlet/wsgi.py)
web_1       | ]

Answer 1

Looks like there was a change recently to eventlet

See this PR for an example patch, and potential release version: https://github.com/benoitc/gunicorn/pull/2581

Eventlet 0.30.3+ removed wsgi.ALREADY_HANDLED breaking public API in just a patch version increase. Sorry.

Issue with ALREADY_HANDLED: eventlet/eventlet#543 Solution with WSGI_LOCAL: eventlet/eventlet#544

It's recommended to use eventlet>=0.31.0 if one uses websockets, because older versions are vulnerable to DoS attack. GHSA-9p9m-jm8w-94p2

CI failed in pylint checks on lines I didn't touch.

Answer 2

I had exactly the same error when trying to use SocketIO with Flask and found the answer at https://localcoder.org/deploy-flask-socketio-on-beanstalk

I was able to get this running as per their suggestion:

pip uninstall gunicorn
pip uninstall eventlet
pip install gunicorn==20.1.0
pip install eventlet==0.30.2

gunicorn --worker-class eventlet -w 1 app:app

Environment: AWS ALB -> EC2/Linux2 (python 3.8.5, Flask Socket.IO)