`unit-python3.11`:`ModuleNotFoundError: No module named '_contextvars'` with non-root user and `uv`

[alexei]

Bug Overview

I have a Python project that uses uv. When I install uv and set up the virtual environment using a non-root user, nginx-unit won't apply the configuration:

curl -X PUT --data-binary @/path/to/project/config.json  --unix-socket /var/run/control.unit.sock http://localhost/config/
{
	"error": "Failed to apply new configuration."
}

The log reveals:

Traceback (most recent call last):
  File "/path/to/app/src/app/project/wsgi.py", line 3, in <module>
    from django.core.wsgi import get_wsgi_application
  File "/path/to/app/.venv/lib/python3.11/site-packages/django/core/wsgi.py", line 2, in <module>
    from django.core.handlers.wsgi import WSGIHandler
  File "/path/to/app/.venv/lib/python3.11/site-packages/django/core/handlers/wsgi.py", line 3, in <module>
    from django.conf import settings
  File "/path/to/app/.venv/lib/python3.11/site-packages/django/conf/__init__.py", line 19, in <module>
    from django.utils.deprecation import RemovedInDjango60Warning
  File "/path/to/app/.venv/lib/python3.11/site-packages/django/utils/deprecation.py", line 4, in <module>
    from asgiref.sync import iscoroutinefunction, markcoroutinefunction, sync_to_async
  File "/path/to/app/.venv/lib/python3.11/site-packages/asgiref/sync.py", line 1, in <module>
    import asyncio
  File "/home/myuser/.local/share/uv/python/cpython-3.11.12-linux-x86_64-gnu/lib/python3.11/asyncio/__init__.py", line 8, in <module>
    from .base_events import *
  File "/home/myuser/.local/share/uv/python/cpython-3.11.12-linux-x86_64-gnu/lib/python3.11/asyncio/base_events.py", line 41, in <module>
    from . import events
  File "/home/myuser/.local/share/uv/python/cpython-3.11.12-linux-x86_64-gnu/lib/python3.11/asyncio/events.py", line 18, in <module>
    import contextvars
  File "/home/myuser/.local/share/uv/python/cpython-3.11.12-linux-x86_64-gnu/lib/python3.11/contextvars.py", line 1, in <module>
    from _contextvars import Context, ContextVar, Token, copy_context
ModuleNotFoundError: No module named '_contextvars'

I think it's important to note I was able to have it up and running a couple of times:

1. The first time I accidentally ran everything as root (installed uv, set up the venv etc.) then chown-ed the app directory to unit, and that worked.
2. The second time, I gave up on uv and used the system Python to set up the env as myuser etc. and that worked.

Now I'm back to trying to set everything up as myuser. I re-ran just to be sure:

chown -R myuser:mygroup /path/to/app/
chmod -R u+rwx /path/to/app/

Given _contextvars is definitely not missing from either system-Python or uv-Python, and that it worked when I set everything up as root, I'm now inclined to think it's a permissions issue. The error message and traceback are not giving away that much, though.

There's an older discussion that appears to be similar - https://github.com/nginx/unit/issues/516 - and if I understand it correctly, the issue there is the unit user doesn't have sufficient access to the venv. I added unit to the group (usermod -a -G unit mygroup) and changed permissions (chmod -R g+rwx /path/to/app/):

$ ls -la /path/to/app/.venv/
total 32
drwxrwxr-x 5 myuser mygroup 4096 Jun  3 09:20 .
drwxrwxr-x 5 myuser mygroup 4096 Jun  3 09:19 ..
-rwxrwxr-- 1 myuser mygroup    1 Jun  3 09:19 .gitignore
-rwxrwxr-- 1 myuser mygroup   43 Jun  3 09:19 CACHEDIR.TAG
drwxrwxr-x 2 myuser mygroup 4096 Jun  3 09:20 bin
drwxrwxr-x 3 myuser mygroup 4096 Jun  3 09:20 include
drwxrwxr-x 3 myuser mygroup 4096 Jun  3 09:19 lib
lrwxrwxrwx 1 myuser mygroup    3 Jun  3 09:19 lib64 -> lib
-rwxrwxr-- 1 myuser mygroup  191 Jun  3 09:19 pyvenv.cfg

That didn't do the trick.

Expected Behavior

I'm expecting it to work.

Steps to Reproduce the Bug

uv python install 3.11.12
uv venv --python 3.11.12

etc.

Environment Details

• Target deployment platform: VPS
• Target OS: Debian 12
• Version of this project or specific commit: unit 1.34.2
• Version of any relevant project languages: Python (system) 3.11.2, uv 0.7.9, uv Python (uv) 3.11.12

Additional Context

Fwiw, config.json looks like:

{
  "listeners": {
    "*:9001": {
      "pass": "routes"
    }
  },
  "routes": [
    {
      "action": {
        "pass": "applications/app"
      }
    }
  ],
  "applications": {
    "app": {
      "type": "python",
      "user": "myuser",
      "group": "mygroup",
      "path": "/path/to/app/",
      "home": "/path/to/app/.venv/",
      "module": "app.project.wsgi",
      "callable": "application",
      "environment": {
        etc.
      }
    }
  }
}

[Pavel-Hadzhiyski]

Exact same issue here.

EDIT: I figured out what the problem was. Turns out it's not a compatibility or permission issue when using uv and unit - it's a conflict between the unit-python version and the python version used when creating your virtual environment. In my case I had a python3.12 venv, but was loading unit-python3.10 in my Dockerfile. I simply went in my pyproject.toml and changed my python version 3.10: requires-python = "==3.10.*" Now when I rebuild my docker container - my venv is using the same version as unit-python and my unit configuration loaded just fine. Hope this helps OP too.

[alexei]

@Pavel-Hadzhiyski thanks for your input, and I apologise for the late reply -- I believe I missed your edit. I need to ask: were you building the venv with system Python, or uv Python?