HOWTO run Flask under uwsgi on Opalstack

ssherlock

kylotan Thanks, I will try and remember that, but since adding to PYTHONPATH all is working fine now.
Cheers

kylotan

Okay, but obviously be aware that relying on a change to PYTHONPATH will mean it only works in that particular context - whereas if you can fix it inside the package, it would work everywhere. 🙂

23f23f

I am somewhat new to flask, but I believe I am following the tutorial exactly step by step, but I keep getting the following errors in the uwsgi.log

*** Operational MODE: preforking+threaded ***
mounting myproject:app on /
Traceback (most recent call last):
File "./myproject/init.py", line 4, in <module>
from hello import app
ModuleNotFoundError: No module named 'hello'
unable to load app 0 (mountpoint='/') (callable not found or import error)
*** no app loaded. going in full dynamic mode ***

sean

23f23f check two things:

Ensure that your hello directory contains a file named __init__.py
Ensure that the parent directory that contains hello is on your Python search path, ie python-path = /home/you/apps/appname/dirname in your uwsgi.ini.

Restart your app after making any necessary changes.

23f23f

I am wondering if the following is possible:

I have installed a new version of python (3.8) using this: https://community.opalstack.com/d/204-howto-install-a-newer-or-older-version-of-python
I have set up a uwsgi app called OPALTEST (which has corresponding path /home/MYUSERNAME/apps/OPALTEST)
I have uploaded a flask app to another folder: /home/MYUSERNAME/some/other/folder/MYFLASKAPP)

I can get things to run fine with this uwsgi.ini file:

[uwsgi]
master = True
http = 127.0.0.1:31267
virtualenv = /home/MYUSERNAME/apps/OPALTEST/env/
daemonize = /home/MYUSERNAME/logs/apps/OPALTEST/uwsgi.log
pidfile = /home/MYUSERNAME/apps/OPALTEST/tmp/OPALTEST.pid
workers = 2
threads = 2

# adjust the following to point to your project
python-path = /home/MYUSERNAME/some/other/folder/MYFLASKAPP/
mount = /=myapp:app
manage-script-name = True
touch-reload = /home/MYUSERNAME/some/other/folder/MYFLASKAPP/myapp/hello.py

However, this uses python 3.6. I have a separate env in /home/MYUSERNAME/some/other/folder/MYFLASKAPP/venv/bin/activate, but I can't seem to get it working with the new python3.8 version.

sean

23f23f

Change the virtualenv in uwsgi.ini to /home/MYUSERNAME/some/other/folder/MYFLASKAPP/venv
Ensure that you've installed uwsgi into your other virtualenv (ie pip install uwsgi
Edit the app's start and stop scripts to run /home/MYUSERNAME/some/other/folder/MYFLASKAPP/venv/bin/uwsgi instead of /home/MYUSERNAME/apps/OPALTEST/env/bin/uwsgi.

Danos2000

I've had a flask app running for a couple years without issue using these instructions. I was just informed that the site it powers is down (not sure how long it's been down it's low-traffic) and when I investigate, it seems like most of the errors are maybe path-related? (ModuleNotFound errors, and the main one posted below.) Has anything changed on the servers recently that would explain this? (vps91)

--- no python application found, check your startup logs for errors ---

UPDATE
I had to newly add a sub-path to my python-path declarations in uwsgi.ini, and it's working again now.

sean

Danos2000 No, there have been no changes on your server that would cause this.

To troubleshoot, do a full stop/start cycle of the app then immediately open your uwsgi log to see what errors are logged immediately before the most recent "no python application found" error. That should give you an indication of the module that can't be found and you can then adjust your python-path in uwsgi.ini accordingly.

If you're unsure how to proceed after viewing the log then please email our support team with the details and we'll look into it further.

sean

I've edited the original post to simplify it a bit, mainly:

The __init__.py file is now blank.
The uwsgi.ini has been changed to use python-path and wsgi directives instead of the mount and force-script-name directives

karol

Went over the first post, still works in Sep 2024, thanks.