HOWTO run Flask under uwsgi on Opalstack

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.

dhakajack

I recently came to Opalstack and was lost at the "Create a new uwsgi app via your Opalstack dashboard" because I saw various stacks like Django, but not an option for base install of uWSGI/Flask. I opened a help ticket and got an immediate reply, which worked the first time around, so here it is. I was told that bare uWSGI apps are only available on the older CentOS 7 servers, and that the application options looked different to me because I was on one of the newer Almalinux 9 servers.

Options for installing uWSGI/Flask are either to use a listed application like Django and then remove the Django components or manually setup following these instructions:

Copy your API token value from https://my.opalstack.com/tokens/
Go to https://my.opalstack.com/apps/ and click the </> icon for your app's shell user, then copy the "ID" field for the shell user.
Log in to SSH as the shell user and run the following command, replacing TOKEN with your API token value, ID with the shell user ID and 'NAME' with the name for the new app. Note that this is all a single line:

curl -H "Authorization:Token TOKEN" -H "Content-Type: application/json" -X POST https://my.opalstack.com/api/v1/app/create/ -d '[{"type":"CUS", "name":"NAME", "osuser":"ID", "installer_url":"https://raw.githubusercontent.com/opalstack/installers/refs/heads/master/core/uwsgi/install.sh", "json":{"gzip":true}}]'

That will run an API request to create the new app.

Watch https://my.opalstack.com/apps/ until the new app status is "Ready".

Run the following commands as the app's shell user:

    cd ~/apps/NAME
    rm -rf env
    python3.13 -m venv env
    source env/bin/activate
    pip install uwsgi flask
    ./start

At that stage, the new app will be running with a basic WSGI setup. You can then upload or create your Flask project directory, update uwsgi.ini to serve it, and restart the app using its stop and start scripts.