Python (Django, Flask, etc.)

Note: This document only applies to student groups with virtual hosts who have applied for apphosting. For normal user accounts or for groups without apphosting, you'll want to host with FastCGI instead. See our instructions for Django or Flask.

You will want to deploy your application using a virtualenv so that you can easily install and manage dependencies and versions.

Setting up a virtualenv

1. Create a directory for your app to live in:

   mkdir -p ~/myapp
   cd ~/myapp
   

2. Set up a virtualenv:

   virtualenv venv
   

3. Activate the virtualenv:

   . venv/bin/activate
   

   You should do this step every time before running your app or managing installed packages.

4. Copy your code to ~/myapp/src or similar, and install any dependencies using pip.

Installing gunicorn

We recommend using gunicorn to serve your application. After activating your virtualenv, install it with pip install gunicorn.

Note that you may see a warning about a syntax error. As long as the output ends in "Successfully installed gunicorn", it's safe to ignore this.

Preparing your app to be supervised

Create a file at ~/myapp/run with content like:

#!/bin/bash -e
. ~/myapp/venv/bin/activate
PYTHONPATH=~/myapp/src:$PYTHONPATH \
    exec gunicorn -w 2 -b unix:/srv/apps/$(whoami)/$(whoami).sock \
    --log-file - main:app

Replace main:app with the module containing the app, and name of your app, then make run executable:

chmod +x ~/myapp/run

Test executing the run script. You should be able to access your website while running it (or see any errors in your terminal).

Supervise your app with systemd

Cool, your app works. Set up systemd to supervise your app (so that it starts and restarts automatically).

Bonus Gunicorn tip: reloading your app

Gunicorn will reload your app if you send it SIGHUP. You can teach systemd that fact by adding the following line under [Service] in your systemd unit file:

ExecReload=/bin/kill -HUP $MAINPID

and then running systemctl --user daemon-reload. After that, you can use systemctl to reload your app:

systemctl --user reload myapp

Suggestions/improvements?

If you have a better way to host Python-based apps on the app server (or a suggestion for how we could improve this documentation), send us an email!