Flask§

To run apps built with the Flask web framework using Unit:

1. Install Unit with a Python 3 language module.

2. Create a virtual environment to install Flask’s PIP package:

   $ cd /path/to/app/
   $ python3 --version
         Python 3.Y.Z
   $ python3 -m venv venv
   $ source venv/bin/activate
   $ pip install Flask
   $ deactivate
   

   Warning

   Create your virtual environment with a Python version that matches the language module from Step 1 up to the minor number (3.Y in this example). Also, the app type in Step 5 must resolve to a similarly matching version; Unit doesn’t infer it from the environment.

3. Let’s try a basic version of the quickstart app, saving it as /path/to/app/wsgi.py:

   from flask import Flask
   app = Flask(__name__)
   
   @app.route("/")
   def hello_world():
       return "Hello, World!"
   

4. Run the following command so Unit can access the application directory:

   # chown -R unit:unit /path/to/app/
   

   Note

   The unit:unit user-group pair is available only with official packages, Docker images, and some third-party repos. Otherwise, account names may differ; run the ps aux | grep unitd command to be sure.

   For further details, including permissions, see the security checklist.

5. Next, prepare the Flask configuration for Unit (use real values for type, home, and path):

   {
       "listeners": {
           "*:80": {
               "pass": "applications/flask"
           }
       },
   
       "applications": {
           "flask": {
               "type": "python 3.Y",
               "path": "/path/to/app/",
               "home": "/path/to/app/venv/",
               "module": "wsgi",
               "callable": "app"
           }
       }
   }
   

6. Upload the updated configuration. Assuming the JSON above was added to config.json:

   # curl -X PUT --data-binary @config.json --unix-socket \
          /path/to/control.unit.sock http://localhost/config/
   

   Note

   The control socket path may vary; run unitd -h or see Startup and Shutdown for details.

   After a successful update, your app should be available on the listener’s IP address and port:

   $ curl http://localhost
   
         Hello, World!