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 Flasks`s PIP package, for instance:

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   $ cd /path/to/app/  # Path to the application directory; use a real path in your configuration
   $ python --version  # Make sure your virtual environment version matches the module version
         Python X.Y.Z  # Major version, minor version, and revision number
   $ python -m venv venv  # Arbitrary name of the virtual environment
   $ source venv/bin/activate  # Name of the virtual environment from the previous command
   $ pip install Flask
   $ deactivate
   

   $ cd /path/to/app/  # Path to the application directory; use a real path in your configuration
   $ python --version  # Make sure your virtual environment version matches the module version
         Python X.Y.Z  # Major version, minor version, and revision number
   $ python -m venv venv  # Arbitrary name of the virtual environment
   $ source venv/bin/activate  # Name of the virtual environment from the previous command
   $ 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 (X.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:

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   from flask import Flask
   app  = Flask(__name__) # Callable name used in Unit's condfiguration
   
   @app.route("/")
   def hello_world():
       return "Hello, World!"

   from flask import Flask
   app  = Flask(__name__) # Callable name used in Unit's condfiguration
   
   @app.route("/")
   def hello_world():
       return "Hello, World!"

4. Change ownership:

   Run the following command (as root) so Unit can access the application directory (If the application uses several directories, run the command for each one):

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   # chown -R unit:unit /path/to/app/  # User and group that Unit's router runs as by default
      

   # chown -R unit:unit /path/to/app/  # User and group that Unit's router runs as by default
      

   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 [ app ] configuration for Unit (use real values for type, home, and path):

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   {
      "listeners": {
         "*:80": {
            "pass": "applications/flask"
         }
      },
      "applications": {
         "flask": {
            "type": "python 3.Y",
            "type_comment": "Must match language module version and virtual environment version",
            "path": "/path/to/app/",
            "path_comment": "Path to the WSGI module",
            "home": "/path/to/app/venv/",
            "home_comment": "Path to the virtual environment, if any",
            "module": "wsgi",
            "module_comment": "WSGI module filename with extension omitted",
            "callable": "app",
            "callable_comment": "Name of the callable in the module to run"
         }
      }
   }

   {
      "listeners": {
         "*:80": {
            "pass": "applications/flask"
         }
      },
      "applications": {
         "flask": {
            "type": "python 3.Y",
            "type_comment": "Must match language module version and virtual environment version",
            "path": "/path/to/app/",
            "path_comment": "Path to the WSGI module",
            "home": "/path/to/app/venv/",
            "home_comment": "Path to the virtual environment, if any",
            "module": "wsgi",
            "module_comment": "WSGI module filename with extension omitted",
            "callable": "app",
            "callable_comment": "Name of the callable in the module to run"
         }
      }
   }

6. Upload the updated configuration.

   Assuming the JSON above was added to config.json. Run the following command as root:

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   # curl -X PUT --data-binary @config.json --unix-socket \
         /path/to/control.unit.sock \  # Path to Unit's control socket in your installation
         http://localhost/config/      # Path to the config section in Unit's control API
      

   # curl -X PUT --data-binary @config.json --unix-socket \
         /path/to/control.unit.sock \  # Path to Unit's control socket in your installation
         http://localhost/config/      # Path to the config section in Unit's control API
      

   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:

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   $ curl http://localhost
   
         Hello, World!
   

   $ curl http://localhost
   
         Hello, World!