FastAPI

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

1. Install Unit with a Python 3.6+ language module.

2. Create a virtual environment to install FastAPI’s PIP package, for instance:

   $ 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 fastapi
   $ 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 version of a tutorial app, saving it as /path/to/app/asgi.py:

   from fastapi import FastAPI
   
   app = FastAPI()
   
   @app.get("/")
   async def root():
       return {"message": "Hello, World!"}
   

   Note:
   For something more true-to-life, try the RealWorld example app; just install all its dependencies in the same virtual environment where you’ve installed FastAPI and add the app’s environment {ref}variables <configuration-apps-common> like DB_CONNECTION or SECRET_KEY directly to the app configuration in Unit instead of the .env file.

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):

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

   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 FastAPI configuration for Unit (use real values for type, home, and path):

   {
      "listeners": {
         "*:80": {
            "pass": "applications/fastapi"
         }
      },
      "applications": {
         "fastapi": {
            "type": "python 3.Y",
            "type_comment": "Must match language module version and virtual environment version",
            "path": "/path/to/app/",
            "path_comment": "Path to the ASGI module",
            "home": "/path/to/app/venv/",
            "home_comment": "Path to the virtual environment, if any",
            "module": "asgi",
            "module_comment": "ASGI 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:

   # 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
      

   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!
   

   Alternatively, try FastAPI’s nifty self-documenting features: