.. author:: Christian Macht <https://github.com/cmacht/>

.. tag:: lang-python

.. tag:: web

Logo

.. tag_list::

FastAPI is a modern, async web-framework for building APIs with Python 3.6+ making use of type hints. It is a microframework, in many ways quite similar to Flask and uses the MIT license.

We are creating a very basic proof-of-concept API that will do a calculation and return the result as valid JSON.

[isabell@stardust ~]$ mkdir ~/fastapi
[isabell@stardust ~]$

Create a file ~/fastapi/main.py with the following content:

#!/usr/bin/env python3.11
import fastapi
import uvicorn

api = fastapi.FastAPI()

@api.get('/')
def calculate():
  answer = 24 + 18
  return {'answer': answer}

# To test this app locally, uncomment this line:
# uvicorn.run(api, host="localhost", port=8000)

To install the packages your application depends on, you want to use a virtual environment that is isolated from the system's Python packages. FastAPI requires Python 3.6+ but we are going to use the latest version available, which is currently Python 3.11:

[isabell@stardust ~]$ cd ~/fastapi
[isabell@stardust fastapi]$ python3.11 -m venv venv
[isabell@stardust fastapi]$ source venv/bin/activate
(venv) [isabell@stardust fastapi]$

In your virtual environment, install the dependencies we are using in main.py:

(venv) [isabell@stardust fastapi]$ pip install fastapi uvicorn
(venv) [isabell@stardust fastapi]$

While uvicorn handles the asynchronous side of FastAPI, we want gunicorn as a well-tested and production-ready solution to run and manage multiple uvicorn workers. Install it with two dependencies in your virtual environment:

(venv) [isabell@stardust fastapi]$ pip install gunicorn uvloop httptools
(venv) [isabell@stardust fastapi]$

You can deactivate the virtual environment context like this:

(venv) [isabell@stardust fastapi]$ deactivate
[isabell@stardust fastapi]$

Incoming https requests are routed through :manual:`nginx <background-http-stack>` to a :manual:`web backend <web-backends>` where our application server is listening. Let's get this working:

First, we are telling gunicorn to spin up several uvicorn processes and listen on port 8000 for incoming requests. Create the config file ~/fastapi/conf.py:

import os
app_path = os.environ['HOME'] + '/fastapi'

# Gunicorn configuration
wsgi_app = 'main:api'
bind = ':8000'
chdir = app_path
workers = 4
worker_class = 'uvicorn.workers.UvicornWorker'
errorlog =  app_path + '/errors.log'

This is a minimal working example based on gunicorn's example config, you can find a comprehensive list of options here.

Next, create a configuration for supervisord in ~/etc/services.d/fastapi.ini:

[program:fastapi]
directory=%(ENV_HOME)s/fastapi
command=%(ENV_HOME)s/fastapi/venv/bin/gunicorn --config %(ENV_HOME)s/fastapi/conf.py

This concludes the setup. Point your browser to :manual:`your url <web-domains>` and check that everything is running correctly.

.. author_list::