Deploy a FastAPI Application on DjaoDjin

In this tutorial, we will see how to run an application built with the Python/FastAPI framework behind a login page on the DjaoDjin hosting service.

Prerequisites:

• URL for a Website hosted on DjaoDjin (ex: livedemo.djaoapp.com) - Register
• Access rules configured to forward HTTP requests to the application logic server - ex: Deploy an image from a GitHub Packages registry

Notes on command line snippets

On command line snippets, lines starting with a $ character indicate a shell prompt, or a command for you to type. Lines that do not start with a $ character show a sample output from that command. Example:

$ whoami
ec2-user

Text edits within source files are shown in universal diff format with lines preceded by a '-' sign to be removed and lines preceded by a '+' sign to be added. Example:

 def set_default_profile():     # This line for context, to be kept as-is
-    profile = 'abc'            # This line to be removed
+    profile = 'cde'            # This line to be added
     return profile             # This line for context, to be kept as-is

The full source code for this tutorial is available on GitHub.

Setting up

First we will create a skeleton FastAPI application following FastAPI Getting Started.

Make sure you have an up-to-date version of Python installed, then run the following command in your command line (without the $ sign). This will setup a Python virtual environment and install the prerequisites to run your application locally as a ASGI (Web) server.

$ python -m venv .venv
$ source .venv/bin/activate
$ pip install fastapi "uvicorn[standard]" PyJWT
``

We will need `PyJWT` later to decode the session data attached by the DjaoDjin
session proxy to the HTTP request.

Create a file `main.py` with:

``` {.python title="main.py"}
from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}

Run the server with:

$ uvicorn main:app --reload
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

In another console window, we fetch the root API endpoint we declared earlier from the running FastAPI server.

$ curl http://127.0.0.1:8000
{"Hello":"World"}

Everything looks to be working OK up to this point.

Create and upload a Docker image to your favorite container registry, and deploy it to DjaoDjin's infrastructure (ex: Deploy an image from a GitHub Packages registry), or forward HTTP requests to a server you manage yourself.

Once you visit your Website on DjaoDjin (ex: https://livedemo.djaoapp.com), and you retrieve the {"Hello":"World"} response, it is time to decode session data for authenticated users.

Decoding session data

DjaoApp handles accounts, billing and access control pages, forwarding other HTTP requests to an application service as setup through access rules (see Overview of the HTTP pipeline). We just have to retrieve the authenticated user information in the application logic server now.

The session data is encoded as a JWT in the Authorization HTTP header. We thus replace our previous sample implementation returning 'Hello World' by the following code.

from typing import Annotated

import jwt
from fastapi import FastAPI, Header

DJAODJIN_SECRET_KEY = "**key downloaded from Rules dashboard**"
JWT_ALGORITHM = 'HS256'

app = FastAPI()


@app.get("/")
def read_root(authorization: Annotated[str | None, Header()] = None):
    session_key = None
    session_data = {}
    if authorization:
        jwt_values = authorization.split(' ')
        if (len(jwt_values) > 1 and
            jwt_values[0].lower() == 'bearer'):
            session_key = jwt_values[1]
    if session_key:
        try:
            session_data = jwt.decode(
                session_key,
                DJAODJIN_SECRET_KEY,
                algorithms=[JWT_ALGORITHM])
        except jwt.exceptions.PyJWTError:
            pass
    return session_data

Here we need to make sure DJAODJIN_SECRET_KEY is set to the value downloaded from the site Rules dashboard in order to decode sessions properly.

Et voila!