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Help:Toolforge/My first Python ASGI tool

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Prior to Build Service, it was not possible to deploy Python ASGI applications to Toolforge due to the Webservice framework applying the uWSGI application server onto all Python web services. As Build Service lets the user specify the web server they want to use in their application, it is now possible to deploy ASGI applications in addition to WSGI.

This stub webservice is designed to get a sample Python ASGI application deployed onto Toolforge using the new Build Service, as quickly as possible. The application is written using the FastAPI framework.

The guide will teach you how to:

  • Create a new tool
  • Build and deploy a Python 3 ASGI webservice using Toolforge Build Service.

Getting started

Prerequisites

Skills

Accounts

Step-by-step guide

Step 1: Create a new tool account

  1. Follow the Toolforge quickstart guide to create a Toolforge tool and SSH into Toolforge.
    • For the examples in this tutorial, sample-python-buildpack-app is used to indicate places where your unique tool name is used in another command.
  2. Make sure to create a git repository for the tool, you can get one like this:
    1. Log into the toolforge admin page
    2. Select your tool
    3. On the left side panel, under Git repositories click create repository
    4. Copy the url in the Clone section
      1. There's a private url, that we will use to clone it locally, starting with "git": git@gitlab.wikimedia.org:toolforge-repos/sample-python-buildpack-asgi.git
      2. And a public one, that we will use to build the app in toolforge, starting with "https": https://gitlab.wikimedia.org/toolforge-repos/sample-python-buildpack-asgi.git

Step 2: Create a basic FastAPI ASGI application

The application we are going to build is a simple random quote generator that exposes an API. The quotes are fetched from an open-source third-party API which does not require authentication.

What is FastAPI?

FastAPI is a modern, high-performance web framework for building APIs with Python. Its key features include automatic data validation, serialization, and documentation using OpenAPI. It has asynchronous support which makes it suitable for high-concurrency applications such as ML-applications and data processing systems.

Let's get started creating the web application.

1. Clone your tool git repository

You will have to clone the tool repository to be able to add code to it, on your local computer (with git installed) you can run: 

laptop:~$ git clone git@gitlab.wikimedia.org:toolforge-repos/sample-python-buildpack-asgi.git
laptop:~$ cd sample-python-buildpack-asgi

This will clone our project from GitLab. For now, the folder is empty but it contains an already initialized git repository. We are ready to start.

2. Install the application dependencies

It is good practice to create a virtual environment for your Python project. There are several ways of doing so; use your preferred one. For an in-depth guide, see Python/Development Tools. 

laptop:~sample-python-buildpack-asgi$ pip install fastapi httpx 'uvicorn[standard]' gunicorn

Later, we will export our dependencies to a file called requirements.txt. This file is required for the Build Service to install our project's dependencies.

Optionally, if we want to specify a Python version, we can create a file called runtime.txt. If we don't, our project will install and use the latest Python version available to the software that builds our application image under the hood, currently 3.12.1. Here is how we could specify a different version: 

laptop:~sample-python-buildpack-asgi$ echo "python-3.10.2" > runtime.txt
The runtime.txt format is case-sensitive and must not include spaces. You must also specify the python- prefix and all three version number components: major, minor, and patch.

3. Create a basic ASGI application

app.py
# -*- coding: utf-8 -*-
#
# This file is part of the Toolforge Python ASGI tutorial
#
# Copyright (C) 2023 Slavina Stefanova and contributors
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

import httpx

from fastapi import FastAPI, HTTPException

app = FastAPI()


@app.get("/")
async def hello():
    return {"Hello": "World"}
App.py starts with a license header that places it under the GPLv3+ license.

Code on Toolforge must always be licensed under an Open Source Initiative (OSI) approved license. See the Right to fork policy for more information on this Toolforge policy.

We are now ready to run the application locally: 

laptop:~sample-python-buildpack-asgi$ uvicorn app:app --reload

You should now be able to navigate to http://127.0.0.1:8000 and see the hello world JSON. Nice! Let's add the code to fetch a random quote, and create an API endpoint for it.

app.py
# -*- coding: utf-8 -*-
#
# This file is part of the Toolforge Python ASGI tutorial
#
# Copyright (C) 2023 Slavina Stefanova and contributors
#
# This program is free software: you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the Free
# Software Foundation, either version 3 of the License, or (at your option)
# any later version.
#
# This program is distributed in the hope that it will be useful, but WITHOUT
# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

# more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

import httpx

from fastapi import FastAPI, HTTPException

app = FastAPI()

async def fetch_random_quote():
    '''Fetches a random quote from the Quotable API, an open-source API (https://github.com/lukePeavey/quotable).
    '''
    async with httpx.AsyncClient() as client:
        response = await client.get('https://api.quotable.io/random')
        if response.status_code == 200:
            return response.json()
        else:
            raise HTTPException(status_code=response.status_code, detail="Unable to fetch quote")


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


@app.get("/quote")
async def read_random_quote():
    quote_data = await fetch_random_quote()
    return quote_data

We now have a GET API endpoint called /quote. One of the really nice features of FastAPI is that it comes with built-in OpenAPI documentation. Try it out by navigating to http://127.0.0.1:8000/docs.

Step 3: Prepare the application for deployment

1. Create a requirements.txt file 

laptop:~sample-python-buildpack-asgi$ pip freeze > requirements.txt

Every time you add new dependencies to your project, this needs to be run anew.

NOTE: There's currently no other way to specify your dependencies, you can find some workaround in task T353762

2. Create the Procfile

The Procfile is based on heroku's procfile, though we don't support all it's features. For now, we only use the web entry point to get the command your server will be started with: 

laptop:~sample-python-buildpack-asgi$ cat > Procfile << EOF
web: gunicorn app:app -k uvicorn.workers.UvicornWorker --workers=4 --timeout 60 --bind 0.0.0.0
EOF

You can try this command locally. Note that it will default to using port 8000. If this port is already is use by another application, you can specify a different port for Gunicorn by changing the --bind argument, such as --bind 0.0.0.0:8080 to use port 8080 instead.

The --timeout argument isn't strictly necessary, but it can help when deploying more resource-intensive applications to Toolforge.

Understanding Uvicorn and Gunicorn in ASGI Applications

Uvicorn: Uvicorn is an ASGI server implementation, using uvloop and httptools. Primarily, it serves as an ASGI server for running asynchronous Python web applications built with frameworks like FastAPI or Starlette. It's known for its speed and efficiency in handling asynchronous operations.

Gunicorn with Uvicorn Workers: Gunicorn, traditionally a WSGI server for synchronous Python web applications, can be extended to support asynchronous applications by using Uvicorn workers. When used with Uvicorn workers (-k uvicorn.workers.UvicornWorker), Gunicorn manages multiple Uvicorn worker processes. This setup allows your FastAPI application to handle a higher load than what a single Uvicorn worker could manage on its own, providing a balance between Uvicorn's high performance in asynchronous tasks and Gunicorn's robust process management.

How They Work Together: In this configuration, Gunicorn acts as the main process manager, handling things like worker process scaling and network traffic distribution. Each worker process runs an instance of the Uvicorn server. This combination is ideal for production deployments of FastAPI applications, combining the concurrency benefits of Uvicorn and the process management strengths of Gunicorn.

3. Commit your changes and push 

laptop:~sample-python-buildpack-asgi$ git add .
laptop:~sample-python-buildpack-asgi$ git commit -m "First commit"
laptop:~sample-python-buildpack-asgi$ git push origin main
EOF


Build the image

Now we have to ssh to login.toolforge.org and start the build for the image: 

laptop:~sample-python-buildpack-aasi$ ssh login.toolforge.org  # or the equivalent with PuTTY
user@tools-sgebastion-10$ become sample-python-buildpack-asgi
tools.sample-python-buildpack-asgi@tools-sgebastion-10$ toolforge build start https://gitlab.wikimedia.org/toolforge-repos/sample-python-buildpack-asgi.git
You have to pass the public url of the git repository, otherwise it will not be able to clone it.
Wait for the build to finish

You can check the status of the build like this: 

tools.sample-python-buildpack-app@tools-sgebastion-10:~$ toolforge build show

You have to wait for the status to be ok(Succeeded).

Start the webservice
tools.sample-python-buildpack-asgi@tools-sgebastion-10$ toolforge webservice buildservice start --mount=none 
Starting webservice.

Once the webservice is started, navigate to https://sample-python-buildpack-asgi.toolforge.org in your web browser, and see a 'Hello World!' message. It might take a few minutes until it is reachable. Again, the API docs will be available at https://sample-python-buildpack-asgi.toolforge.org/docs

Notes

You can see the code used in this example here: https://gitlab.wikimedia.org/toolforge-repos/sample-python-buildpack-asgi

Troubleshooting

See Help:Toolforge/Build_Service#Troubleshooting.

See also

Communication and support

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Discuss and receive general support
Stay aware of critical changes and plans
Track work tasks and report bugs

Use a subproject of the #Cloud-Services Phabricator project to track confirmed bug reports and feature requests about the Cloud Services infrastructure itself

Read stories and WMCS blog posts

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