Host a Serverless Flask App on Vercel

Flask is a popular Python web framework that makes it simple to create web applications and API's in a short period of time. If you've created a Flask app and are worried about configuring a server as Heroku's free plan is no more, then worry not; you can run Flask as a serverless function on Vercel (yes, you have heard it right; we are gonna deploy a Flask app on Vercel).

Prerequisites

Before we begin, you should have the following things set up:

• A Vercel account. You can sign up for a free account at vercel.com.
• The Vercel CLI (Command Line Interface) installed on your computer. You can install the Vercel CLI by running the following command in your terminal.

npm install -g vercel

Deploying the Flask App

Open up your favourite code editor and initialize the following files and folders in the below order:

project
│───vercel.json   
│───requirements.txt
└───api
     │───app.py

In the app.py file. Lets us write a basic Hello World program which you can modify as per your needs.

from flask import Flask
app = Flask(__name__)

@app.get('/')
def hello_world():
    return "Hello, World!"

In the requirements.txt, write

Flask

It is the only PyPi package we need. The Web Server Gateway Interface (WSGI) is provided automatically by Vercel during the runtime.

The vercel.json file contains the configuration for this project.

A Sample Configuration for Flask is:

{
  "routes": [
    {
      "src": "/(.*)",
      "dest": "api/app.py"
    }
  ]
}

The above code routes any request to the original page to the Flask Server which was written in app.py.

Now deploy the Flask app onto vercel by running:

vercel deploy --prod

Follow the prompts asked and Vercel will then build and deploy your app, and you will be provided with a URL where you can access your app. You can also access your website's URL by going to your Vercel dashboard.

The URL for my Flask App which I have made using above steps is vercel-flask-demo-one.vercel.app

Additional Configuration

If you want to customize the way your Flask app is deployed, you can add additional options to the vercel.json file. For example, you can specify the Python version to use, or add environment variables to your app, specify the maximum execution time and the memory for a request etc.

Bonus

If you are thinking about running FastAPI in Vercel then its absolutely possible. Just replace Flask in requirements.txt with fastapi and Vercel will automatically use the corresponding ASGI to serve it.

You can read more on: Python Runtimes

I have created this blog post to show that it is possible to deploy common Python Web apps like Flask and FastAPI on Vercel by use of Serverless Functions as many people just use Vercel for hosting their Frontends and never fully explore it. In the next article, I will show you how you can host Serverless Bots on Vercel.

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