⚡ Serverless REST API on AWS with FastAPI ⚡

Hi there! 👊

In this article, I will explain you how to deploy, in minutes, FastAPI on AWS using Serverless.

As usual in all my articles, you will find at the end a link to a working example on my Github.

Pre-requisites

I assume you have at least Python 3.7+ and npm installed.

Install and configure AWS CLI

You need to install the AWS CLI and configure your credentials. You can follow this link for instructions.

Install Serverless Framework

Then you will have to install the Serverless framework via npm. See instructions here.

FastAPI Application

Build the application

First of all, we will build our FastAPI application. Add fastapi dependency in your requirements.txt and install it.
Then you can create your FastAPI application:

from fastapi import FastAPI
from starlette.middleware.cors import CORSMiddleware
from fastapi_aws_starter_kit.routers.health_check_api import router as hc_router
from fastapi_aws_starter_kit.config import PROJECT_NAME, API_VERSION

# Declare the application
app = FastAPI(title=PROJECT_NAME, debug=False, version=API_VERSION)


app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)


@app.get(path="/health", description="Health check")
def health_check():
    return {"status": "OK"}


app.include_router(hc_router)

Deploy FastAPI on AWS

To deploy our API in AWS, we will leverage API Gateway and Lambda services and use Serverless framework capabilities to easily create all resources we need.

Lambda handler with Mangum

In order to build the handler for our Lambda which will be called by our API Gateway, we will use Mangum which is an ASGI adapter for API Gateway and Lambda (perfect for our FastAPI application 🍾)

Add mangum to your dependencies and build the handler as follow:

from mangum import Mangum
from fastapi_aws_starter_kit.fastapi_app import app

handler = Mangum(app=app)

Configure serverless.yaml

Serverless configuration is pretty easy, here is what I did as a simple example:

org: cox65
app: fastapi-aws-starter-kit
service: fastapi-aws-starter-kit
package:
  individually: true
provider:
  name: aws
  runtime: python3.12
  region: eu-west-1
  httpApi:
    cors: true
  timeout: 10
  memorySize: 128
plugins:
  - serverless-python-requirements
  - serverless-offline
functions:
  app:
    package:
      patterns:
        - "fastapi_aws_starter_kit/**"
    handler: fastapi_aws_starter_kit.handler.handler
    events:
      - http:
          method: any
          path: /{proxy+}
          cors: true
custom:
  pythonRequirements:
    dockerizePip: true

As you can see I’m using 2 plugins:

• serverless-python-requirements: It will bundle your python dependencies specified in your requirements.txt

• serverless-offline: It will allow to run our infrastructure locally by running sls offline command.

Deploy your API

To deploy your API on AWS, you just need to perform:

sls deploy

Run your API in local

If you want to run your API in local, you have two options.
Either you can run an uvicorn web server like this:

import os
import uvicorn

if __name__ == "__main__":
    uvicorn.run(
        "fastapi_app:app",
        host="127.0.0.1",
        port=5000,
        reload=True,
    )

Either, and this what I recommend as we are using Serverless, you can use serverless-offline plugin I just mentionned before.

    ➜ sls offline
    Running "serverless" from node_modules
    Using local credentials. Add provider credentials via dashboard: https://app.serverless.com//providers

    Starting Offline at stage dev (eu-west-1)

    Offline [http for lambda] listening on http://localhost:3002
    Function names exposed for local invocation by aws-sdk:
               * app: fastapi-aws-starter-kit-dev-app

       ┌───────────────────────────────────────────────────────────────────────┐
       │                                                                       │
       │   ANY | http://localhost:3000/{proxy*}                                │
       │   POST | http://localhost:3000/2015-03-31/functions/app/invocations   │
       │                                                                       │
       └───────────────────────────────────────────────────────────────────────┘

    Server ready: http://localhost:3000 🚀

And that’s it ! 🚀

FastAPI AWS Starter Kit

Here the the repository related to this article:
GitHub - DevWaveX/fastapi-aws-starter-kit: Starter kit to deploy FastAPI as an AWS serverless…

I hope you enjoyed reading this article and that it will help you in your next projects ! 🤘

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