Serverless FastAPI with AWS Lambda

Mangum allows us to wrap the API with a handler that we will package and deploy as a Lambda function in AWS. Then using AWS API Gateway we will route all incoming requests to invoke the lambda and handle the routing internally within our application.

Install Mangum

pip install mangum

Setup AWS Resources

This tutorial should fall under the AWS free-tier to create, however continued usage of these resources will have associated costs.

Create S3 Bucket

Navigate to S3 in the AWS console and click Create Bucket.
Give it a name and click Create. In this example we're going to call it serverless-fastapi-lambda-dev

Upload Zip File

Before we can create the lambda we need to package up our existing FastApi app so it's ready for AWS Lambda.

The lambda won't be running in the virtual environment and will only be running one command (which we will determine when we create it) which will be main.handler So we need to install all the dependencies within the zip file since it won't be running pip install like we did locally.

Package Lambda

Inside your terminal from the root directory of your project, CD into the Python Site Packages folder.

cd env/lib/python3.7/site-packages

Then zip up the contents into the root of the project.

cd env/lib/python3.7/site-packages

zip -r9 path/to/root/of/project/function.zip

CD back into the root of the project.

cd path/to/root/of/project

Next we need to add the contents of the app folder so let's add that into the zip file.

zip -g ./function.zip -r app

Upload Zip File to S3

Go inside the S3 bucket you just created and click Upload.
Add your zip file through the interface that pops up and and click Upload.

Final Steps

Create AWS Lambda
Update Handler
Test FastAPI Lambda
Create API Gateway
Create Resource
Deploy Lambda Proxy API

Summary

That's it! We Created a FastAPI application and converted it to an AWS Lambda. Then we setup API Gateway to route all requests to our Lambda proxy.

References

Simple Serverless FastAPI with AWS Lambda - [https://www.deadbear.io/simple-serverless-fastapi-with-aws-lambda/]