Deploying FastAPI on AWS Lambda with Mangum

AWS Lambda runs code on demand and bills only while it executes. FastAPI is an ASGI application, and Lambda speaks in events — so we need an adapter between the two. That adapter is Mangum.

This guide deploys a project using two separate archives: the application code, and its dependencies packaged as a Lambda layer. Keeping them apart means code-only changes upload in seconds, and the layer can be shared between functions.

Before you start

You’ll need a FastAPI project and an AWS account with access to Lambda and S3. The examples use a project called sample-fastapi-project, an S3 bucket called sample-fastapi-s3, and a function called sample-fastapi-lambda.

Prepare the project

Isolate the project’s dependencies in a virtual environment and install them:

python3 -m venv venv
source venv/bin/activate        # Windows: .\venv\Scripts\activate
pip install -r requirements.txt

Add Mangum and record it in your requirements:

pip install mangum
pip freeze > requirements.txt

Then wrap the application. The handler object is what Lambda will invoke:

from fastapi import FastAPI
from mangum import Mangum

app = FastAPI()


@app.get("/health")
def health():
    return {"status": "ok"}


handler = Mangum(app)