Do you want a simple way to deploy an python FastAPI in AWS Lambda ? There is an simple way to do this with Magnum.

First, let’s add FastAPI, magnum and SAM cli, in requirements.txt file:

fastapi
mangum
aws-sam-cli

Next, let’s code a simple FastAPI sample app:

from fastapi import FastAPI
from mangum import Mangum

app = FastAPI()

@app.get("/high-scores")
async def high_scores():
    return {"scores": [100, 200, 300]}

@app.post("/insert-score")
async def insert_score(data: dict):
    return {"status": "success", "data": data}

lambda_handler = Mangum(app, lifespan="off")

if __name__ == "__main__":
    import uvicorn
    uvicorn.run("app:app", port=5000, log_level="info", reload=True)

Next, let’s setup SAM with a template.yml file:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  MangumTestFunction:
    Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
    Properties:
      # CodeUri: hello_world/
      Handler: app.lambda_handler
      Runtime: python3.12
      Architectures:
        - x86_64
      Events:
        HelloWorld:
          Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
          Properties:
            Path: /{proxy+}
            Method: ANY

Outputs:
  # ServerlessRestApi is an implicit API created out of Events key under Serverless::Function
  # Find out more about other implicit resources you can reference within SAM
  # https://github.com/awslabs/serverless-application-model/blob/master/docs/internals/generated_resources.rst#api
  HelloWorldApi:
    Description: "API Gateway endpoint URL for Prod stage for Hello World function"
    Value: !Sub "https://${ServerlessRestApi}.execute-api.${AWS::Region}.amazonaws.com/Prod/"
  HelloWorldFunction:
    Description: "Hello World Lambda Function ARN"
    Value: !GetAtt MangumTestFunction.Arn
  HelloWorldFunctionIamRole:
    Description: "Implicit IAM Role created for Hello World function"
    Value: !GetAtt MangumTestFunctionRole.Arn

This will create the AWS Lambda and API Gateway to expose the your API to the world.

Now lets build and deploy the function:

sam build -u
sam deploy --guided

If all it’s ok, the result should look something like this:

logs

Now we can call the API using curl for example:

curl -X GET https://<ID>.execute-api.eu-central-1.amazonaws.com/Prod/high-scores

With the response

{"scores":[100,200,300]}