FastApi With AWS Serverless powered by CDK Typescript

Abstract

• Deploy FastAPI in a Lambda function that is fronted by an HTTP API in API Gateway, you can enable API key required for the API

Table Of Contents

🚀 Solution overview

• Use AWS APIGW to build a simple API server with lambda integration

• APIGW route paths such as /api/v1/ and /chat_gpt/ require API key (with usage plan)

• The lambda function contains FastApi code to serves API requests and responses.

• Let’s see the stack relationships

  

🚀 Build FastAPI as a lambda funnction handler

• Lambda handler source code

  ➜  simple-serverless-fastapi tree src/lambda-handler
  src/lambda-handler
  ├── api
  │   └── api_v1
  │       ├── api.py
  │       └── endpoints
  │           └── users.py
  ├── main.py
  └── requirements.txt
  
  4 directories, 4 files

• Direct route paths include / and chat_gpt

  @app.get("/")
  async def root():
      return {"message": "FastAPI running in a Lambda function"}
  
  
  @app.get("/chat_gpt/")
  async def read_chatgpt(question: str = None):
      return {"message": f"We got question: {question}"}

• Restructure FastAPI Routing for developing API and optimize source code by using APIRouter

  src/lambda-handler/api
  └── api_v1
      ├── api.py
      └── endpoints
          └── users.py

  from api.api_v1.api import router as api_router
  app.include_router(api_router, prefix="/api/v1")

• For the lambda function handler, we use Mangum python module which is an adapter for running ASGI applications in AWS Lambda to handle Function URL, API Gateway, ALB, and Lambda@Edge events.

• For building API Docs, one must set the following parameters in FastApi() constructor to resolve /openapi.json correctly

  • For API URL using APIGW stage URL, set root_path equal to the API stage name, eg. root_path=/AppAPI
  • For API custom domain

    docs_url='/docs',
    openapi_url='/openapi.json',

🚀 Deploy

• For production, building CDK pipeline for this is the best practice.

• For the demo, I run cdk deploy manually

  ➜  simple-serverless-fastapi cdk deploy
   ✅  SimpleFastApiServerless
  
  ✨  Deployment time: 72.44s

• The API GW and method request

  

• Custom domain mapped to the API

  

🚀 Test API

• Open API Docs

  

• Call /chat_gpt with API key and query question

  ➜  simple-serverless-fastapi curl -X GET -H "Content-Type: application/json" -H 'x-api-key: 6sUnYj8PAw8MKu8O6FqSw1kf1clmC0Fx8ilQhVeO' https://chatgpt.simflexcloud.com/chat_gpt/ -d 'question=how%20are%20you' -G
  {"message":"We got question: how are you"}

🚀 Conclusion

• We created a FastAPI application using AWS Serverless. The user must provide the API key to query request and the API key is associated with the usage plan where we can specify who can access the deployed API stages and methods, and optionally sets the target request rate to start throttling requests.

References:

• Simple Serverless FastAPI with AWS Lambda