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 the API key required for the API

Solution overview
Build FastAPI as a lambda funnction handler
Deploy
Test API
Conclusion

🚀 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 serve 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

```plaintext @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`

    ```plaintext
    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

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