2 · User Request Lifecycle

This diagram follows one request through the whole production AI system — from the user, through FastAPI, LangServe, LangGraph and Bedrock, back to a streamed response.

How it works

1. 1User: asks a question, uploads a file or triggers an action.
2. 2FastAPI: handles API endpoints, request validation and dependency injection.
3. 3LangServe: exposes LangChain chains as APIs (invoke, stream, batch).
4. 4LangGraph: orchestrates steps, state and conditional routing.
5. 5Bedrock (Claude/Nova/Titan): generates the response, which is streamed back.

Key points

• The entry pipeline handles authentication, rate limiting and streaming before the LangChain stack.
• After the model, post-processing formats output, stores memory and adds observability.
• FastAPI + LangServe + LangGraph + Bedrock work together as one secure, streaming-ready system.
• Everything is observable via LangSmith and CloudWatch.

Why it matters

Understanding the request lifecycle shows where security, streaming and orchestration each live — essential for debugging and building reliable AI APIs.

Frequently asked questions

Where does authentication happen?

In the FastAPI entry pipeline, before the request reaches the LangChain stack.

How are responses streamed?

Via server-sent events from LangServe, so tokens arrive in real time.