Building a Production-Ready LLM Service with FastAPI

This title was summarized by AI from the post below.

Building a production-grade LLM service from scratch — Days 2 & 3 🧵 This week I moved past AI demos and started treating LLM integration as real infrastructure. Two endpoints, and a lot of decisions about what "production-ready" actually requires. Day 2 - A properly structured FastAPI service Wrapped the Gemini API in a /chat endpoint, with the focus on doing it correctly rather than just getting output: → Async-first design (async def + await) so the server handles concurrent load without blocking → Pydantic models validating every request and response, so invalid input never reaches business logic → pydantic-settings for configuration - secrets in environment variables, never hardcoded → A clean, maintainable layout: app/, config.py, routes/, services/, schemas/ The endpoint returning a response was the easy part. The structure that makes it maintainable and testable was the real work. Day 3 - Streaming, and handling failure gracefully An 8-second wait for a full response feels broken; streaming the same response feels responsive - even though total latency is identical. That UX gap is worth engineering for. Built /chat/stream using Server-Sent Events and FastAPI's StreamingResponse, with three event types: → delta - text chunks as they're generated → usage - token counts on completion → error - upstream failures surfaced cleanly within the stream I also tested the failure path most demos ignore: what happens when a client disconnects mid-stream? Left unhandled, the server keeps generating billable tokens for a client that's no longer listening. The fix - if await request.is_disconnected(): break - propagates cancellation down to the SDK's connection to Google, so ungenerated tokens are never billed. At scale (100k requests/day, ~10% disconnect rate, 500-token responses), that's a meaningful cost saving. Finally, I built a lightweight JS demo to experience the result from the user's side - a useful reminder that latency is as much about perception as raw speed. Two days, two endpoints, and a clearer sense of the gap between a working prototype and a production service. #AI #MachineLearning #Python #FastAPI #LLM #SoftwareEngineering #BackendDevelopment

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