langchain-deploy-integration

name	langchain-deploy-integration
description	Deploy a LangChain 1.0 / LangGraph 1.0 app to Cloud Run, Vercel, or LangServe correctly — with timeouts sized for chain length, cold-start mitigation, SSE anti-buffering headers, and Secret Manager over .env. Use when prepping a first production deploy, debugging a stream that hangs behind a proxy, or diagnosing p99 latency spikes. Trigger with "langchain deploy", "langchain cloud run", "langchain vercel python", "langchain langserve", or "langchain docker".
allowed-tools	Read, Write, Edit, Bash(docker:*), Bash(gcloud:*), Bash(vercel:*)
version	2.5.0
license	MIT
author	Jeremy Longshore <[e-mail]>
tags	["saas","langchain","langgraph","python","langchain-1.0","deployment","cloud-run","vercel","langserve"]
compatibility	Designed for Claude Code

LangChain Deploy Integration (Python)

Overview

An engineer ships a working LangGraph agent to Vercel. Every non-trivial request returns FUNCTION_INVOCATION_TIMEOUT. The Python runtime on Vercel defaults to a 10-second cap (P35) — a three-tool agent with one RAG round easily runs 20-40s. Local dev never exposed the wall because uvicorn on a laptop has no timeout. Two fixes apply together and each is load-bearing:

// vercel.json — the baseline cap bump (Pro plan max is 60s, Enterprise 900s)
{ "functions": { "api/chat.py": { "maxDuration": 60 } } }

# app/api/chat.py — stream the response so partial output arrives before the cap
from fastapi.responses import StreamingResponse

@app.post("/api/chat")
async def chat(req: ChatRequest):
    async def gen():
        async for chunk in chain.astream(req.input):
            yield f"data: {chunk.model_dump_json()}\n\n"
    return StreamingResponse(gen(), media_type="text/event-stream",
                             headers={"X-Accel-Buffering": "no"})

The maxDuration: 60 raises the Vercel-imposed wall; streaming reduces time-to-first-byte to under a second so the user sees progress even on a 40-second completion. Once the Vercel cap is fixed, the next three walls are: Cloud Run cold starts ( p99 on Python + LangChain — P36), secrets leaking via (P37), and SSE streams hanging because Nginx / Cloud Run buffer the final chunk (P46).