FastAPI vs. Node.js for High-Throughput Microservices

┌────────────────────────────────────────────────────────┐
│                   THE ARCHITECTURAL SPLIT              │
├──────────────────────────┬─────────────────────────────┤
│   Node.js (TypeScript)   │       Python FastAPI        │
├──────────────────────────┼─────────────────────────────┤
│ • Full-stack type sharing│ • Native GenAI & LLM tooling│
│ • Ultra-low I/O latency  │ • Rust-powered Pydantic v2  │
│ • Massive npm ecosystem  │ • Auto Swagger / OpenAPI    │
│ • Best for WebSockets/CRU│ • Best for AI/OCR/Data jobs │
└──────────────────────────┴─────────────────────────────┘

# main.py - FastAPI Microservice with Pydantic v2 Validation
from fastapi import FastAPI, HTTPException, Depends
from pydantic import BaseModel, Field
from typing import List, Optional
import time

app = FastAPI(
    title="KaamLabs Enterprise Engine",
    description="High-throughput operations API",
    version="2.0.0"
)

class GSTInvoiceItem(BaseModel):
    sku: str
    quantity: int = Field(gt=0, description="Quantity must be greater than zero")
    unit_price: float = Field(gt=0)
    hsn_sac: str

class InvoiceValidationRequest(BaseModel):
    vendor_gstin: str = Field(pattern=r"^[0-9]{2}[A-Z]{5}[0-9]{4}[A-Z]{1}[1-9A-Z]{1}Z[0-9A-Z]{1}
quot;)
    total_amount: float
    items: List[GSTInvoiceItem]

@app.post("/v1/invoices/validate", status_code=200)
async def validate_invoice(request: InvoiceValidationRequest):
    start_time = time.time()

    # 1. Calculate and verify mathematical tax correctness
    calculated_subtotal = sum(item.quantity * item.unit_price for item in request.items)
    expected_total = round(calculated_subtotal * 1.18, 2)

    if abs(expected_total - request.total_amount) > 1.00:
        raise HTTPException(
            status_code=422,
            detail=f"GST calculation mismatch. Expected ₹{expected_total}, received ₹{request.total_amount}"
        )

    execution_time_ms = round((time.time() - start_time) * 1000, 2)

    return {
        "status": "VALIDATED",
        "vendor_gstin": request.vendor_gstin,
        "tax_slab": "18% GST",
        "processing_latency_ms": execution_time_ms
    }

                       ┌───────────────────────────────┐
                       │     Next.js / Expo Client     │
                       └───────────────┬───────────────┘
                                       │
                                       ▼ (Sub-30ms REST / GraphQL)
                       ┌───────────────────────────────┐
                       │   Node.js Gateway / Next.js   │
                       │   (Auth, Sessions, DB CRUD)   │
                       └───────────────┬───────────────┘
                                       │
                    ┌──────────────────┴──────────────────┐
                    │                                     │
                    ▼ (Sync Job via Redis BullMQ)         ▼ (Direct Edge Query)
    ┌───────────────────────────────┐    ┌───────────────────────────────┐
    │     FastAPI Microservice      │    │     PostgreSQL (Supabase)     │
    │  • Document OCR & Parsing     │    │  • RLS Access Control         │
    │  • AI / LLM Agent Pipeline    │    │  • pgvector Semantic Search   │
    │  • Heavy PDF & Report Export  │    └───────────────────────────────┘
    └───────────────────────────────┘