FastAPI Production Deployment on DomainIndia VPS (Gunicorn + Uvicorn + nginx + PostgreSQL)

# FastAPI Production Deployment on DomainIndia VPS (Gunicorn + Uvicorn + nginx + PostgreSQL) ## Why FastAPI - Async-first (handles 10K+ concurrent connections) - Pydantic for type-safe request/response models - Auto-generated OpenAPI/Swagger docs at `/docs` - 3-5× faster than Flask, same-league as Node.js Express - Massive ecosystem (SQLAlchemy 2, Alembic, Celery, APScheduler) Good fit: REST APIs, WebSocket services, ML inference endpoints. Less ideal for server-rendered HTML apps — use Django or Flask for those. ## Stack we're deploying ``` Client → nginx (443) → Gunicorn → 4× Uvicorn workers → FastAPI app → PostgreSQL ↑ Redis (cache/queue) ``` ## Step 1 — Prepare VPS ```bash # AlmaLinux 9 sudo dnf install -y python3.12 python3.12-devel python3-pip nginx postgresql-server postgresql-contrib redis git certbot python3-certbot-nginx # Ubuntu 22.04+ sudo apt install -y python3.12 python3.12-venv python3-pip nginx postgresql redis git certbot python3-certbot-nginx # Create app user sudo useradd -r -m -s /bin/bash fastapi sudo su - fastapi ``` ## Step 2 — Sample FastAPI app `~fastapi/app/main.py`: ```python from contextlib import asynccontextmanager from fastapi import FastAPI, Depends, HTTPException from fastapi.responses import JSONResponse from sqlalchemy.ext.asyncio import AsyncSession from pydantic import BaseModel, EmailStr import os from .db import get_db, engine from .models import User @asynccontextmanager async def lifespan(app: FastAPI): # Startup print("Starting up") yield # Shutdown await engine.dispose() print("Shutting down") app = FastAPI( title="MyAPI", version="1.0.0", lifespan=lifespan, ) class UserCreate(BaseModel): email: EmailStr name: str class UserOut(BaseModel): id: str email: str name: str class Config: from_attributes = True @app.get("/health") async def health(): return {"status": "ok", "version": "1.0.0"} @app.post("/users", response_model=UserOut) async def create_user(payload: UserCreate, db: AsyncSession = Depends(get_db)): user = User(email=payload.email, name=payload.name) db.add(user) await db.commit() await db.refresh(user) return user @app.get("/users/{user_id}", response_model=UserOut) async def get_user(user_id: str, db: AsyncSession = Depends(get_db)): user = await db.get(User, user_id) if not user: raise HTTPException(404, "Not found") return user ``` `~fastapi/app/db.py`: ```python from sqlalchemy.ext.asyncio import create_async_engine, AsyncSession, async_sessionmaker import os DATABASE_URL = os.getenv("DATABASE_URL") # postgresql+asyncpg://... engine = create_async_engine(DATABASE_URL, pool_size=10, max_overflow=5) SessionLocal = async_sessionmaker(engine, expire_on_commit=False) async def get_db(): async with SessionLocal() as session: yield session ``` `~fastapi/app/models.py`: ```python import uuid from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column from sqlalchemy import String class Base(DeclarativeBase): pass class User(Base): __tablename__ = "users" id: Mapped[str] = mapped_column(String, primary_key=True, default=lambda: str(uuid.uuid4())) email: Mapped[str] = mapped_column(String(255), unique=True) name: Mapped[str] = mapped_column(String(100)) ``` `~fastapi/requirements.txt`: ``` fastapi==0.114.0 uvicorn[standard]==0.30.6 gunicorn==22.0.0 sqlalchemy==2.0.35 asyncpg==0.29.0 alembic==1.13.2 pydantic[email]==2.8.2 python-dotenv==1.0.1 ``` ## Step 3 — Install + setup venv ```bash cd ~fastapi python3.12 -m venv .venv source .venv/bin/activate pip install -r requirements.txt ``` ## Step 4 — PostgreSQL ```bash # As root sudo postgresql-setup --initdb sudo systemctl enable --now postgresql sudo -u postgres psql <

Tool	Best for	Complexity
FastAPI BackgroundTasks	Short tasks triggered by request	Zero — built-in
APScheduler	Cron-like schedules in-process	Low
Celery + Redis	Heavy async work, multiple workers	Medium
Arq	Lightweight async task queue	Low

Start with `BackgroundTasks` for simple needs; scale to Celery or Arq when you need retries + multiple worker machines. ## Common pitfalls ## FAQ