Add Dev.to blog post: License expiration tracker writeup

docs/blog/license-tracker-fastapi.md

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+---
+title: "I Built a License Expiration Tracker That Emails You Before Things Expire — FastAPI + Stripe + Docker"
+published: false
+description: "LicenseLoop tracks business licenses, sends automated reminders at 30/7/1 days before expiration, and handles Pro upgrades via Stripe. Full-stack Python."
+tags: python, fastapi, saas, docker
+cover_image: ""
+canonical_url:
+---
+
+Nobody thinks about business licenses until they expire. Then it's a scramble — fees, penalties, sometimes suspended operations. I built **LicenseLoop** to solve a boring but real problem: track expiration dates and automatically email reminders before things go bad.
+
+It's not glamorous. It's not AI. But it's the kind of tool that actual businesses would pay for, and building it taught me more about production Python than any tutorial.
+
+---
+
+## What it does
+
+1. You create an account (JWT-based auth with bcrypt)
+2. You add your licenses — business license, health permit, fire inspection, whatever
+3. LicenseLoop shows a dashboard with color-coded expiration status
+4. Background tasks send email reminders at 30 days, 7 days, and 1 day before expiration
+5. Free tier gets 5 licenses, Pro tier ($X/mo via Stripe) gets unlimited
+
+---
+
+## Architecture
+
+```
+FastAPI + Uvicorn
+├── SQLModel + SQLite (zero-config database)
+├── Stripe Checkout + Webhooks (billing)
+├── SMTP Mailer (background task alerts)
+├── Jinja2 Templates (dashboard UI)
+└── Docker + Docker Compose (deployment)
+```
+
+### Why FastAPI?
+
+- **Async-native** — email sending and Stripe calls don't block the server
+- **Pydantic/SQLModel** — one model class serves as both the API schema and the database table
+- **Automatic docs** — OpenAPI spec generated for free at `/docs`
+- **Lifespan events** — `init_db()` runs on startup, database is ready before the first request
+
+```python
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    init_db()
+    yield
+
+app = FastAPI(title="LicenseLoop", version="1.0.0", lifespan=lifespan)
+```
+
+### Why SQLite?
+
+For a single-tenant app with a few hundred licenses, SQLite is perfect. No server to manage, no connection strings, no Docker container for the database. The file lives on disk and SQLModel handles the ORM.
+
+When (if) you need to scale, the SQLModel code transfers to PostgreSQL with a connection string change. That's the beauty of an ORM — you don't rewrite queries.
+
+---
+
+## The reminder system
+
+The background task processor checks daily for licenses approaching expiration:
+
+- **30 days out** — "heads up, this is coming"
+- **7 days out** — "you should start the renewal process"
+- **1 day out** — "this expires tomorrow"
+
+The SMTP mailer sends through whatever provider you configure — Mailtrap for dev, SendGrid for production, or any SMTP server.
+
+This is the kind of feature that separates "student project" from "could actually be a product." Anyone can build a CRUD form. The value is in the automation that runs when nobody's looking.
+
+---
+
+## Stripe integration
+
+The billing flow:
+
+1. User clicks "Upgrade to Pro"
+2. Backend creates a Stripe Checkout Session
+3. User pays via Stripe's hosted payment page
+4. Stripe sends a webhook to `/api/billing/webhook`
+5. Backend validates the webhook signature, upgrades the user's plan
+
+```python
+@router.post("/webhook")
+async def stripe_webhook(request: Request):
+    payload = await request.body()
+    sig = request.headers.get("stripe-signature")
+    event = stripe.Webhook.construct_event(payload, sig, webhook_secret)
+
+    if event.type == "checkout.session.completed":
+        # Upgrade user to Pro
+        ...
+```
+
+The webhook signature validation is critical — without it, anyone could POST fake events to your webhook endpoint and give themselves a free upgrade.
+
+---
+
+## Testing
+
+```bash
+pytest
+```
+
+The test suite covers the core license management logic — CRUD operations, expiration calculations, and authentication flows. Tests run against an in-memory SQLite instance so they're fast and isolated.
+
+---
+
+## Docker deployment
+
+```dockerfile
+FROM python:3.11-slim
+WORKDIR /app
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+COPY . .
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]
+```
+
+```bash
+docker-compose up --build
+```
+
+One command and you're running. The Docker Compose setup handles the app container and any supporting services.
+
+---
+
+## What I learned
+
+1. **Background tasks are where the value lives.** The CRUD part of this app took a day. The reminder system is what makes it useful, and it took the most thought — timing, deduplication, email templates, error handling.
+2. **Stripe webhooks are security-critical.** Always validate the signature. Always handle duplicate events (idempotency). Always log webhook processing for debugging.
+3. **SQLite is fine.** The internet wants you to use Postgres for everything. For a single-service app with predictable data patterns, SQLite removes an entire class of operational concerns.
+4. **Boring problems are good portfolio pieces.** An AI chatbot is cool but competitive. A license tracker is boring but shows you can build something a real business would use.
+
+---
+
+*Source: [github.com/SSH-PuR66/LicenseLoop](https://github.com/SSH-PuR66/LicenseLoop)*