API (FastAPI)
  ├── Orders / Products / Webhooks / Metrics
  ├── Services: checkout, cancellation, refund, orders
  ├── Domain: order state machine (Created → Processing → Paid / Cancelled / Refunded)
  └── RabbitMQ: Outbox pattern, event idempotency

Workers:
  ├── outbox_publisher      — publish order.paid / cancelled / refunded
  ├── order_events_consumer — process events from RabbitMQ
  └── order_cancellator     — cancel stale Created orders

E-Commerce Backend

The project is an e-commerce backend that handles order payments with Stripe, domain events via the transactional outbox, and runs API and background workers in Docker Compose.

The project was built with a focus on production-style patterns: fixed order state transitions via a state machine, idempotent checkout, event-idempotent RabbitMQ consumer, webhook-driven updates, observability through metrics, and logging infrastructure.

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Quick start

cp .env.example .env
docker compose up --build

On the first run, Compose will automatically:

1. Apply database migrations
2. Seed sample products
3. Start the API, workers, and observability stack

When logs settle, open http://localhost:8000/docs — the API is ready to use.
No Stripe account is required: .env.example uses PAYMENTS_PROVIDER=mock.

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What it does

• POST /orders Create orders
• POST /orders/{id}/checkout Checkout via Stripe PaymentIntent (confirm=true in the current integration)
• POST /orders/{id}/cancel Cancel orders in Created (through API or timeout worker)
• POST /orders/{id}/refund Refund paid orders via Stripe refund
• Emit domain events (order.paid, order.cancelled, order.refunded) to RabbitMQ after the database commit

Payment and refund final state is applied from Stripe webhooks (signature verification, idempotent handling). The API and workers update PostgreSQL; side effects are written to an outbox table and published asynchronously.

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Stack

• Python 3.12, FastAPI, asyncio
• PostgreSQL 16, Alembic migrations, SQLAlchemy 2 (async)
• Redis
• RabbitMQ
• Stripe API + webhooks
• Prometheus, Grafana
• Docker Compose

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Run the full stack

Service	URL
API	http://localhost:8000
API docs	http://localhost:8000/docs
Grafana	http://localhost:3000 (admin / admin)
Prometheus	http://localhost:9090
RabbitMQ UI	http://localhost:15672 (guest / guest)

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Background workers

Worker	Module	Purpose
outbox_publisher	app.workers.outbox_publisher	Polls outbox, publishes to order.events, marks published_at
order_events_consumer	app.workers.order_events_consumer	Consumes order.paid / order.cancelled / order.refunded (logs; hook for digital fulfillment)
order_cancellator	app.workers.order_cancellator	run_batch() selects stale Created orders and calls CancellationService

Cancellation timeout for order_cancellator service is configured in the worker as STALE_ORDER_AFTER (default 10 seconds in code).