Flipkart Marketplace Platform  ·  View 14 of 25  ·  5 · Runtime

Checkout and Payment Sequence

The one flow that must never take money without creating an order, or create an order without taking money.

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Shopper Customer BFF Checkout Inventory Payment orch UPI / PSP Order Kafka 1. POST /checkout 2. create intent + idem key 3. reserve(listing, qty, ttl 900s) 4. Lua CAS on Redis counter 5. reservation_id 6. authorise(amount, idem key) 7. collect request 8. approve in bank app 9. webhook: authorised 10. dedupe on psp_ref 11. create order (Temporal saga) 12. confirm(reservation_id) 13. OrderCreated 14. order_id, ETA 15. confirmation screen 16. no webhook in 90 s 17. status poll, then void 18. release(reservation_id) Critical Flow — Reserve, Pay, Confirm Stock is reserved before money is asked for, and the reservation expires on its own. Every step carries the same idempotency key, so a retried webhook cannot create a second order or a second debit. v 1.0 · owner Commerce Engineering · date 2026-09

Decisions

  • Stock is reserved before payment is requested, with a 900-second TTL that expires on its own
  • One idempotency key travels from checkout intent through authorisation, webhook and order creation
  • Order creation is a Temporal saga: if confirmation fails after capture, the compensation is a refund, not a retry loop

Failure handling

  • No webhook within 90 seconds triggers a status poll, then a void — the platform never waits indefinitely on a rail
  • A duplicate webhook is deduplicated on the PSP reference before it reaches the order service
  • Every abandoned path releases the reservation explicitly; expiry is the backstop, not the mechanism

Targets

  • Checkout p95 500 ms excluding the time the customer spends in their bank app
  • Reservation call p99 under 20 ms — it is a Redis compare-and-set, not a database transaction
  • Zero tolerance on oversell and on double capture; both are alerted, not sampled
◀  Core Data Model All views Inventory Reservation Lifecycle  ▶
Solution Architecture v1.0 · Open source on Microsoft Azure · Enterprise Architecture · 2026-0914-checkout-and-payment-sequence