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Payment Gateway Simulation System
Distributed, fault-tolerant payment infrastructure simulation with idempotent APIs
Node.jsTypeScriptPostgreSQLREST APIsWebhooksEvent-Driven ArchitectureDocker
Overview
A distributed payment infrastructure simulating the full authorization → capture → void → refund lifecycle, built to explore idempotency, fault tolerance, and transactional consistency under concurrency.
Problem
Payment systems must guarantee correctness under network retries, duplicate requests, and concurrent operations — mistakes mean double charges or lost transactions.
Solution
Idempotent APIs for every state transition, a webhook delivery engine with exponential backoff and dead-letter queues, and PostgreSQL row-level locking to guarantee ACID consistency under high concurrency.
Architecture
- 1Client/API layer exposing authorize, capture, void, and refund endpoints — each idempotent via request keys
- 2Webhook delivery engine with exponential backoff, dead-letter queues, and event replay
- 3PostgreSQL with row-level locking guaranteeing consistency during concurrent state transitions
- 4Dockerized services for local development and reproducible testing
Technical Challenges
- Preventing duplicate processing when clients retry after timeouts — solved with idempotency keys.
- Guaranteeing at-least-once webhook delivery without introducing duplicate side effects.
- Avoiding deadlocks under high-concurrency payment operations with row-level locking.
Results
- Demonstrated correct behavior for authorize/capture/void/refund lifecycles under retry and concurrency scenarios.
- Reusable webhook delivery pattern (backoff + DLQ + replay) applicable to any event-driven integration.