How a Developer Built a Fraud-Resistant Wallet Engine Using Kafka and TypeScript

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A software developer has detailed the architecture behind a fintech wallet engine designed to handle credits, debits, and transfers without losing money even during system failures. The system is built on NestJS, PostgreSQL, Apache Kafka, and Redis, with each component serving a distinct role in ensuring reliability and auditability. A double-entry bookkeeping model is central to the design, ensuring every financial operation produces paired debit and credit ledger entries whose net sum must always equal zero. The Transactional Outbox pattern is used to guarantee that events are published to Kafka only after a database transaction is confirmed, preventing message loss. Redis handles idempotency checks to block duplicate requests, while running balance snapshots on each ledger entry allow full reconstruction of any wallet's history at any point in time.

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