Distributed Systems2023 - 2024Senior Backend Architect

Real-Time FinTech Settlement Engine

Event-Driven Ledger System with Sub-10ms Transaction Validation

Daily Processing Volume

$12M+

Settled securely every 24h

Transaction Latency

9.4ms

End-to-end event resolution

Data Integrity

100%

Zero reconciliation discrepancies

Audit Accuracy

100%

Cryptographic ledger hashing

Technology Stack & Tools Used

Node.jsTypeScriptApache KafkaPostgreSQLPrismaDockerAWS ElastiCacheDatadog

Architectural Overview & System Boundaries

Built on an Event-Sourcing pattern using Apache Kafka as the append-only event log, paired with PostgreSQL isolated schemas for transactional double-entry accounting. Write models and Read models are completely decoupled via CQRS (Command Query Responsibility Segregation).

Core Engineering Challenges

1Guaranteeing exactly-once processing across unreliable payment gateway Webhooks.

2Maintaining atomic balance updates under concurrent burst payouts.

3Meeting strict PCI-DSS Compliance & immutable audit logs.

Critical Architectural Decisions & Trade-Offs

Idempotency Key Reservation via Redis Redlock

To prevent duplicate withdrawals from concurrent user taps, a distributed lock guarantees unique request key execution before database write phases.

Impact: Completely eliminated duplicate charge incidents across 4 million monthly transactions.

CQRS Read-Optimized Materialized Views

Complex account statement queries slowed down double-entry write tables. Decoupling reads into optimized PostgreSQL materialized views eliminated table locks.

Impact: Query response times dropped from 1.2s to 14ms.

### Financial Security & Systems Integrity Processing high-frequency financial settlements demands zero tolerance for data drift or race conditions. I designed a double-entry ledger framework where every credit requires an equal debit, secured by cryptographic hash chaining. ### System Flow - **Ingress Event**: Webhook payload validated with HMAC-SHA256 signature. - **Kafka Pipeline**: Event published to partitioned topic keyed by Account ID ensuring strict per-account sequence ordering. - **Ledger Worker**: Distributed worker validates balance sufficiency, applies cryptographic double-entry write, and emits transactional completion event. - **Audit Engine**: Background worker computes Merkle tree root hashes for end-of-day banking reconciliation.

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