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Building idempotent payment rails
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Building idempotent payment rails
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  • Independent Engineer
  • Kaplan, LA
  • 04:37 (UTC -05:00)

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MohdAzfara/README.md

Hi, I'm Mohd Azfara 👋

Fintech & Distributed Systems Engineer specializing in fault-tolerant payment orchestration, multi-PSP failover routing, and high-throughput asynchronous workers.

I design and maintain backend financial infrastructure where idempotency, strict auditability, and zero-data-loss recovery are non-negotiable.

🏛️ Core Engineering Focus

  • Payment Orchestration & Routing: Multi-PSP failover mechanisms, circuit breakers, idempotency enforcement, and client-side tokenization SDKs.
  • Ledger & Reconciliation Systems: Immutable double-entry bookkeeping, automated settlement matching, balance invariants, and discrepancy alerting.
  • Asynchronous Event Pipelines: Distributed background workers utilizing Redis Streams & message queues for webhook ingestion, fraud scoring, and automated refunds.
  • Security & Compliance: PCI-DSS scope reduction, HMAC webhook verification, rate-limiting, and cryptographic payload signing.

🛠️ Technical Stack & Tooling

Domain Technologies & Standards
Languages TypeScript, Node.js, Go, SQL
Data & State PostgreSQL (ACID / Serializable Locking), Redis (Streams & Redlock)
Messaging Apache Kafka, RabbitMQ, BullMQ
Infrastructure Docker, Kubernetes, AWS (ECS, KMS, SQS), GitHub Actions
Standards RESTful APIs, gRPC, OpenAPI 3.1, ISO 20022 Concepts, Webhook Signatures

📌 Featured Open-Source Architecture

Project Architecture Role Core Stack
checkout-flow-sdk Client-side checkout & tokenization SDK with multi-provider failover TypeScript Tsup WebCrypto
payout-gateway-service High-throughput vendor payout engine & balance reconciliation API TypeScript Node.js PostgreSQL
automated-refund-worker Event-driven worker for idempotent refund pipelines & fraud audits TypeScript Node.js Redis BullMQ
double-entry-ledger-core Production-grade immutable double-entry accounting ledger enforcing strict ACID invariants TypeScript Node.js PostgreSQL

📐 Architectural Design Principles

  1. Idempotency by Default: Every state-mutating request requires an Idempotency-Key enforced at both the API boundary and database constraint layer.
  2. Event-Driven Decoupling: Critical payment paths respond synchronously only for authorization and tokenization; settlement, notifications, and audit logs are processed asynchronously via durable queues.
  3. Graceful Degradation: External gateway timeouts trigger automatic circuit breakers and multi-PSP fallback routing rather than cascading system failures.

📬 Contact & Security Disclosures

Pinned Loading

  1. checkout-flow-sdk checkout-flow-sdk Public

    ⁠Lightweight client-side checkout and payment flow SDK with multi-provider fallback and tokenization.⁠

    TypeScript 1

  2. payout-gateway-service payout-gateway-service Public

    High-throughput microservice handling asynchronous vendor payouts, reconciliation, and balance tracking.

    TypeScript 1

  3. automated-refund-worker automated-refund-worker Public

    Asynchronous background job worker for handling secure e-commerce refund pipelines and fraud audits.⁠

    TypeScript 2

  4. double-entry-ledger-core double-entry-ledger-core Public

    Production-grade immutable double-entry accounting ledger enforcing strict ACID balance invariants and audit trails.

    TypeScript 2