Bui Minh Toan

E-commerce platform distributed inside 20+ banking applications.

• Built core-business APIs for an e-commerce platform distributed inside 20+ banking applications, working in a microservices codebase with Spring Boot and Spring Data JPA.
• Implemented order and payment flows against strict data-consistency requirements, using JPA transaction boundaries and Hibernate entity mapping.
• Researched and implemented XSS protection across the service layer, hardening endpoints exposed to third-party banking clients.

Two completed contracts for international clients on Upwork.

• Backend Dev & Marketplace Optimization: backend development and marketplace optimization over 154 hours (Jun – Sep 2025).
• Open Source Modification & Software MVP: modified an open-source codebase into a software MVP on a fixed-price contract, rated 5.0/5 by the client (Apr – Jul 2025).

Two simulated banking systems built to work directly on transaction integrity, concurrency control and distributed-transaction failure handling.

• Double-entry core ledger: append-only, immutable ledger enforcing Debit = Credit on every transaction; race conditions on hot accounts controlled with pessimistic locking and fixed-order lock acquisition.
• Interbank payment gateway: parses and validates ISO 20022 messages (pain.001, pacs.008) and settles end-of-day with chunk-oriented Spring Batch.
• Distributed transactions: Saga orchestration chosen over 2PC, with idempotency keys on internal REST calls, compensating transactions on step failure, and retry / dead-letter handling for exception flows.
• Each design decision recorded as an ADR (problem, options, rationale, trade-offs), with a public roadmap and devlog documenting build progress.