Kasa.
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Kasa

Backend Software Engineer

homieyang@outlook.com blog.ezlo.me Taiwan
Project Experience · Selected Work

EZLO — Bitfinex Auto-Lending Platform (Personal Side Project)

Personal Project Live product ↗

Independently designed, built, and operated an automated Bitfinex funding-lending platform with a market depth-anchored dynamic pricing strategy, idempotent order placement, circuit breaking, and full audit/observability — owning everything from architecture to production operations. Started as a Python/FastAPI + Vue prototype, later rewritten end-to-end in Spring Boot + Next.js for stability and maintainability.

Key Responsibilities

  • Sole full-stack owner: backend, frontend, database, deployment, and production operations
  • Designed the market depth-anchored dynamic lending pricing strategy and order engine
  • Built reliability and security mechanisms: key encryption, audit logging, notifications, and monitoring
  • Set up containerized deployment and CI/CD to keep the service running automatically and reliably

Technical Implementation

  • Backend in Spring Boot 3 / Java 21 — RESTful API with Spring Security JWT and TOTP two-factor auth
  • Frontend in Next.js / React + Tailwind CSS + shadcn/ui, statically exported and deployed on Cloudflare Pages
  • Lending engine runs on a scheduled cycle with periodic reconciliation, using a write-DB-before-order idempotent design to avoid duplicate placements
  • Depth-anchored dynamic pricing against the funding order book, guarded by rate sanity checks
  • Integrated Bitfinex REST v2 (HMAC-SHA384) protected by a Resilience4j circuit breaker and a Redis token-bucket rate limiter
  • PostgreSQL (Flyway-versioned) + Redis (cache / distributed lock / rate limiting); user API keys stored AES-256 encrypted
  • Email (Resend) and Telegram notifications for earnings digests and system alerts
  • Tamper-evident audit log via a hash chain; monitoring and alerting with Prometheus + Grafana + Alertmanager
  • Multi-stage Docker builds + Cloudflare Tunnel reverse proxy; GitHub Actions CI/CD with secrets managed in 1Password

Results & Impact

  • Engine runs fully automated; idempotency and reconciliation guarantee no duplicate orders and self-healing back to a consistent state on failures
  • Circuit breaking and rate limiting isolate exchange-side outages, markedly improving resilience
  • Structured logging with Prometheus/Grafana monitoring makes issues fast to pinpoint
  • Evolved from a single-person script into a layered, testable, maintainable multi-module platform

Yu Xiang Software Technology Co., Ltd.

2023/10 - Present

Joined the technical team focusing on third-party payment gateway integration, gaming platform integration, and backend system optimization to ensure product operations and payment stability.

Key Responsibilities

  • Developed and integrated third-party payment gateway APIs using Java SpringBoot
  • Integrated gaming merchant platforms, optimizing API efficiency and data synchronization
  • Optimized backend management systems to improve operational efficiency and stability

Technical Implementation

  • Designed and integrated multiple third-party payment APIs achieving 99.9% payment success rate
  • Optimized backend system response speed, reducing average request processing time by 30%
  • Provided cross-departmental technical support, rapidly resolving issues and optimizing workflows

Results & Impact

  • Enhanced payment stability and improved user payment experience
  • Reduced payment and gaming interface issue reports by 50%
  • Effective team collaboration, improved backend system maintenance efficiency and scalability

Data Express Digital Technology

2022/09 - 2023/10

Served as C# Engineer responsible for developing POS systems, backend management systems, and BI reports while ensuring system stability and continuous optimization.

Key Responsibilities

  • Developed POS systems using C# and integrated various peripheral devices
  • Built backend systems using .NET Core supporting scheduled tasks and data management
  • Developed BI reports providing data visualization and decision support
  • Maintained and optimized existing systems, rapidly resolving user issues

Technical Implementation

  • Established scheduled task modules improving automated data processing efficiency
  • Integrated with BI tools, created 20+ report types providing business decision insights
  • Collaborated with team, maintained existing systems with stable operation for 12+ months

Results & Impact

  • Improved report query speed by 40%, enhanced data-driven decision support
  • Reduced POS system issue reports by 30%
  • Promoted cross-departmental collaboration, significantly improved overall development efficiency