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Hyeonjun Kil

Backend Engineer

kboxstar@gmail.com Seoul, South Korea github.com/kilhyeonjun

About

Backend engineer with 3 years and 7 months of experience across 4 domains (Education, Healthcare, Clinical Trials, Gaming), achieving quantifiable results including 82% BigQuery cost reduction, complete resolution of clinical trial system Deadlocks, and contributing to major hospital contract acquisitions. Specialized in system design from monolithic to Event-Driven cloud-native architectures, creating long-term business value through root cause analysis and systematic solutions.

Experience

DEV Team Server Developer 2025-01 — Present

GameDuo

Mobile game development and publishing company

  • 82% BigQuery Cost Reduction: Storage Read API adoption ($6.25→$1.1 per TB)
  • Serverless Architecture: Event-Driven Architecture based AWS Lambda migration
  • Marketing Integration Platform: Google Ads/Meta/TikTok unified dashboard
  • Game Data Audit System: Repository abstraction-based balance change tracking
Dev2 Team Docs Squad Backend Engineer 2023-06 — 2024-08

JNPMedi

Clinical trial data management solution startup with 16B KRW cumulative investment

  • Complete Deadlock Resolution: Foreign key lock timing analysis preventing clinical trial notification failures
  • New Contract Contribution: User-organization 1:N structure enabling major hospital and pharma company contracts
  • Rapid MVP Launch: VDR 3 weeks, TMF 3 months emergency deployment meeting deadlines
  • Event-Driven Architecture: AWS SNS/SQS based system reliability improvement
Dev Team Backend Engineer 2022-04 — 2023-06

Medgo

Telemedicine and medication delivery platform startup with 300K cumulative downloads

  • Architecture Modernization: Express.js → NestJS transition for code consistency and type safety
  • Unified Authentication System: JWT-based subdomain session conflict resolution
  • Medical Service Automation: OCR + public API for automated prescription medication guidance
  • Real-time Optimization: Socket.IO Room targeting for network traffic optimization
Dev Team Backend Engineer 2021-07 — 2022-04

SimpleHAN

Custom software solutions SI company

  • Bulk Data Processing: Apache POI-based batch processing for hundreds of member records
  • Multi-country Unified Auth: JWT-based cross-domain login system
  • Deployment Automation: Travis CI-based CI/CD eliminating hosting costs
  • Legacy Integration: iframe-based PHP system non-disruptive feature extension

Technical Skills

Languages

JavaScript
TypeScript
Java

Frameworks

NestJS
Express.js
Spring Boot

Databases

MySQL
Redis

AWS

Lambda
SQS
SNS
EventBridge
RDS
S3
RDS Proxy
ElastiCache

Infrastructure

AWS CDK
Serverless Framework

Monitoring

CloudWatch
DataDog
Grafana

Education

Inha Technical College

Bachelor's • Computer Information Engineering

2022-02 — 2023-02 | GPA: 4.10/4.5

Inha Technical College

Associate • Computer Information

2017-02 — 2022-02 | GPA: 4.16/4.5

Certifications

Engineer Information Processing

Human Resources Development Service of Korea • 2023-06