Hyeonjun Kil

Mobile game development and publishing company. Shared backend platform design for 12 live services, data pipeline engineering, and common package system operations

• Marketing data query cost surge (full-scan billing model) — Evaluated partitioning but rejected due to Write IOPS increase; adopted gRPC distributed reads (Storage Read API), Cut costs 82% ($6.25→$1.1 per TB)
• Batch processing collection limits (60 days) — Migrated to serverless architecture (SQS+Lambda+EventBridge), Expanded metrics range 6x (60→360 days), processing time 2h→5min
• Code duplication and convention inconsistency across 7 projects — Established shared package system (NestJS utility 10 modules + Game Server Kit 2 packages), Automated upgrades cutting deployment time 3hrs→15min
• Marketing query latency (18s) from fragmented ad platform data (Google Ads/Meta/TikTok) — Table normalization and index tuning, Performance improved 97% (18s→0.5s)
• Regulatory risk from game probability disclosure requirements — Integrated DynamicModule-based probability package across multi-game projects + CDK-based audit log pipeline, Achieved 94%+ integration test coverage (12 suites, 115 tests)

Projects: Marketing Integrated Platform, AWS Lambda Migration & Event-Driven Architecture, Internal Common Library System

Clinical trial data management solution startup with KRW 16B cumulative investment (MSA-based)

• 5+ monthly e-signature processing failures (clinical trial Deadlock) — Reproduced and identified FK shared lock deadlock pattern, Failures reduced to 0, Deadlock root cause eliminated
• VDR project schedule delay under MVP launch pressure — 3-week emergency sprint (2 BE + 1 FE), Event-Driven PDF conversion + permission-based workflow, MVP launched on schedule
• Delayed email failure detection (hours) — Constructed SES+SNS event pipeline, Bounce/complaint detection cut to seconds, Slack instant alerting (published tech blog)

Projects: Maven Docs System Reliability Improvement, Maven VDR MVP Development

Telemedicine and medication delivery platform startup with 300K cumulative downloads

• Express.js single-file (app.js) 10,000-line legacy maintainability limits — 3-stage progressive migration (single-file→layered→NestJS) + JS→TS, TDD 80% coverage, zero incidents during major releases
• Manual prescription entry bottleneck (3-5min per case) — Naver Clova OCR + MFDS (Korea FDA) API integration for full workflow automation, Pharmacist processing time cut 90% (3-5min→30sec)
• Status reflection delay in consultation/dispensing/delivery (tens of seconds) — Socket.IO real-time sync + Web Push notifications, Reduced to under 1 second, eliminated patient wait complaints

Projects: Doctor/Pharmacist Web Service Enhancement, Backend Architecture Migration

Custom software consulting firm

• Manual learning management (attendance, completion, progress tracking) — Built LMS full-stack (QR attendance, PDF certificates, Excel bulk registration), Digitized operations for 300+ students per semester
• Legacy PHP system extensibility limits — Embedded Spring Boot app via iframe + weighted-average matching algorithm, JOB Agent service launched

Projects: Learning Management System (LMS) Development