Hyeonjun Kil
Backend Engineer
Professional Summary
Backend engineer who finds and eliminates structural bottlenecks. At GameDuo, building a shared backend platform for 12 live services while cutting BigQuery costs by 82%, expanding pipeline throughput 270x via serverless migration, and presenting the case study at Games on AWS 2025. Over 4 years and 6 months across four domains (Education, Healthcare, Clinical Trials, Gaming), consistently delivering DB optimization, concurrency control, and event-driven architecture design. Since late 2024, I have applied this same structural thinking to the development process itself — orchestrating multiple AI agents by role to design and ship production software.
Core Competencies
DB Optimization & Concurrency Control
- Query tuning, index design, and table normalization delivering 97% performance gain
- Deadlock root cause analysis and distributed locking — diagnosing and resolving data-layer bottlenecks
Serverless Architecture & Cost Optimization
- Batch-to-EDA migration expanding throughput 270x, Lambda hybrid pipeline design
- BigQuery pricing model analysis with read-method switch — 82% cost reduction
Legacy Modernization & Reliability
- Express monolith to NestJS via 3-stage progressive migration, TDD-driven incident-free deployments during major releases
- Shared package system unifying 7 projects, cutting deployment from 3h to 15min
AI-Augmented Development Productivity
- Integrated Claude Code, Amazon Q, and other AI agents into development workflows, driving team-wide adoption (Games on AWS 2025 speaker)
- Established team-wide TDD foundation to ensure AI-generated code reliability — built a quality governance layer for AI-assisted development
Experience
DEV Team Platform Part Leader
GameDuo
2025.01 — Present
Mobile game development and publishing company. Shared backend platform design for 12 live services, data pipeline engineering, and common package system operations
- Newly formed platform team lacked task tracking and sizing framework — Designed 7-stage workflow (BACKLOG→SIZE REVIEW→DONE), handling rules for 4 task types, transition validators, and ticket template library, Standard operating framework deployed immediately upon team formation — task-type handling rules and decision criteria established simultaneously
- Existing sizing criteria did not reflect AI-assisted development time reduction with Claude Code — Established 5-dimension scoring framework and per-domain Claude Code time-discount rules (test writing ~80%, pattern replication ~70%), Team-consensus AI time-discount rules established, ensuring equitable performance measurement before and after Claude Code adoption
- 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 from batch processing to EDA-based on-demand pipeline — distributing peak load and enabling throughput scaling, Expanded metrics range 6x (60→360 days), processing time 2h→5min
- Code duplication and convention inconsistency across 7 projects — Replaced manual code sync with shared NestJS package system (10 utility modules + Game Server Kit, auto-deploy), Automated upgrades cutting deployment time 3hrs→15min
- Marketing query latency (18s) from fragmented ad platform data (Google Ads/Meta/TikTok) — Normalized read path + index tuning to avoid full-scan on 100-column table, 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, In-Game Multi-Language Translation System
View DetailsDev2 Team Docs Squad Backend Engineer
JNPMedi
2023.06 — 2024.08
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
View DetailsDev Team Backend Engineer
Medgo
2022.04 — 2023.05
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
View DetailsDev Team Backend Engineer
SimpleHAN
2021.07 — 2022.03
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
View DetailsPresentations & Writing
Email Delivery Monitoring through AWS SES Event Logs
Internal Seminar → Tech Blog — 2024-03
Presented internally then published as tech blog
Open Source
Technical Skills
Education
Inha Technical College
Bachelor's (Advanced Major Program, Concurrent Employment) • Computer Information Engineering
2022.02 — 2023.02 GPA: 4.10/4.5
Inha Technical College
Associate (Concurrent Employment) • Computer Information
2017.02 — 2022.02 GPA: 4.16/4.5
Certifications
SQLD (Structured Query Language Developer)
Korea Data Agency • 2025-12
Engineer Information Processing
Human Resources Development Service of Korea • 2023-06