Hyeonjun Kil

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

GameDuo — DEV Team Platform Part Leader

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

DEV Team Platform Part Leader (2026.04 - Present)

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.

DEV Team Server Developer (2025.01 - 2026.03)

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

JNPMedi — Dev2 Team Docs Squad Backend Engineer

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

Medgo — Dev Team Backend Engineer

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

SimpleHAN — Dev Team Backend Engineer

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

TECHNICAL SKILLS

Backend: Node.js, TypeScript, JavaScript, NestJS, Express.js, TypeORM, Java, Spring Boot, Jest, TDD, REST API, gRPC, Testcontainers — Legacy-to-NestJS progressive migration, shared package system establishment, TDD-driven development, REST API / gRPC design

Database: MySQL, BigQuery, ElastiCache (Redis), Redis — Query optimization, deadlock root cause analysis, large-scale table normalization, Redis distributed locking

Cloud & Infra: AWS (Lambda, S3, SQS/SNS, CDK, EventBridge, Kinesis, Athena), GCP (BigQuery, Pub/Sub), Docker, GitHub Actions, CI/CD — Batch-to-serverless migration, EventBridge/Kinesis event pipeline design, BigQuery cost optimization, CDK-based infrastructure as code, CI/CD pipeline

Development Productivity: Claude Code, Amazon Q Developer, Cursor, Context Engineering, Multi-Agent Orchestration, AGENTS.md — AI agent-augmented development, AGENTS.md-based context engineering, multi-agent orchestration, automated code quality

PROFESSIONAL SUMMARY

CORE COMPETENCIES

EXPERIENCE

GameDuo — DEV Team Platform Part Leader

JNPMedi — Dev2 Team Docs Squad Backend Engineer

Medgo — Dev Team Backend Engineer

SimpleHAN — Dev Team Backend Engineer

TECHNICAL SKILLS

EDUCATION

Inha Technical College

Inha Technical College

CERTIFICATIONS

PRESENTATIONS & WRITING

Boosting Developer Productivity with Amazon Q Developer

Email Delivery Monitoring through AWS SES Event Logs

TRAINING PROGRAMS

Hanghae Plus Backend 6th

OPEN SOURCE

oh-my-openagent: Fix cached model context limits for Anthropic providers

opencode: Fix macOS sidecar process hang on desktop app

CodexBar: Support kiro-cli 1.24+ Q Developer format

PROFESSIONAL DEVELOPMENT

System Design Interview Study

Node.js Design Patterns Bible Study