Hyeonjun Kil

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 5 months across four domains (Education, Healthcare, Clinical Trials, Gaming), consistently delivering DB optimization, concurrency control, and event-driven architecture design. Since late 2024, integrating AI agents into the development workflow to amplify productivity.

CORE COMPETENCIES

DB Optimization & Concurrency Control

From query tuning, index design, and table normalization (97% performance gain) to deadlock root cause analysis and distributed locking — diagnosing and resolving data-layer bottlenecks

Serverless Architecture & Cost Optimization

Batch-to-EDA migration expanding throughput 270x, BigQuery pricing model analysis with read-method switch (82% cost reduction), Lambda hybrid pipeline design

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

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)

EXPERIENCE

GameDuo — DEV Team Server Developer

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

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

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 — Legacy-to-NestJS progressive migration, shared package system establishment, TDD-driven development, REST API 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, BigQuery cost optimization, CDK-based analytics infrastructure as code, CI/CD pipeline

Development Productivity: Claude Code, Amazon Q Developer, Cursor, Context Engineering — AI agent-augmented development, context engineering, automated code quality

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

PRESENTATIONS & WRITING

Boosting Developer Productivity with Amazon Q Developer

Conference Talk — 2025.10

Games on AWS 2025 Customer Session

Email Delivery Monitoring through AWS SES Event Logs

Internal Seminar → Tech Blog — 2024.03

Presented internally then published as tech blog

TRAINING PROGRAMS

Hanghae Plus Backend 6th

2024.09 ~ 2024.12

Hanghae99

TDD and Clean Architecture, Concurrency Control, Redis

Week 1 Hall of Fame, Black Badge Completion

PROFESSIONAL DEVELOPMENT

System Design Interview Study

2025.08 ~ Present

System Design Interview: An Insider's Guide Vol. 1 & 2

Node.js Design Patterns Bible Study

2025.10 ~ 2025.12

Node core concepts, concurrency, event loop, module system

PROFESSIONAL SUMMARY

CORE COMPETENCIES

EXPERIENCE

GameDuo — DEV Team Server Developer

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

kiro-gateway: Skip thinking tag injection + SSO token refresh (2 merged PRs)

atlassian-skills: ADF comment format + search endpoint migration (2 merged PRs)

cyan: Add "NOT IN" query condition to framework

PROFESSIONAL DEVELOPMENT

System Design Interview Study

Node.js Design Patterns Bible Study