Hyeonjun Kil

PROFESSIONAL SUMMARY

Backend engineer with 4 years and 5 months of experience across 4 domains (Education, Healthcare, Clinical Trials, Gaming), leading 20+ projects with quantifiable results: 82% BigQuery cost reduction, CDK-based analytics infrastructure as code, and internal NPM package system. Specializes in serverless/EDA-based system design and cloud cost optimization. Presented at Games on AWS 2025 on leveraging AI to scale data pipeline capacity 270x through batch-to-Lambda architecture improvement. Ensures system reliability through architecture-level root cause analysis, including resolving recurring Deadlock patterns.

CORE COMPETENCIES

Cost Optimization & Performance

Cloud cost structure analysis and pricing model optimization — 82% cost reduction ($6.25→$1.1 per TB)
Bulk data processing bottleneck diagnosis — 72% sync time reduction via bulk operation migration
Data model redesign and query optimization — 97% query performance improvement (18s→0.5s)

System Design & Architecture

Event-Driven Architecture design — batch→Lambda serverless migration reducing processing 2hrs→5min, 270x pipeline expansion
Multi-project shared package system design — code consistency and reusability across 12 projects
Legacy progressive modernization strategy — staged architecture migration + TDD adoption achieving zero-incident deployments

Reliability & Quality

Root cause analysis — reproduced and identified lock deadlock patterns in recurring failures, resolving at the architecture level
Data consistency design — outbox pattern (event integrity), distributed lock (concurrency control)
Regulatory compliance framework — integrated verification package across 12 projects + CDK-based audit log analytics pipeline achieving 94%+ coverage

Technical Sharing & Development Culture

AI development adoption leadership — guided team on AI agent workflows (Cursor, Claude Code) and context engineering practices, driving company-wide AI adoption (Games on AWS 2025 speaker)
TDD foundation for AI code reliability — established test-driven development framework to ensure AI-generated code quality, embedding TDD culture across the team
Developer meeting-driven knowledge sharing — authored shared library contribution guides and merge rules, established code conventions, standardized architecture patterns across teams

EXPERIENCE

GameDuo — DEV Team Server Developer

2025.01 - Present

Mobile game development and publishing company

Resolved escalating marketing data query costs by switching BigQuery read method, achieving 82% cost reduction ($6.25→$1.1 per TB)
Overcame batch processing limitations by migrating to serverless architecture, expanding marketing metrics collection range 6x (60→360 days)
Eliminated code duplication across multi-game projects by building NestJS utility (10 modules) + Game Server Kit (2 packages), achieving code consistency across 12 projects
Designed and implemented Git-like Audit Log + 3-Way Merge engine to automate balance data change tracking and merging across 6 games, resolving delayed incident response
Unified 3 ad platform (Google Ads/Meta/TikTok) data and improved query performance 97% (18s→0.5s) through table normalization
Addressed game probability disclosure regulation risk by integrating DynamicModule-based package across 12 projects, building CDK-based audit log pipeline (94%+ coverage)

JNPMedi — Dev2 Team Docs Squad Backend Engineer

2023.06 - 2024.08

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

Reduced 5+ monthly e-signature processing failures to zero by reproducing and identifying FK shared lock deadlock pattern, fundamentally resolving clinical trial Deadlock
Expanded user-organization 1:1 to 1:N mapping with full API backward compatibility ensuring zero-disruption migration, enabling multi-org onboarding for enterprise hospitals and pharma
Deployed as part of 3-person team (2 BE + 1 FE) for 3-week emergency sprint on delayed VDR project, implementing Event-Driven PDF conversion and permission-based workflow to meet MVP launch deadline
Resolved delayed detection of email delivery failures by building event-driven monitoring pipeline for real-time bounce/complaint tracking with instant alerting (published tech blog)

Medgo — Dev Team Backend Engineer

2022.04 - 2023.05

Telemedicine and medication delivery platform startup with 300K cumulative downloads

Modernized 3,000-line legacy codebase via 3-stage progressive migration (single-file → layered → NestJS) with JS→TS + 80% TDD coverage, maintaining zero post-deployment incidents
Resolved session conflicts across 3 subdomains on 300K-download platform by building JWT-based token authentication in 3 weeks, enabling seamless user switching
Automated full prescription-to-medication-guide workflow via Naver Clova OCR + MFDS (Korea FDA) API integration, cutting pharmacist processing time 90% (3-5min→30sec)
Introduced Socket.IO-based real-time status sync + Web Push notifications, reducing status reflection delay from tens of seconds to instant and eliminating patient wait complaints

SimpleHAN — Dev Team Backend Engineer

2021.07 - 2022.03

Custom software consulting firm

Developed LMS core features (QR attendance, PDF certificates, Excel bulk registration) full-stack over 10 months, digitizing learning management for 300+ students per semester
Overcame legacy PHP system limitations via cross-frame integration, implementing weighted matching algorithm and counselor back-office to launch JOB Agent service
Built cross-domain auth server to unify login across 5 country-specific websites into a single authentication system

TECHNICAL SKILLS

Backend: TypeScript, NestJS, Express.js, TypeORM, Java, Spring Boot, Jest — Legacy-to-NestJS progressive migration, shared package system across 12 projects, 80% TDD coverage

Database: MySQL, BigQuery, ElastiCache (Redis) — Query optimization (18s→0.5s), 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 — Batch-to-serverless migration (270x expansion), 82% BigQuery cost reduction, CDK-based analytics infrastructure as code

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

AWARDS

2014 Youth Future Imagination Technology Competition Gold Award (KIPO Commissioner's Award) — AppKeeper mobile app launch, 2014

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

Tech Blog — 2024.03

Mailing System Email Delivery Result Tracking Feature

Internal Seminar — 2024.02

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 Study Vol. 2 (2026.01 ~ Present) | Node.js Design Patterns Bible Study (2025.10 ~ 2025.12) | System Design Study Vol. 1 (2025.08 ~ 2025.10) | AWS SAA Study Group (2023.09 ~ 2023.12)

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

AWARDS

PRESENTATIONS & WRITING

Boosting Developer Productivity with Amazon Q Developer

Email Delivery Monitoring through AWS SES Event Logs

Mailing System Email Delivery Result Tracking Feature

TRAINING PROGRAMS

Hanghae Plus Backend 6th

OPEN SOURCE

kiro-gateway: Remove :ro from Docker SQLite volume mount

CodexBar: Support kiro-cli 1.24+ Q Developer format

oh-my-opencode: Integrate plugin skills into unified skill discovery

atlassian-skills: Use ADF format for comments in Jira Cloud API v3

atlassian-skills: Migrate to new Jira Cloud search API endpoint

kiro-gateway: Skip thinking tag injection when toolResults present

kiro-gateway: Reload SQLite credentials before AWS SSO OIDC token refresh

SuperClaude_Plugin: Correct marketplace name in documentation

cyan: framework "NOT IN" query condition addition

PROFESSIONAL DEVELOPMENT