Hyeonjun Kil - Resume

Professional Summary

Backend engineer designing and operating a shared backend platform across 6 live game environments (12 branches), and leading the newly formed Platform Part to build team-wide AI development infrastructure. At GameDuo, drove an 82% BigQuery cost reduction, a 270x throughput expansion via serverless migration, and a WAL-sharded real-time game chat server (6,000 CCU target); presented the case study at Games on AWS 2025. Over 4 years and 8 months across four domains (Education, Healthcare, Clinical Trials, Gaming), consistently delivered 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. Right after the new Part launched, I designed and shipped a team-wide shared AI development context infrastructure (git-repo-based) that converts individual learnings into reusable team assets.

Core Competencies

DB Optimization, Concurrency & Distributed Systems

•Query tuning, index design, and table normalization delivering 97% performance gain
•Deadlock root cause analysis and distributed locking — diagnosing and resolving data-layer bottlenecks
•Sharded a Redis Streams WAL across a 4-shard cluster for real-time chat message ordering and horizontal scaling (accept rate 99.39→99.99%, ack p95 767ms→6.6ms)

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 2025.01 — Present

GameDuo [Detail]

Mobile game development and publishing company. Shared backend platform design for 6 live game environments (12 branches), 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
•Significant variance in AI agent productivity across team — context and learnings discovered by individuals did not propagate, causing repeated trial-and-error — Chose Git-based config-as-code over individual documentation — docs must be re-read by humans, but codified config integrates directly into the AI runtime and applies automatically. Built a team-wide AI development context platform unifying principles, coding standards, domain knowledge, agents, and hooks in one git repo, Established team-wide standardized AI context via git pull — converted individual learnings into team assets and eliminated AI productivity gap (397 domain knowledge files accumulated within ~2 weeks)

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: Real-Time Game Chat Server (Multi-Tenant), Marketing Integrated Platform, Internal Common Library System

Dev2 Team Docs Squad Backend Engineer 2023.06 — 2024.08

JNPMedi [Detail]

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

Dev Team Backend Engineer 2022.04 — 2023.06

Medgo [Detail]

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

Dev Team Backend Engineer 2021.07 — 2022.03

SimpleHAN [Detail]

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

Platform / Tooling Engineering 2026.04 — Present

Personal Projects (Side) [Detail]

Self-directed platform/tooling engineering beyond day-job scope — an AI coding workflow automation framework and side projects

Projects: Personal AI Coding Harness Framework

Presentations & Writing

Boosting Developer Productivity with Amazon Q Developer [Review]

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

Open Source

oh-my-openagent [GitHub]

• Fix cached model context limits for Anthropic providers #2664 — 2026-03

opencode [GitHub]

• Fix macOS sidecar process hang on desktop app #15136 — 2026-02

CodexBar [GitHub]

• Support kiro-cli 1.24+ Q Developer format #288 — 2026-02

Technical Skills

Backend: Node.js, TypeScript, JavaScript, NestJS, Express.js, TypeORM, Java, Spring Boot, Jest, TDD, REST API, gRPC, Testcontainers, Integration Test, OAuth2

Database: MySQL, BigQuery, ElastiCache (Redis), Redis, Redis Streams, Valkey, ClickHouse

Cloud & Infra: AWS (Lambda, ECS/Fargate, S3, SQS/SNS, CDK, EventBridge, Kinesis, Athena), GCP (BigQuery, Pub/Sub), Docker, GitHub Actions, CI/CD, Terraform, ARM64 (Graviton)

Development Productivity: Claude Code, Amazon Q Developer, Cursor, Context Engineering, Multi-Agent Orchestration, AGENTS.md

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

Training Programs

Hanghae Plus Backend 6th [GitHub] 2024.09 ~ 2024.11

Hanghae99 · [Review]

TDD and Clean Architecture, Concurrency Control, Redis

Week 1 Hall of Fame, Black Badge Completion

Professional Development

System Design Interview Study [GitHub] — System Design Interview: An Insider's Guide Vol. 1 & 2

2025.08 ~ 2026.04

Node.js Design Patterns Bible Study [GitHub] — Node core concepts, concurrency, event loop, module system

2025.10 ~ 2025.12