Ted RyuJaeyeong You

• Designing the backend that decomposes a US insurance carrier's back-office workflows into LLM agents. Each step carries domain guardrails, human-in-the-loop checkpoints, and audit logs so automation and regulatory fit advance together. Across 50 pilot cases, average handling time dropped from 20 min to 4 min (~80% reduction) (metric: pilot processing-time dashboard).
• Every agent call — input, output, intermediate state, cost, latency — is persisted as a structured event traced through OpenTelemetry, so failures can be audited, reproduced, and rolled back to satisfy compliance review.

Node.js · TypeScript · AI Agents · LangChain · AWS · PostgreSQL

• Designed an end-to-end CCTV (RTSP) → on-site GPU inference → Cloudflare R2 pipeline. Local buffering (up to 24h) plus replay uploads hold upload success at 99.7% on network recovery (metric: Cloudflare Analytics, 7-day avg).
• Presigned-URL upload API + callback flow scaled to 8 camera nodes with 0 backend deploys per addition; nodes extend horizontally with secret-based auth alone (metric: internal deploy log).

Node.js · AWS · Cloudflare R2 · RTSP · AI/Vision

• Shipped the Randibot backend MVP — RCMS / K-Startup scraping ETL + multi-tenant (tenancyId = workspaceId) architecture so onboarding a new agency is a config change. Onboarded 5 workspaces with zero code changes and sustained ~1,200 ETL runs per month (metric: per-agency config management log).

NestJS · PostgreSQL · Multi-tenancy · ETL

• (Woo-Yeon-Hee) Modeled the matching, checkout, and auto-settlement flow as a state machine with event sourcing; landed in production in 8 weeks and logged 2,500 check-ins in the first two weeks with zero critical-path defects at launch (metric: Sentry).
• (Linker) Combined Toss PG and Kakao AlimTalk via an outbox pattern with retry and DLQ handling; across ~250 weekly matches, payment failure stays near 1% (metric: PG webhook logs, 30-day avg).
• (Momentir) Designed an LLM pipeline that summarizes client notes and extracts follow-up schedules. Structured outputs flow through an agent-approval UI so nothing slips past CRM; pilot agents (n=12) reported ~30% less daily ops effort (method: user interviews).
• (Hidden Gem) Built a PostGIS + Redis location / category feed backend; index and cache strategy keep the main feed p95 under 180 ms (metric: APM p95, 7-day avg).

Node.js · NestJS · Next.js · PostgreSQL · Toss PG · LLM

• Designed and operated a B2B trading performance reporting system. Separate reporting ledger + daily/monthly snapshot batches + checksum-verified PDF pipeline sustain 99.9% batch success across 15 institutional clients (metric: CloudWatch batch logs, 30-day avg).
• Built a crypto arbitrage / market-making engine on Electron + Node.js + PostgreSQL + Redis + WebSocket. Separating the intake, strategy, and order event loops cut p95 strategy-execution latency from 120 ms to 45 ms (~63%); averages 3,000 daily fills (metric: internal latency log).

Node.js · Electron · PostgreSQL · Redis · WebSocket

• Built an AWS Cognito authentication system. A Cognito Lambda Trigger migrated 120K legacy users transparently on first login while OTP flows were introduced to the CX CRM; auth failure stays below 0.5% (metric: CloudWatch).

AWS Cognito · Node.js

• Backend Tech Lead — led a 6-person full-stack engineering team and mentored 2 junior engineers while re-cutting the NestJS backend, Vue 3 frontend, and AWS infra along coherent domain boundaries. Drove sprint-velocity and deploy-frequency improvements alongside code-review culture (metric: Jira cycle time, GitOps history).
• Built a zero-downtime blue-green pipeline on EKS with Karpenter, ArgoCD, and Helm. Deploy cadence moved from weekly to 3×/day with 500+ zero-downtime deploys over two years — 0s deploy downtime and rollbacks under 30s (metric: ArgoCD rollout logs, full audit).
• Designed a Lambda@Edge + CloudFront image CDN. On-the-fly resize + regional caching cut image p95 from 420 ms to 120 ms (~71%) while serving ~500K images/day (metric: CloudWatch RUM, 7-day avg).
• Delivered an end-to-end Blockchain DApp in ethers.js — MetaMask login, tx signing, token balance lookups. A wallet-abstraction layer and a dedicated event indexer dropped wallet-connection failure from 8% to 0.5% and stabilized on-chain sync lag (metric: frontend error log, indexer lag).
• Built a crypto derivatives exchange on OKX Broker API — separating the WebSocket market stream, REST order API, and Redis-backed position snapshots held execution latency at ~80 ms (API RTT) across 120+ supported pairs (metric: internal latency log). Engagement continued with the same CEO/CTO team as a Rootstone freelance contract.

Node.js · NestJS · TypeScript · AWS · Kubernetes · Vue 3 · SvelteKit · web3.js · Ethers.js · OKX Broker API

• Operated a Vanilla PHP 7 business-messaging dispatch API and server — 5M daily messages at a 3,000 RPS peak. Per-customer queues + weighted round-robin improved peak-hour fairness; retries use exponential backoff on isolated queues to spread load (metric: internal dispatch dashboard).
• Turned Kakao AlimTalk / FriendTalk into reusable APIs. A shared template and approval-status dashboard reduced integration effort for downstream vendors and cut CX back-office workload.

PHP 7 · Node.js · MySQL · CodeIgniter

• Built a P2P lending solution as a WordPress plugin, integrated with the Paygate Seyfert fintech API (virtual accounts, investing, repayment, status). Transaction isolation and idempotent response storage processed ~120K cumulative transactions over 2 years with 0 financial-consistency incidents (metric: daily reconciliation batch).

PHP · Wordpress · MySQL · Paygate API

• Shipped product promo-page interactions with prefers-reduced-motion handling, paired with a KWAH accessibility checklist. Dwell-time and scroll-depth KPIs hit targets alongside accessibility compliance.

JavaScript · jQuery · HTML5 · CSS3

• Delivered public-sector websites with WCAG accessibility and responsive markup. Semantic HTML, ARIA design, and a shift-left accessibility checklist carried 14 government/municipal projects through K-WCAG certification.

JavaScript · jQuery · HTML5 · CSS3 · SCSS · PHP