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Distributed Systems Engineer · Tech Lead

Woon Fei Lai

I build distributed systems, AI-powered products and commerce platforms: from networking and identity to LLM pipelines and Shopify apps.

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Chapter 01 · Origin

About

Most of my career has gone into the parts of a system people only notice when they break: how a request finds its way across the world, what happens when a server disappears, and how a service decides who you are and what you're allowed to do.

I've led teams and designs at large scale, and I still like being close to the code. Three ideas run through everything I build.

  1. Clear designs that a new teammate can read in an afternoon
  2. Boring, reliable operations: alarms that mean something, runbooks that work
  3. Leave every system simpler than I found it

Chapter 02 · First light · Full Stack Developer

Web development

Before platforms and planet-scale networks, there were web pages: online shops, search optimisation, and the endless work of making pages load faster. It taught me the lesson I still use every day: users feel every millisecond, every layout shift, every image that arrives late.

  1. First byte: fast servers and caching
  2. Layout: structure arrives before decoration
  3. Content: the words and images people came for
  4. Interactive: ready to use, nothing blocking

Chapter 03 · Structure · Senior Software Engineer

Product platforms

I led a team building the shared foundations that many product teams stood on: a front-end framework in React, API services in Node.js, and the CI/CD pipelines on AWS that shipped them. Good platforms are invisible: teams move faster without ever thinking about what's underneath.

  1. Infrastructure as code: repeatable, reviewable environments
  2. Services and APIs with clear contracts
  3. Shared UI and tooling, so every team starts ahead
  4. Product teams ship on top, without waiting on anyone

Chapter 04 · Protection · Senior Software Engineer

Security & identity

I led the design of authentication, authorization and account-lifecycle services for enterprise customers, in Java and Spring Boot on AWS. Identity is the front door of every product: it has to be effortless for the right people and impossible for everyone else, and access has to disappear the day someone leaves.

  1. Who are you? Single sign-on
  2. Prove it: tokens, not passwords flying around
  3. A short-lived key with a narrow scope
  4. Access to exactly what you need, nothing more

Chapter 05 · A connected world · Senior Software Engineer

Distributed systems at scale

Today I lead designs for high-traffic, globally distributed services: routing every request to the nearest healthy location, caching so the far side of the world feels local, and the observability that tells you what's happening before users do. I also mentor engineers and review designs across teams.

  1. A request leaves a phone
  2. It lands at the nearest edge location
  3. Cache miss: the edge asks the origin
  4. The answer comes back and is cached at the edge
  5. The next request is answered without leaving the region

Chapter 06 · Under pressure

Built to fail well

Everything fails eventually: machines, networks, whole data centres. The craft is deciding in advance what happens when they do. Health checks that notice quickly, traffic that shifts automatically, capacity that's already waiting, and alarms that wake the right person only when it matters.

  1. Traffic grows
  2. An edge location goes dark
  3. Health checks catch it
  4. Traffic shifts to the next-nearest healthy edge
  5. Users never notice

Chapter 07 · New worlds

What I build

Beyond the systems above, I design and ship complete products end to end: architecture, code, infrastructure and the user experience.

  • Commerce platforms & integrations

    Multi-tenant platforms that sit inside online stores and between them and the rest of the business. Checkout and pricing logic that runs at the edge of the platform, and integration services that keep storefronts, ERPs, payments and logistics in agreement: idempotent, retry-safe and observable, across dozens of connectors and 20+ languages.

  • Applied AI & LLM systems

    Production pipelines that turn messy documents into structured, trustworthy data. Vision models extract the facts, personal data is redacted before anything leaves the system, confidence scoring sends only the uncertain cases to a human, and every user has hard cost limits. Plus tool-calling assistants that act, not just answer.

  • Privacy-first data platforms

    Software for the most sensitive records people have. Passkey sign-in, sharing scoped to exactly the right people, isolation enforced by the database itself rather than by application code, and offline-first apps that work the same on web, iOS and Android.

  • Spatial & 3D experiences

    Real-time 3D in the browser: from a floor plan to a walk-through interior with parametric furniture and generated quotes, to the particle system you are scrolling through right now.

  • Engineering that holds up

    How everything above gets built: typed monorepos, strict CI gates, full test coverage, end-to-end tests, and tracing and alerting wired in from the first commit, so systems stay boring in production.

Chapter 08 · The elements

Stack

Languages08

  • Java
  • Go
  • Rust
  • C
  • Python
  • TypeScript
  • JavaScript
  • SQL

Backend & APIs08

  • Node.js
  • Fastify
  • Spring Boot
  • FastAPI
  • REST · OpenAPI
  • GraphQL
  • WebSockets
  • Zod

Frontend10

  • React
  • React Router
  • TanStack
  • Tailwind CSS
  • Radix UI
  • Vite
  • Astro
  • Three.js
  • PWA
  • Capacitor

Data08

  • PostgreSQL
  • Redis
  • DynamoDB
  • Supabase
  • Drizzle
  • Prisma
  • SQLAlchemy
  • S3

Cloud & Infra09

  • AWS
  • Cloudflare Workers
  • Fly.io
  • Railway
  • Docker
  • Kubernetes
  • Terraform
  • Linux
  • nginx

Networking06

  • HTTP · HTTPS
  • Reverse proxies
  • Caching
  • DNS
  • CDNs
  • Failover

AI & LLMs08

  • Claude API
  • Vision extraction
  • Tool calling
  • PII redaction
  • Human-in-the-loop review
  • Cost guards
  • scikit-learn
  • XGBoost

Commerce08

  • Shopify apps
  • Shopify Functions
  • Polaris
  • App Bridge
  • Admin GraphQL
  • Stripe
  • BigCommerce
  • WooCommerce

Security & Identity08

  • SSO
  • OAuth
  • JWT
  • Passkeys · WebAuthn
  • Argon2
  • Access control
  • Provisioning
  • Rate limiting

Quality & Ops08

  • OpenTelemetry
  • Sentry
  • Prometheus
  • Vitest
  • Playwright
  • Testcontainers
  • axe a11y
  • CI/CD
{edu} Dundalk Institute of Technology, Ireland — B.Sc. (Hons) Commercial Computing; B.Sc. Software Development · English & Mandarin

Chapter 09 · Signal

Contact

Say hello.
LinkedIn is the quickest way to reach me.