Software Engineering student at FPT University, Hanoi. I build and operate cuongthai.com — a bilingual (VI/EN) learning platform: courses, an AI tutor, a code lab, an exam room, and companion iOS + desktop apps.
It isn't a tutorial project. It runs in production on a VPS I administer myself, and I'm the one who has to fix it when it breaks at 2am.
How I build: I design the system and break the work into tasks, an AI coding agent (Claude Code) writes much of the code, and I review it, test the real behaviour, deploy it and keep it running.
| Backend | Node.js · Express · TypeScript · PostgreSQL + Prisma · 319 tables, 150 migrations · Redis · Socket.IO |
| Web | Next.js (App Router) · React · Tailwind |
| Mobile | iOS + iPadOS — SwiftUI, ~111k lines, shipped to TestFlight (source) |
| Desktop | Electron — 130+ releases for macOS, Windows and Linux, delivered by auto-update |
| Infra | Docker · GHCR · nginx · self-administered VPS · images built on a home server, post-deploy smoke tests, nginx config verified from inside the container and reverted automatically on failure |
| AI | One gateway over several LLM providers with per-feature model routing, per-user token quotas and daily spend limits · a self-hosted Qwen model on a home GPU behind a priority queue |
Scale of the running system: 4,300+ commits since June 2026 · 592 published courses · 12,100 lessons · 1,058 videos with bilingual subtitles (330,936 aligned sentences, 4.8M words).
Honest note: this is a personal platform, not a startup — about 70 users. What I'm showing is the engineering, not traction.
These are the ones that taught me the most — all of them share a shape: something reported success while doing nothing.
A Docker bind-mount that read the old file forever
Changed nginx.conf, reloaded, got a green result — and nothing changed. Twice.
Docker binds a single file by inode, not by path. The deploy script
replaced the file with mv, which points the path at a new inode, so the
container kept reading the old one: nginx -t validated the old config,
reload reloaded the old config, the script reported OK.
Fix: write in place (cat new > conf), never mv/rsync/sed -i. Then
verify by comparing sha256 on the host against
docker exec … sha256sum /etc/nginx/nginx.conf — because "written" is not
"what the container reads".
An sshd setting that applied only half the time
Wrote PasswordAuthentication no into 70-no-password.conf. sshd -t green,
reload green, exit 0 — and sshd -T still said yes.
sshd_config takes the first value it reads, and the *.conf glob is
alphabetical: a pre-existing 50-cloud-init.conf had already won. The
PermitRootLogin line in the same file did apply — because nothing competed
for it. Half working is the signature of an ordering collision, not a syntax
error.
Fix: prefix 01-. Verify with sshd -T (effective value), never cat of the
file you just wrote.
A build that was green all the way to a 7-minute outage
An image built outside compose picked up the default Dockerfile instead of
Dockerfile.backend. Result: an Alpine (musl) base carrying a Prisma engine
compiled for debian-openssl-3.0.x (glibc). Build green, push green, swap
green — then the backend restart-looped and the API was down.
Fix: a libc ↔ engine compatibility gate that runs before the push. Lesson: a green build does not mean a runnable image.
A page that hung on its loading screen with no error at all
The 3D playground span two debugging sessions stuck on "loading", console clean, network clean.
Next.js snapshots the contents of public/ at server start. Rebuilding the
playground changed the bundle's content hash, so the running server returned
404 for a file that was physically on disk — no JS ran, and the loading screen
is plain HTML, so there was nothing to see fail.
Fix: restart Next after touching public/**. And kill the old server by
port — Node renames the process to next-server, so pkill -f "next start"
matches nothing and you end up debugging a zombie.
A link that rendered perfectly and did nothing
Added clickable [2:19] timestamps to AI answers so tapping one seeks the
video. Underline, hover colour, cursor — all correct. Clicking did nothing.
react-markdown runs defaultUrlTransform on every href and allows only
http/https/mailto/xmpp plus relative paths. A custom tua://139 scheme is
silently replaced with an empty string. Measured, rather than guessed:
defaultUrlTransform('tua://139') // → ''
defaultUrlTransform('#tua-139') // → '#tua-139'Fix: anchor form #tua-139, intercepted with a delegated click handler.
The habit underneath all of these: HTTP 200, exit 0 and a green log are not
evidence. I verify with the thing that would differ if the change hadn't
worked — sshd -T, sha256sum from inside the container, curl -I, the route
table next build prints.
| api-backend | The platform monorepo — backend, web, desktop, infra, deploy tooling |
| cuongthai-ios | The native SwiftUI app for iPhone and iPad — PencilKit notebook, 3D workshop with AR, WebRTC calls, widgets |
| cuongthai-desktop | Release channel for the Electron app — installers and the auto-update feed |
| CuongHoangDev-V2 | The project before cuongthai.com: Spring Boot 3 + Flyway API, TypeScript/React front end, 287 commits in 12 days · live demo |
| Library-Management-System | Spring Boot 3.4 (Java 21) + React — "one open loan per copy" enforced by a PostgreSQL partial unique index |
| Homestay-Booking-API | TypeScript REST API practice project with a Vitest test suite |
| Restaurant-Reservation-App | Flutter client over a Node/Express + PostgreSQL API — table booking with SKIP LOCKED |
Java + Spring Boot — the dominant enterprise backend stack in Vietnam — and deepening my JavaScript/React fundamentals by writing more of it by hand.
- 🌐 cuongthai.com
- 📍 Hanoi, Vietnam (GMT+7) · open to internships, part-time roles and small freelance projects — deploying and fixing Next.js / Node.js apps