Prolox

Prolox runs a multi-store retailer in Nairobi: a Windows POS for cashiers, a public storefront with self-checkout, and a CRM for stock, stores, and reporting. I started as an intern in December 2020, when sales were still a manual workflow. I came back in 2023 to build the transactional core — an Electron POS, a Next.js storefront, and a REST API on MongoDB. That stack handled over a million transactions for 1,750+ customers, and by 2025 it had outgrown itself. I rebuilt the platform on my own, without closing the shop for a day, onto a single 2 vCPU / 2 GB server. I maintain it.

The backend is Spring Boot 4 and Java 21 — 28 controllers across 20 domain modules — on PostgreSQL 16 with 24 Flyway migrations. The 2 GB budget decided most of the design. Email goes through a Postgres outbox rather than Redis or a queue: one fewer process to run, and a send either commits with the business write or does not happen. Receipt PDFs render in a small Node sidecar with no internet access at all, called off the request path.

The rest is unglamorous and deliberate. Argon2 hashing with a bcrypt fallback so migrated accounts still log in. CSRF double-submit cookies, and sessions scoped per client so the POS cannot use a CRM token. Server-sent events for live sales. Caddy for HTTPS and health-checked deploys. And a parity harness that replays requests against the old system and diffs the answers, so the migration cannot quietly change behavior.

The cutover landed without anyone noticing, which is the whole point of the parity harness. The platform in production today — Spring Boot backend, Next.js storefront, React CRM, self-updating Electron POS, PDF sidecar — runs on the single server it was designed for, with nightly backups off-box. Intern in 2020, product developer in 2023, sole author and maintainer now.