Overview

TopUpTest is a production SaaS A/B testing platform enabling website owners to deploy experiments, track behavioural events and generate AI-powered optimisation insights. The system captures key conversion metrics including form submissions, button interactions, bounce rate and session engagement, and makes A/B test suggestions via an integrated Gemini LLM engine.

Architecture & Technical Implementation

Architected using a PERN + TypeScript + GraphQL stack, with a distributed backend design separating application logic, event ingestion and billing infrastructure.

• Distributed Node.js Backend: Three independent services — a primary Apollo GraphQL API governing user accounts and experiment configuration, a dedicated REST tracking service for high-volume event ingestion, and a Stripe webhook processor handling subscription lifecycle and billing events.
• Frontend Application: React + TypeScript SPA consuming a typed GraphQL API via URQL, leveraging hooks and context for state management and a generated schema for end-to-end type safety.
• AI Insight Engine: Integrated Gemini LLM API to generate structured A/B test recommendations for users, including prompt design, response parsing and output validation.
• Event Tracking System: Custom client-side tracking script using the Beacon API to reliably transmit behavioural data to the ingestion service with minimal performance impact.
• Relational Data Modelling: Designed and implemented a normalised PostgreSQL schema based on domain modelling of experiments, variants, events and user accounts, with SQL resolvers and stored procedures supporting business logic.
• Infrastructure & Deployment: Deployed across isolated DigitalOcean droplets with Nginx reverse proxy configuration, SSL certificate management, DNS configuration and PM2 process management across staging and production environments.
• Security Hardening: JWT-based authentication, IP rate limiting, UFW firewall configuration, Fail2Ban intrusion protection and hardened server configuration.
• Testing Strategy: Unit testing with Jest + Mock Service Worker for API isolation, and end-to-end coverage with Cypress for experiment workflows and billing flows.