Backend Engineer — focused on scalable backend systems, production-oriented architecture, and real-world transactional workflows.

I enjoy building systems that go beyond CRUD — focusing on consistency, domain modeling, backend architecture, and infrastructure-oriented engineering.

• Scalable backend systems
• Domain-Driven Design (DDD)
• Authentication & identity infrastructure
• Transactional workflows & concurrency
• Consistency under real-world edge cases (price drift, stale data, race conditions)
• Caching strategies
• E-commerce architecture
• Production deployment & infrastructure

Architecture docs → · source private

A production-oriented marketplace built solo — 215+ REST endpoints, 107K+ LOC — and deployed to production.

• modular monolith with microservice-ready domain boundaries
• variant-first catalog model (persists only purchasable variants — no Cartesian-product explosion)
• cart validation engine with price-drift and stock reconciliation
• snapshot-based checkout with atomic, database-level inventory reservation
• domain events for cross-domain consistency without tight coupling
• bilingual (Arabic / English) PostgreSQL full-text search
• standardized read model with a Caffeine cache and event-driven eviction
• delivery workflows and PostGIS geospatial addressing

Tech: Java · Spring Boot · PostgreSQL · PostGIS · Caffeine · Flyway · Docker · Nginx · React · Next.js

Public repo →

A multi-tenant marketplace for the handmade economy, built with a five-person team — I led backend architecture and deployment.

• multi-tenant backend: 100+ seller companies with strict data isolation
• wallet / escrow with deposit-hold logic for pre-order flows
• in-stock and pre-order product types, each with its own lifecycle
• Arabic full-text search (tsvector + GIN) and JSONB attribute modeling
• load-validated with Apache JMeter at 300 concurrent users — search ~145 ms (p95 280 ms), order creation ~234 ms

Tech: Java · Spring Boot · PostgreSQL · React · Docker · Nginx · AWS S3

Repo →

An identity starter for developers who want full ownership of their auth layer without adopting a heavy IAM product.

• JWT authentication and OAuth2 login
• opaque refresh tokens with rotation
• guest sessions and device-aware flows
• UUID-based public / internal identity mapping
• rate limiting and a full documentation suite

Tech: Java · Spring Boot · Spring Security · PostgreSQL · Flyway · Docker

Backend — Java 21–25 · Spring Boot · Spring Security · Hibernate / JPA · Flyway Database & Infrastructure — PostgreSQL · PostGIS · Caffeine · Redis · Docker · Nginx · Linux Architecture — Domain-Driven Design · Modular Monolith · Domain Events · Transactional Modeling · Database-Level Inventory Reservation · Read-Model Caching Frontend — React · Next.js · Tailwind CSS

Backend engineering isn't about writing endpoints. It's about:

• designing correct systems
• understanding trade-offs
• handling real-world edge cases
• building maintainable architecture
• thinking beyond frameworks

• LinkedIn — https://linkedin.com/in/mohamed-alhajeen
• GitHub — https://github.com/mohammadAlhajeen
• Email — hajeen595@gmail.com