Enterprise-Scale Source Code for 4 Real-World Projects: Flash Sale, Product Catalog, Payment System, and DDD Implementation

The author has written five technical columns; source code for four of them is now publicly available, and the remaining member‑only column is still being updated.

Flash Sale System for 60 Million Members (Real‑World Implementation)

Previously serving as a senior R&D manager at a chain company with 60 million members, the author built a core flash‑sale system. Unlike many tutorials that stop at theoretical principles or simple demo apps, this column provides a complete micro‑service solution that has withstood real production traffic at that scale. All code is verified to run and can be deployed directly to production.

Product System Supporting Hundreds of Millions of Users and Million‑Level Concurrency

While working as a senior Java developer at an internet company serving several hundred million users, the author helped design the core C‑end product system that powers the homepage, search, detail pages, cart, order, favorites, and recommendation features. The system runs on 32 machines and has handled peaks of 700 k concurrent read requests during major promotions. The column goes beyond typical CRUD and Redis‑cache discussions, addressing challenges such as multi‑gigabyte product data that cannot fit into JVM heap, frequent schema changes without DDL, and promotion‑time spikes that can starve ordinary requests. It delivers a full technical solution that survived real‑world high‑traffic events.

Payment System Handling Over One Hundred Million Users and 500 k Daily Transactions

This payment platform serves more than 100 million registered users and processes about 500 k payment requests each day. It integrates multiple channels—including WeChat Pay, Alipay, wallet balance, free cards, international payments, and POS QR‑code scans—covering the entire flow from request entry to reconciliation. The column explains how to design a system that can simultaneously manage seven or eight active channels and support composite payments, problems that rarely appear in demo projects but cause real incidents and urgent fixes in production.

Three‑Year Journey of Applying Domain‑Driven Design in a Technical Team

Three years ago, the CTO mandated that all micro‑services adopt Domain‑Driven Design (DDD). Starting from zero, the author spent three years iterating, documenting code structures, design decisions, and pitfalls. The column demonstrates the migration step‑by‑step, beginning with database tables and gradually refactoring a traditional three‑layer module into a DDD‑structured service. Each DDD concept—aggregate root, entity, value object, domain service, application service, domain event, bounded context—is introduced through concrete code problems, letting readers see the code first and then understand the concept.

The author invites readers to discuss any technical or career‑related issues and promises a prompt response. Thanks are extended to all subscribers.