System-Design

Last week, I was assigned to implement SSO (Single Sign-On) for a project called HappyClub. The backend runs on Java Spring Boot, and locally everything worked just fine — smooth SSO redirect, valid tokens, no errors. But as soon as I deployed to the staging environment (which runs 2 pods on Kubernetes), I hit two painful issues. I wasted quite a bit of time debugging because I didn’t read the Spring Security docs carefully at first 😅. ...

Designing a system for 10 users is very different from designing one for 10 million. Scaling isn’t just about “adding more servers” — it’s an architectural challenge: where the data flows, how it’s processed, and how the system holds under pressure. In this article, I’ll share a step-by-step approach to building a scalable system — not through formulas or dogma, but through real-world design thinking shaped by hands-on experience. 1. Start with a Single Server In the early stage, the entire system often runs on a single machine. ...