Data Consistency in Microservices — Saga Pattern
One-liner: In microservices, you can't use a single database transaction across services — the Saga pattern breaks it into a sequence of local transac…
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Building Production AI Systems(Final)
Designing AI Systems That Outlive Today's Models If there's one lesson this series has taught me, it's this: Don't build your application around a mod…
LLD Data Structures in Design Context: Real-World HashMaps — Sessions, Caches, Indexes and Design Trade-offs
"A HashMap is not valuable because it is fast. It is valuable because it makes the right things fast." In the previous articles, we built our understa…
The Day the Warehouse Burned: Lessons in Cross-Border System Resilience
A fire in a fulfillment center on the far side of the world. It didn't make headlines. But for a cross-border e-commerce operation， it was a quiet cat…
How to Destroy a Project in 5 Steps
The following guide is provided as a public service. If your goal is to maximize chaos, ensure total loss of accountability, and achieve legendary sta…
From Payment to Shipping: How We Built a Cross-Border Order State Machine That Solved Idempotency and Callback Chaos
When your payment gateway fires the same "paid" webhook three times, your logistics API calls back with "shipped" before payment is confirmed, and the…
When to refactor vs rewrite
A decision tree for grown engineers Every engineering team eventually faces the same dramatic sentence. We should just rewrite this. It is usually sai…
Building Microservices Like a Professional: Lessons I Wish I Learned Earlier
If you've ever started a microservices project by splitting a monolith into dozens of tiny services, you've probably experienced this: "We have micros…
Stop Using Round-Robin: High-Throughput Java Virtual Thread Routing with P2C
Stop Using Round-Robin: High-Throughput Java Virtual Thread Routing with P2C Virtual threads allow Java microservices to comfortably run 50,000 concur…
Beyond the Model: Building the AI Harness
The AI Harness is becoming the real engineering layer. Everyone is talking about AI Agents. I think we're missing the more important piece. The AI Har…
I Found the LeetCode for System Design Interview, and It's Awesome
Disclosure: This post includes affiliate links; I may receive compensation if you purchase products or services from the different links provided in t…
The Follow-Up Questions That Decide System Design Interviews (And How to Pre-Empt Them)
Where Interviews Are Actually Won Ask interviewers where candidates separate, and almost none will say "the initial design." Prep materials have conve…
What actually belongs in an architecture decision record (and what doesn't)
Most architecture decision records fail for the opposite reason people think. The issue usually isn't that teams forget to write them. It's that the o…
trelix v2.7 to v2.9: The Release Where the Pipeline Itself Became the Product
On 2026-07-09 I shipped trelix v2.7.0. The architecture felt done — seven retrieval legs, a knowledge graph, an agentic loop. Then I opened the GitHub…
Polling: When "Simple" Starts Sending Millions of Requests
Imagine you're building a SaaS platform. Nothing fancy. Just a notification bell in the top-right corner. When someone receives a new message, complet…
The Backend Patterns I Wish I Learned Earlier
When I started building backend systems, I thought becoming a better developer meant learning more technologies. A new framework. A new database. A ne…
Designing Software That Gets Faster as It Gets Bigger
One of the biggest myths in software engineering is that growth inevitably makes software slower. We almost expect it. More users mean more database q…
Why your Cache won't save you from a "Thundering Herd" 🐂
We've all been there: you add Redis, and your latency drops. But have you planned for the Thundering Herd? The Problem A Thundering Herd occurs when a…
Designing a Notification System That Doesn't Fall Apart
Every application eventually reaches the point where it needs notifications. At first, it feels simple. A user signs up? Send an email. Someone likes …
Building Reliable Event-Driven Systems: Event Schemas, Versioning, Contract Testing and Events vs Commands (5/5)
In this final article, we're going to explore Production practices 22. Events Are Delivered, Not Guaranteed A common misconception in event-driven arc…
Shared Context Patterns for Multi-Agent Systems
You've got three agents running at the same time. One pulls customer data. Another generates a response. The third decides whether to escalate. Then a…
How We Split a Legacy Monolith Into Microservices Without a Single Outage
8 min read · telecom provisioning platform, 30M+ subscribers Most companies avoid migrating their monolith for one reason: they imagine it as a single…
Reversal Architecture in Distributed Financial Systems: Compensation, Liability, and Irreversible Side Effects
Abstract Distributed financial systems frequently treat reversal as a secondary state attached to an otherwise completed transaction. A payment succee…
We fixed a hidden bug in a system processing 10M+ messages a day.
9 min read · warehouse execution system, global retail & manufacturing A few years ago I worked on a warehouse execution system (WES) — the softwa…
System Design - Building an Experiment Service
So I tried to build an experiment service (here's every wrong turn first) Say you run a website and have a hunch a new signup page converts better tha…
How Netflix Doesn't Crash During Peak Hours (Cloud Concepts) ! 😱
Millions of people open Netflix at the same time—during weekends, evenings, or when a new season drops. Despite this massive traffic, users usually ex…
LLD Domain Modeling: The Only Cheat Sheet You Actually Need (Interview + Real System Design)
After going through entities, invariants, state machines, aggregates, bounded contexts, and full systems like Ride Sharing, BookMyShow, and Amazon Car…
LLD Domain Modeling: The Complete Mental Framework (How to Think in Any System Design Problem)
This is the final consolidation of everything in Domain Modeling. If you understand this structure deeply, you don’t need to memorize LLD patterns any…
LLD Domain Modeling: How Real Systems Evolve Over Time (Versioning, Change & Refactoring Reality)
One thing beginner LLD tutorials rarely show is this: real systems never stay in their “initial design”. They evolve constantly: new features get adde…
LLD Domain Modeling: When NOT to Use Domain Modeling (Very Important Reality Check)
Up to now, domain modeling may feel like the answer to everything: entities aggregates invariants bounded contexts state machines But strong engineers…