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A production-grade system-design walkthrough for absorbing a 50x, 48-hour Black Friday traffic spike: predictive pre-scaling and horizontal auto-scaling, virtual waiting rooms for graceful load shedding, circuit breakers and bulkheads around the payment gateway, atomic conditional inventory decrement, a Kafka-buffered async order pipeline, layered CDN+cache+read-replica offload protecting the primary database, and…
Designing “Who Viewed Your Profile” with near real-time updates A full walkthrough of how professional networking platforms track, aggregate and surface profile-view activity — near-instantly, at hundreds of millions of users, without drowning the system in write traffic. 01 · History02 · Problem03 · Capacity04 · Architecture05 · Capture06 ·…
Designing a Dynamic Pricing System A from-first-principles walkthrough of how large e-commerce and marketplace platforms adjust prices in near real time from demand, live inventory, and competitor pricing — architecture, data flow, scaling, reliability, and security. 01 · Intro02 · Problem03 · Concepts04 · Architecture05 · Internals06 · Algorithms07 ·…
A production-grade system-design walkthrough for detecting compromised public-figure accounts from anomalous posting behaviour: per-account behavioural baselining across temporal, content, session, and interaction features; ensemble risk scoring with high-confidence rule overrides; a tiered response ladder (passive log → flag → step-up auth → temporary hold and page); human-in-the-loop review; and fail-toward-caution…
Designing a system that spots viral content before the crowd does A complete, ground-up walkthrough of how to build a platform that watches engagement signals as they happen and flags posts that are about to explode — minutes or hours before a human would ever notice. 01 · Why It…
A complete system design walkthrough for a verified badge identity-verification program at scale: applicant intake, encrypted evidence storage, asynchronous fan-out pipeline (document forensics, liveness/face-match, deduplication, eligibility, risk scoring), three-lane decision routing (auto-approve / human review / auto-reject), badge issuance, tamper-evident audit log, appeals, and data-minimising retention — with inline SVG…
Designing a Real-Time Sales Tax Calculation System Across Thousands of US Jurisdictions A marketplace tax engine that is instant, correct, and survives one million requests a minute — built from first principles through to production concerns. 01 · Intro02 · History03 · Problem04 · Core Concepts05 · Architecture06 · Internals07…
A complete system design walkthrough for a Try Before You Buy apparel marketplace: saga-coordinated trial orders, card authorisation holds, soft and hard inventory reservation, order and return state machines, automated pickup scheduling, courier anti-corruption adapters, warehouse QC, refund and restock flow, capacity estimation, security, and fraud prevention — illustrated with…
Designing a Triangulation Fraud Detection System A complete, from-first-principles walkthrough of how to design a real-time system that catches “triangulation fraud” — where a seller lists items they do not own and fulfils orders using another retailer’s stolen payment details — at a scale of millions of requests per minute.…
Designing a Platform-Wide “Trending Now” Page That Updates in Seconds A complete, ground-up walkthrough of how to build a real-time trending system — one that watches hundreds of millions of events a minute across an entire platform and reflects a genuine shift in global attention on the page within seconds,…