Real Decisions. Real Systems.
Deep dives into architectural decisions at Discord, Shopify, Netflix, Notion, GitHub, and more. Understand the trade-offs that shaped production systems used by millions.
Discord
Discord's Read States: Rewriting a Go Service in Rust
Discord's Read States service tracks which messages each of 150M users has read. It was written in Go and suffered periodic latency spikes caused by garbage collection pauses. The team rewrote it in Rust — not for speed, but for predictable, GC-free memory management. The result was a 5x improvement in worst-case latency.
Shopify
Shopify's Modular Monolith: Avoiding Microservices Complexity
How Shopify tamed a 2M-line Rails codebase without microservices
Notion
Notion's Postgres Migration: 10x Query Speed by Rethinking the Schema
How Notion escaped slow JSONB queries by moving to typed columnar storage
GitHub
GitHub's Migration from MySQL to Vitess
Sharding 28TB of MySQL data without downtime using Vitess
Netflix
Netflix's Chaos Engineering: Building Resilience by Breaking Things
How Netflix intentionally kills production services to find failure modes before customers do
Slack
Slack's WebSocket Gateway: Serving 1M Concurrent Connections
How Slack scaled real-time messaging to millions of simultaneous users
Uber
Uber's Decision to Move from Postgres to MySQL
Why Uber left PostgreSQL's MVCC model for MySQL's replication architecture
System Design Interview
Design a Photo Sharing App (Instagram-Style)
Users upload photos, others comment and react — how do you store, sort, and serve it all at scale?
System Design Interview
Design a URL Shortener (bit.ly)
6-character codes that redirect billions of times a day — deceptively simple to design wrong
System Design Interview
Design a Real-Time Chat App (WhatsApp / Messenger)
1-to-1 and group messaging, online presence, read receipts, and message delivery guarantees
System Design Interview
Design a Ride-Sharing App (Uber / Lyft)
Matching riders to nearby drivers in real time — geospatial indexing, supply/demand pricing, trip state machines
System Design Interview
Design a Video Streaming Platform (YouTube / Netflix)
Upload, transcode, store, and stream terabytes of video to 2 billion users — which parts are hardest?
System Design Interview
Design a Social News Feed (Twitter / LinkedIn)
Fan-out on write vs fan-out on read — the core trade-off that shapes every social feed architecture
System Design Interview
Design a Hotel Booking System (Booking.com)
Inventory management, double-booking prevention, and search across 1M+ properties
System Design Interview
Design a Food Delivery App (Uber Eats / DoorDash)
Three moving pieces: customer ordering, restaurant accepting, driver pickup — how do you coordinate them?
System Design Interview
Design a Push Notification System
Sending 10 billion notifications a day across iOS, Android, and email — reliably, without duplication
System Design Interview
Design a Search Autocomplete System (Google / Amazon)
Typing 'iph' shows 'iPhone 15' in <100ms — trie, prefix cache, or Elasticsearch?
System Design Interview
Design a Rate Limiter
Token bucket, leaky bucket, fixed window, sliding window — which algorithm and where does the counter live?
System Design Interview
Design a Collaborative Document Editor (Google Docs)
Two users edit the same paragraph simultaneously — how do you merge their changes without losing either?
System Design Interview
Design a Membership Benefits & Verification Platform
100K+ members across 9 organisations — one API to verify membership, personalise benefits, and drive engagement without spamming
System Design Interview
Design a Real-Time Bed Logistics System (Municipal Healthcare)
Hundreds of care homes, thousands of beds, one dashboard — give municipalities live capacity visibility without overwriting clinical data
System Design Interview
Design a Clinical NEWS Score Calculator API
An endpoint that takes vital measurements, validates them, scores them against clinical ranges, and returns a risk score — safely and extensibly
System Design Interview
Design a Digital Worker Identity & Compliance Platform
Issue, verify, and revoke digital work IDs across thousands of employers, sites, and workers — in real time and offline
System Design Interview
Design a Free Local Gig Marketplace (Small Jobs Platform)
A zero-fee platform where students, refugees, and households find each other for babysitting, cooking, pet care, and painting — trust built through reviews alone
System Design Interview
Design a Healthcare Patient Operations Platform (AWS Serverless)
Answering every patient call, booking into 50+ EHRs, running recall campaigns — all on Lambda, DynamoDB, API Gateway, and S3. Here's how to design it and where the architecture breaks.
Learn the Pattern, Not Just the Story
Each case study connects back to the underlying concept — CAP theorem, MVCC, event loops, sharding, module boundaries. Study the decisions, then explore the deep-dive courses.
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