System Design Knowledge Base

A comprehensive collection of system design case studies, architectural patterns, production-grade implementations, and interview preparation resources.

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📖 Glossary & Quick Navigation

mindmap
  root((System Design))
    Case Studies
      Financial Systems
      E-Commerce
      Food Delivery
      IoT & Streaming
      Collaboration
    Patterns
      Communication
      Resilience
      Data
      Messaging
      Deployment
    Implementations
      URL Shortener
      Rate Limiter
      Leaderboard
      OAuth 2.0
      JWT Auth
      Products API
    Resources
      Interview Guide
      Compliance Guide
      Job Search HQ
      Workflow Tools

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🏗️ System Design Case Studies

Financial Systems

Topic	Description	Key Concepts	Links
Financial Clearing House	Interbank settlement system with multilateral netting achieving 93%+ efficiency	Graph algorithms, Two-phase settlement, Saga pattern	📘 Overview • 🏛️ Architecture • 🔄 Flow
Seller Payment System	E-commerce seller payouts with configurable schedules and fee optimization	Exactly-once semantics, State machines, Idempotency	📘 Overview • 🏛️ Architecture • 💾 Data Models
Fintech Data Platform	End-to-end data architecture with CDC, event streaming, and federated queries	CDC (Debezium), Kafka, HTAP, Data Lake	📘 Overview • 📊 E2E Diagram

E-Commerce & Marketplace

Topic	Description	Key Concepts	Links
Merchandise Browsing	Large-scale product discovery for 1M+ DAU with real-time trending	Popularity scoring, Flink streaming, Personalization	📘 Overview • 📊 Diagrams
Uber Cart System	Multi-merchant cart with family accounts and offline-first behavior	CRDT sync, Multi-tenant, Event sourcing	📘 Overview • 🏛️ Architecture • 📱 API
Issue Tracking System	Multi-tenant Jira-like platform for 50M DAU with 10B issues	Row-level security, Elasticsearch, Tenant isolation	📘 Overview • 🏛️ Architecture • 🔍 Search

Food Delivery & Logistics

Topic	Description	Key Concepts	Links
Uber Eats Feed	Restaurant feed with H3 spatial indexing handling 10K+ views/sec	H3 hexagonal grid, Geo-sharding, ML ranking	📘 Overview • 🗺️ Spatial Indexing • 📊 Ranking

Real-Time & Collaboration

Topic	Description	Key Concepts	Links
Collaborative Editor	Google Docs-like editor with CRDTs for 100 concurrent editors	CRDT, WebSocket, Offline-first, Causal consistency	📘 Overview • 🧬 CRDT Design • 🔄 Sync Protocol
Real-Time Leaderboard	Gaming leaderboard for 100M users with global/regional rankings	Redis Sorted Sets, Kafka, WebSocket push	📘 Overview • 🏛️ Architecture • 📊 Redis Deep Dive

IoT & Streaming Systems

Topic	Description	Key Concepts	Links
Trucking Crash Detection	Real-time crash detection for 1M vehicles with <30s notification	Stream processing, ML inference, IoT ingestion	📘 Overview • 🏛️ Architecture • 🧠 ML Pipeline

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📐 Distributed System Patterns

📚 Complete Pattern Reference — Decision flowcharts, trade-off analysis, and implementation examples

API & Communication Patterns

Pattern	When to Use	Trade-offs	Link
REST API	Public APIs, CRUD operations	Simple ↔ Over/under-fetching	📄 Docs
GraphQL	Mobile apps, complex queries	Flexible ↔ Caching complexity	📄 Docs
gRPC	Internal microservices, high performance	Fast ↔ Browser support	📄 Docs
WebSockets	Real-time bidirectional	Low latency ↔ Connection overhead	📄 Docs

Gateway & Routing Patterns

Pattern	When to Use	Trade-offs	Link
API Gateway	Centralized entry point	Single entry ↔ SPOF risk	📄 Docs
Backend for Frontend	Multi-platform clients	Optimized UX ↔ Code duplication	📄 Docs
Aggregator	Composite responses	Reduced round trips ↔ Complexity	📄 Docs

Resilience Patterns

Pattern	When to Use	Trade-offs	Link
Circuit Breaker	Prevent cascading failures	Fail-fast ↔ Implementation complexity	📄 Docs
Retry with Backoff	Handle transient failures	Reliability ↔ Thundering herd	📄 Docs
Bulkhead	Isolate resource pools	Fault isolation ↔ Resource underutilization	📄 Docs
Rate Limiting	Traffic spike protection	System protection ↔ User experience	📄 Docs
Timeout	Prevent hung connections	Responsiveness ↔ False positives	📄 Docs

Data Patterns

Pattern	When to Use	Trade-offs	Link
CQRS	Separate read/write scaling	Performance ↔ Complexity	📄 Docs
Event Sourcing	Audit trails, temporal queries	Complete history ↔ Storage costs	📄 Docs
Saga Pattern	Distributed transactions	Eventual consistency ↔ Coordination	📄 Docs
Outbox Pattern	Reliable event publishing	Guaranteed delivery ↔ At-least-once	📄 Docs
Two-Phase Commit	Strong consistency needed	ACID guarantees ↔ Availability	📄 Docs

Messaging Patterns

Pattern	When to Use	Trade-offs	Link
Pub/Sub	Fan-out notifications	Decoupling ↔ Message ordering	📄 Docs
Message Queue	Work distribution	Reliability ↔ Latency	📄 Docs
Event-Driven Architecture	Reactive systems	Flexibility ↔ Debugging complexity	📄 Docs

Service Discovery & Mesh

Pattern	When to Use	Trade-offs	Link
Service Registry	Dynamic service discovery	Flexibility ↔ Additional infrastructure	📄 Docs
Sidecar	Cross-cutting concerns	Separation of concerns ↔ Resource overhead	📄 Docs
Service Mesh	Complex microservices	Full observability ↔ Operational complexity	📄 Docs

Deployment & Infrastructure

Pattern	When to Use	Trade-offs	Link
Blue-Green Deployment	Zero-downtime releases	Instant rollback ↔ 2x infrastructure	📄 Docs
Canary Deployment	Gradual rollouts	Lower risk ↔ Complexity	📄 Docs
Rolling Deployment	Resource-efficient updates	Simple ↔ Slower rollback	📄 Docs
Feature Flags	Runtime feature control	Flexibility ↔ Tech debt	📄 Docs
Strangler Fig	Legacy migration	Incremental ↔ Longer timeline	📄 Docs
Database Per Service	Microservices data isolation	Autonomy ↔ Distributed complexity	📄 Docs

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🔧 Production Implementations

URL Shortener

Full-stack URL shortener scaling from local to 500M URLs/month globally

Tier	Scale	Architecture
1	Local	SQLite + Single binary
2	Startup (100K/mo)	PostgreSQL + Redis
3	Growth (10M/mo)	Multi-instance + Replicas
4	Scale (100M/mo)	Multi-region + DynamoDB
5	Global (500M/mo)	Edge computing + Sharded

Stack: Rust (Axum) • DynamoDB Global Tables • CloudFront • Terraform • Kubernetes

Resource	Link
Rust Version	📘 README
Java Version	📘 README
Architecture	🏛️ Docs
Security & Compliance	🔒 GDPR/SOC2

Distributed Rate Limiter

High-performance rate limiter for API Gateway (100K-1M RPS)

Features: Sliding window counter • Composite keys (user + endpoint) • Fail-open/closed modes • Circuit breaker integration

Stack: Java 21 (Spring Boot) • Redis Cluster • Resilience4j • Prometheus

Resource	Link
Overview	📘 README
Architecture	🏛️ Docs
Algorithms	🧮 Docs

Real-Time Leaderboard

Gaming leaderboard for 100M users with 50M DAU, supporting global/regional/friend rankings

Features: O(log N) Redis Sorted Sets • WebSocket push notifications • Multiple time windows • Circuit breakers

Stack: Java 21 (Spring Boot) • Redis Cluster • Kafka • PostgreSQL • WebSocket

Resource	Link
Overview	📘 README
Architecture	🏛️ Docs
Redis Deep Dive	📊 Docs
Demo Scripts	🎮 Scripts

OAuth 2.0 Demo

Complete OAuth 2.0 implementation with Authorization Server and Resource Server

Features: Authorization Code + PKCE • Client Credentials • Refresh Tokens • JWT with custom claims • PostgreSQL persistence

Stack: Java (Spring Boot 3.2) • Spring Authorization Server • Spring Security • PostgreSQL

Resource	Link
Overview	📘 README
Postman Collection	📬 Collection

JWT Authentication

Simple JWT auth system with access/refresh tokens

Features: Token rotation • Secure refresh flow • Spring Security integration

Stack: Java (Spring Boot 3.2) • Spring Security • MySQL • jjwt

Resource	Link
Overview	📘 README
Architecture	🏛️ Docs
Postman Collection	📬 Collection

Products API (Cassandra/ScyllaDB)

RESTful CRUD API demonstrating Cassandra/ScyllaDB patterns

Features: CQL operations • Docker Compose setup • Seed data

Stack: Java (Spring Boot) • Apache Cassandra 4.1 • Docker

Resource	Link
Overview	📘 README

Codec Library

MySQL column type codecs with zero-copy decoding (Go)

Features: Text/Binary protocol • Temporal types with timezone • DECIMAL precision • database/sql helpers

Resource	Link
Overview	📘 README
Source	📦 Go Package

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🎓 Interview & Career Resources

System Design Interview Guide

📚 Complete Guide — 12-part comprehensive preparation resource

#	Topic	Description
01	Interview Framework	Step-by-step approach for any interview
02	Requirements & Estimation	Capacity planning basics
02a	Back-of-Envelope (Detailed)	Mental math tricks & calculations
03	Core Building Blocks	DBs, caching, load balancers
04	Scalability Patterns	Sharding, replication, scaling
05	Distributed Concepts	CAP, consistency, consensus
06	Data Storage	SQL vs NoSQL, partitioning
07	Caching Strategies	Patterns, invalidation, CDNs
08	Messaging & Async	Queues, event-driven
09	API Design	REST, GraphQL, gRPC
10	Observability	Monitoring, fault tolerance
11	Common Problems	URL shortener, chat, feed
12	Quick Reference	One-page cheatsheet

Job Search HQ

Complete job search framework with trackers, templates, and guides

Category	Topics	Link
Resume	Quantified achievements, LinkedIn optimization	📄 Resume Guide
Behavioral	STAR stories, EM philosophy	📄 STAR Bank
System Design	Quick reference sheets	📄 Cheat Sheets
LLD	Patterns, problem bank	📄 LLD Guide
Coding	Pattern-based approach	📄 Coding Patterns
Negotiation	Compensation strategy	📄 Negotiation
Tracker	Company research template	📄 Tracker

📚 Full Job Search Guide

Interview Experiences

Company	Type	Link
Agoda	System Design + LLD	📁 Folder
Kuvera	System Design	📁 Folder
Fintech Org	Architecture Review	📁 Folder

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📋 Compliance & Regulations

Global Financial Compliance Guide

📚 Complete Guide — 42 compliance frameworks across 6 regions

Comprehensive reference covering:

Region	Key Regulations
Global	Basel III/IV, FATF, PCI DSS, ISO 27001
North America	SOX, GLBA, BSA/AML, Dodd-Frank, CCPA, NYDFS
Europe	GDPR, PSD2/PSD3, MiFID II, DORA, AMLD 5/6
Asia Pacific	RBI Master Directions, DPDP Act, PIPL, MAS TRM, CPS 234
Middle East	CBUAE, SAMA Cybersecurity, PDPL
Latin America	LGPD, BCB Resolution 4893
Africa	POPIA, SARB, NDPR

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🛠️ Tools & Workflow

Apache Airflow

Workflow orchestration with practical DAG examples

Use Cases: ETL pipelines • ML orchestration • Data quality • Report generation

Resource	Link
Getting Started	📘 README
Core Concepts	📄 Concepts
Best Practices	📄 Guide
Example DAGs	📦 dags/

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🗺️ Learning Paths

Path 1: System Design Fundamentals

flowchart LR
    A[Interview Guide] --> B[Patterns Reference]
    B --> C[URL Shortener]
    C --> D[Rate Limiter]
    D --> E[Leaderboard]

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1. Foundation: System Design Interview Guide
2. Patterns: Distributed Patterns
3. Build: URL Shortener
4. Scale: Rate Limiter
5. Real-time: Leaderboard

Path 2: Authentication & Security

flowchart LR
    A[JWT Auth] --> B[OAuth 2.0]
    B --> C[Compliance Guide]
    C --> D[Seller Payments]

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1. Basics: JWT Authentication
2. OAuth: OAuth 2.0 Demo
3. Compliance: Financial Compliance Guide
4. Apply: Seller Payment System

Path 3: Real-Time Systems

flowchart LR
    A[Event-Driven Patterns] --> B[Collaborative Editor]
    B --> C[Uber Eats Feed]
    C --> D[Crash Detection]

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1. Foundation: Messaging Patterns
2. Collaboration: Collaborative Editor
3. Geo-Spatial: Uber Eats Feed
4. IoT Streaming: Crash Detection

Path 4: Multi-Tenant Systems

flowchart LR
    A[Data Patterns] --> B[Issue Tracker]
    B --> C[Seller Payments]
    C --> D[Clearing House]

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1. Patterns: Data Patterns
2. Multi-Tenant: Issue Tracking System
3. Payments: Seller Payment System
4. Finance: Clearing House

Path 5: Interview Preparation

flowchart LR
    A[Interview Guide] --> B[Quick Reference]
    B --> C[Case Studies]
    C --> D[Mock Practice]

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1. Guide: Interview Framework
2. Reference: Cheatsheet
3. Study: Any case study from above
4. Review: Interview Experiences

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📊 Pattern Cross-Reference

Pattern	Used In
Event Sourcing / CDC	Fintech Data Platform, E-Commerce, Collaborative Editor
CQRS	E-Commerce, Uber Eats Feed, Issue Tracking
Saga Pattern	Financial Clearing House, Seller Payments
Exactly-Once Semantics	Clearing House, Seller Payments, Leaderboard
CRDT	Collaborative Editor
Redis Sorted Sets	Leaderboard, Rate Limiter
Batch + Real-time (Lambda)	E-Commerce, Crash Detection
H3 Spatial Indexing	Uber Eats Feed
Circuit Breaker	Rate Limiter, Seller Payments, Leaderboard
Multi-Tenancy (RLS)	Issue Tracking System
WebSocket	Collaborative Editor, Leaderboard
OAuth 2.0 / JWT	OAuth 2.0 Demo, JWT Auth
Sharding / Partitioning	All case studies

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🚀 Quick Start

Run OAuth 2.0 Demo

cd oauth2-demo && ./run.sh
# Auth Server: http://localhost:9001
# Resource Server: http://localhost:8080

Run Leaderboard Demo

cd leaderboard
docker-compose up -d redis zookeeper kafka postgres
./mvnw spring-boot:run
./scripts/demo-data.sh

Run Financial Clearing House Demo

# Python
cd financial-clearing-house/src/python && python3 demo.py

# Java
cd financial-clearing-house
mkdir -p target && find src/java -name "*.java" | xargs javac -d target
java -cp target com.clearinghouse.SettlementApp

Run URL Shortener

cd url-shortener && docker-compose up -d
# API available at http://localhost:8080

Run Rate Limiter

cd rate-limiter && docker-compose up -d redis && ./mvnw spring-boot:run

Run JWT Auth

cd jwt-auth && docker-compose up -d --build
# API available at http://localhost:8080

Run Products API (Cassandra)

cd products-api && docker-compose up -d --build
# API available at http://localhost:8080

Run Airflow Examples

cd apache-airflow && docker-compose up -d
# UI at http://localhost:8080 (admin/admin)

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📝 License

MIT — See LICENSE for details.

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Built for engineers who want depth over breadth in system design.