System Design Quest Sheet
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 1 | URL Shortener (bit.ly) | Classic | todo | Base62, hash collisions, redirect latency | |
| 2 | Twitter / Social Media Feed | Classic | todo | Fan-out on write vs read, timeline | |
| 3 | Classic | todo | Photo storage, explore, hashtag index | ||
| 4 | WhatsApp / Chat Messaging System | Classic | todo | WebSocket, message ordering, E2EE | |
| 5 | Uber / Ride-Sharing System | Classic | todo | Geohash, supply-demand matching | |
| 6 | Netflix / Video Streaming Platform | Classic | todo | CDN, adaptive bitrate, personalisation | |
| 7 | YouTube | Classic | todo | Upload pipeline, transcoding, comments | |
| 8 | Dropbox / Google Drive (File Sync) | Classic | todo | Block dedup, delta sync, chunking | |
| 9 | Google Docs (Real-Time Collaborative Editing) | Classic | todo | OT vs CRDT, conflict-free merges | |
| 10 | Search Engine (Google-scale) | Classic | todo | Crawl → index → rank → serve | |
| 11 | Google Maps / Routing Engine | Classic | todo | Dijkstra, A*, road graph sharding | |
| 12 | Web Crawler | Classic | todo | Politeness, dedup, frontier scheduling | |
| 13 | Recommendation System (end-to-end) | Classic | todo | Collaborative filtering, two-tower, serving | |
| 14 | Notification Service (email, push, SMS at scale) | Classic | todo | Fanout, deduplication, delivery tracking | |
| 15 | Rate Limiter | Classic | todo | Token bucket, sliding window, Redis | |
| 16 | Distributed Cache | Classic | todo | Eviction policies, clustering, consistency | |
| 17 | Key-Value Store (Redis / DynamoDB internals) | Classic | todo | LSM tree, WAL, consistent hashing | |
| 18 | Distributed Message Queue (Kafka) | Classic | todo | Partitions, offsets, consumer groups | |
| 19 | Logging & Metrics System (Datadog / ELK) | Classic | todo | Structured logs, TSDB, alerting | |
| 20 | Distributed File System (HDFS / GFS) | Classic | todo | NameNode, replication, rack awareness |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 21 | Payment Processing System | Fintech | todo | Idempotency, saga, PCI DSS | |
| 22 | Digital Wallet | Fintech | todo | Balance model, top-up, withdrawal | |
| 23 | Money Transfer System (Venmo / Wise / Moniepoint) | Fintech | todo | Cross-border, FX, settlement rails | |
| 24 | Fraud Detection System | Fintech | todo | Rule engine + ML, real-time scoring | |
| 25 | Card Authorization System | Fintech | todo | Issuer, network, sub-100ms auth | |
| 26 | Ledger / Double-Entry Bookkeeping System | Fintech | todo | Immutable entries, balance integrity | |
| 27 | Reconciliation System (two financial systems) | Fintech | todo | Eventual consistency, diff engine | |
| 28 | KYC / AML Onboarding Flow | Fintech | todo | Watchlist, PEP screening, risk scoring | |
| 29 | High-Throughput Transaction Processing System | Fintech | todo | LMAX Disruptor, mechanical sympathy | |
| 30 | Currency Conversion System | Fintech | todo | FX rate feed, rounding, audit trail | |
| 31 | Banking Core — Account Balances at Scale | Fintech | todo | ACID at scale, regulatory reporting |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 32 | Amazon — Catalog, Search & Checkout | E-Commerce | todo | Product graph, ranking, checkout saga | |
| 33 | Flash Sale / High-Contention Inventory | E-Commerce | todo | Thundering herd, queue, fairness | |
| 34 | Shopping Cart (multi-session, multi-device) | E-Commerce | todo | Merge strategies, guest → auth | |
| 35 | Inventory Management System (multi-warehouse) | E-Commerce | todo | Oversell prevention, reservation TTL | |
| 36 | Price Comparison Engine | E-Commerce | todo | Crawl-and-normalize, ranking, freshness | |
| 37 | Coupon & Promotion Engine | E-Commerce | todo | Rule DSL, stacking, abuse prevention | |
| 38 | Airbnb — Search, Booking & Availability | E-Commerce | todo | Geo search, calendar blocking, pricing | |
| 39 | Order Management System | E-Commerce | todo | State machine, fulfilment pipeline | |
| 40 | Loyalty / Points & Rewards System | E-Commerce | todo | Ledger, expiry, redemption |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 41 | Movie Ticket Booking System (BookMyShow) | Booking | todo | Seat lock, payment window, concurrency | |
| 42 | Hotel Booking System | Booking | todo | Availability calendar, overbooking policy | |
| 43 | Airline Reservation System | Booking | todo | PNR, seat classes, fare rules | |
| 44 | Restaurant Reservation System (OpenTable) | Booking | todo | Table inventory, waitlist, no-show | |
| 45 | Calendar & Scheduling System (Calendly) | Booking | todo | Availability slots, timezone, conflict |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 46 | Live Video Streaming Platform (Twitch) | Real-Time | todo | Ingest, transcode, CDN edge, chat | |
| 47 | Live Sports Scores System | Real-Time | todo | Push vs poll, SSE, fan-out | |
| 48 | Online Multiplayer Game Backend | Real-Time | todo | State sync, authoritative server, lag comp | |
| 49 | Stock Trading Platform | Real-Time | todo | Order matching, LMAX, market data feed | |
| 50 | Real-Time Analytics Dashboard | Real-Time | todo | Kafka + Flink, OLAP, query latency | |
| 51 | Collaborative Whiteboard | Real-Time | todo | CRDT, WebSocket, cursor presence |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 52 | CI/CD System | Infra & DevTools | todo | Pipeline DAG, artifact store, rollback | |
| 53 | Feature Flag Service (LaunchDarkly) | Infra & DevTools | todo | Progressive rollout, targeting rules | |
| 54 | Configuration Management System | Infra & DevTools | todo | Hot reload, versioning, audit | |
| 55 | Secrets Management System (Vault) | Infra & DevTools | todo | Dynamic secrets, lease renewal, KMS | |
| 56 | API Gateway | Infra & DevTools | todo | Auth, routing, throttling, observability | |
| 57 | Service Registry & Discovery | Infra & DevTools | todo | Consul, Eureka, health checks | |
| 58 | Distributed Job Scheduler (cron at scale) | Infra & DevTools | todo | Exactly-once, leader election, sharding | |
| 59 | Workflow Engine (Airflow / Temporal) | Infra & DevTools | todo | DAG execution, retries, durable state |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 60 | Content Delivery Network (CDN) | Content & Media | todo | PoP placement, cache hierarchy, purge | |
| 61 | Image Hosting & Serving System | Content & Media | todo | On-the-fly resize, WebP, CDN offload | |
| 62 | Podcast Hosting Platform | Content & Media | todo | Audio storage, RSS, analytics | |
| 63 | News Feed Aggregator | Content & Media | todo | RSS crawl, dedup, personalisation | |
| 64 | Content Moderation System | Content & Media | todo | ML classifier + human review pipeline | |
| 65 | Comment System at Scale | Content & Media | todo | Threading, voting, spam, hot content |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 66 | Recommendation System — Full Pipeline | AI/ML | todo | Candidate gen → ranking → serving | |
| 67 | LLM-Powered Chatbot at Scale | AI/ML | todo | Streaming tokens, session, cost control | |
| 68 | RAG System over Enterprise Documents | AI/ML | todo | Chunking, embeddings, retrieval, grounding | |
| 69 | A/B Testing & Experimentation Platform | AI/ML | todo | Assignment, metrics, stat significance | |
| 70 | Feature Store for ML | AI/ML | todo | Online vs offline, point-in-time correctness | |
| 71 | ML Model Serving Infrastructure | AI/ML | todo | Shadow mode, canary, latency SLO | |
| 72 | Vector Database & Semantic Search | AI/ML | todo | HNSW, ANN, embedding freshness |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 73 | Search Engine Internals (Elasticsearch) | Data & Storage | todo | Inverted index, relevance scoring | |
| 74 | Time-Series Database | Data & Storage | todo | InfluxDB, downsampling, retention | |
| 75 | Graph Database & Social Network Queries | Data & Storage | todo | Neo4j, shortest path, friend-of-friend | |
| 76 | Data Warehouse & Lakehouse Architecture | Data & Storage | todo | Iceberg, Parquet, partitioning | |
| 77 | Change Data Capture (CDC) | Data & Storage | todo | Debezium, Binlog tailing, event propagation | |
| 78 | Consistent Hashing Deep Dive | Data & Storage | todo | Virtual nodes, hot spots, rebalancing | |
| 79 | Bloom Filter & Probabilistic Data Structures | Data & Storage | todo | HyperLogLog, Count-Min Sketch | |
| 80 | LRU / LFU Cache Implementation | Data & Storage | todo | LinkedHashMap, Caffeine, eviction |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 81 | Distributed Tracing System | Reliability | todo | OpenTelemetry, sampling, tail-based | |
| 82 | Circuit Breaker & Bulkhead Patterns | Reliability | todo | Resilience4j, half-open, fallback | |
| 83 | Disaster Recovery — RTO / RPO Planning | Reliability | todo | Backup strategies, failover runbook | |
| 84 | Chaos Engineering Framework | Reliability | todo | Steady state, blast radius, game days | |
| 85 | Zero-Downtime Deployments & Schema Migrations | Reliability | todo | Blue-green, expand-contract, canary | |
| 86 | Distributed Lock Service | Reliability | todo | Redlock, fencing tokens, ZooKeeper | |
| 87 | Leader Election & Consensus (Raft / Paxos) | Reliability | todo | Split-brain, quorum, term numbers | |
| 88 | Multi-Region Active-Active Design | Reliability | todo | Conflict resolution, CRDT, global LB |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 89 | Identity & Access Management (IAM) | Security | todo | RBAC vs ABAC, policy engine | |
| 90 | OAuth2 & OpenID Connect Deep Dive | Security | todo | Token lifecycle, PKCE, refresh rotation | |
| 91 | Zero-Trust Network Architecture | Security | todo | mTLS, BeyondCorp, SPIFFE/SPIRE | |
| 92 | Audit Logging & Compliance Trail | Security | todo | Immutable log, SOC2, GDPR | |
| 93 | GDPR Right-to-Erasure Implementation | Security | todo | Crypto-shredding, propagation | |
| 94 | Data Masking & Tokenisation Service | Security | todo | PCI DSS, PII vault | |
| 95 | Healthcare — Patient Record System (EHR) | Compliance | todo | HIPAA, consent management |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 96 | Event Sourcing + CQRS | Architecture | todo | Append-only log, projection rebuild | |
| 97 | Saga Pattern (Distributed Transactions) | Architecture | todo | Choreography vs orchestration | |
| 98 | Strangler Fig & Anti-Corruption Layer | Architecture | todo | Monolith migration, domain boundary | |
| 99 | Multi-Tenant SaaS Platform Architecture | Architecture | todo | Isolation models, noisy neighbour | |
| 100 | Outbox Pattern + Transactional Messaging | Architecture | todo | At-least-once, idempotent consumers |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 101 | Virtual Threads vs Reactive (Loom vs WebFlux) | Java Deep Dive | todo | Java 21, I/O bound, thread-per-request | |
| 102 | JVM GC Tuning for Production | Java Deep Dive | todo | G1 vs ZGC vs Shenandoah, Generational ZGC | |
| 103 | Spring Boot 3 + GraalVM Native Image | Java Deep Dive | todo | AOT, reflection hints, startup time | |
| 104 | Structured Concurrency (Java 21) | Java Deep Dive | todo | StructuredTaskScope, cancellation | |
| 105 | CompletableFuture Pitfalls in Production | Java Deep Dive | todo | Error propagation, thread pool starvation | |
| 106 | Domain-Driven Design with Records & Sealed Classes | Java Deep Dive | todo | Value objects, aggregates, exhaustive switch | |
| 107 | Database Connection Pool Tuning (HikariCP) | Java Deep Dive | todo | Pool sizing formula, leak detection | |
| 108 | Reactive Streams & Backpressure (Project Reactor) | Java Deep Dive | todo | Flux, Mono, scheduler selection |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 109 | Ride-Hailing Pricing Engine (Surge) | Geospatial | todo | Real-time demand model, elasticity | |
| 110 | Location Tracking & Geo-Fencing Service | Geospatial | todo | Moving objects, polygon queries, alerts | |
| 111 | Food Delivery Dispatch System | Geospatial | todo | Assignment optimisation, ETA, batching |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 112 | High-Frequency Trading Infrastructure | High Performance | todo | Kernel bypass, co-location, FPGA | |
| 113 | Video Conferencing (WebRTC Infrastructure) | High Performance | todo | SFU vs MCU, TURN/STUN, jitter buffer | |
| 114 | IOT Device Management Platform | High Performance | todo | MQTT, device shadow, OTA updates | |
| 115 | Service Mesh + Observability (Istio / Envoy) | High Performance | todo | mTLS, traffic policy, telemetry |
| # | Topic | Category | Status | Published URL | Notes |
|---|---|---|---|---|---|
| 116 | Internal Developer Platform (IDP) | Architecture | todo | Golden paths, self-service, paved road | |
| 117 | Cost Optimisation Framework (FinOps) | Architecture | todo | Right-sizing, spot strategy, waste | |
| 118 | gRPC vs REST vs GraphQL — Protocol Trade-offs | Architecture | todo | When to pick which, streaming, contracts | |
| 119 | Event-Driven Architecture Deep Dive | Architecture | todo | Domain events, eventual consistency | |
| 120 | Ad Click Aggregation & Attribution System | Scalability | todo | Lambda arch, exactly-once, privacy |
- Total topics: 120
- Published: 0 (0%)
- In progress: 0
- Todo: 120
Last updated: 2026-04-18
| Category | Count |
|---|---|
| Classic “Design X” | 20 |
| Fintech | 11 |
| E-Commerce & Marketplace | 9 |
| Booking & Reservation | 5 |
| Real-Time & Streaming | 6 |
| Infra & Developer Tools | 8 |
| Content & Media | 6 |
| AI / ML Systems | 7 |
| Data & Storage | 8 |
| Reliability & Operations | 8 |
| Security & Compliance | 7 |
| Architecture Patterns | 5 |
| Java Deep Dives | 8 |
| Geospatial & Location | 3 |
| High Performance | 4 |
| Platform & FinOps | 5 |
| Total | 120 |
Weeks 1–4 (Foundation): #1–20 — Classic questions. Build the pattern muscle.
Weeks 5–8 (Fintech focus): #21–31 — Moniepoint-relevant depth.
Weeks 9–12 (E-Commerce + Booking): #32–45 — Transactional systems, contention.
Weeks 13–16 (Real-Time + Infra): #46–59 — Operational maturity signals.
Weeks 17–20 (Content + AI/ML): #60–72 — Modern system design vocabulary.
Weeks 21–24 (Data + Reliability): #73–88 — Senior/staff-level depth.
Weeks 25–28 (Security + Arch + Java): #89–120 — EM/architect differentiation.
At 1 topic / weekday: ~24 weeks to full coverage. At 1 topic / day: 4 months.