Distributed Systems Design — case syllabus

The 44-case applied layer of this track. The 19 foundation lessons derive the patterns; these case drills are where you apply them under realistic prompts. This page maps the 44 drills to their sources — the Alex Xu books and archive — and shows the coverage without duplicating the source material.

How to use the cases

Work the 19 foundation lessons first — they build the vocabulary (partitioning, replication, consistency, queues, fault tolerance) that every case below assumes. Then treat each case as a drill: state the requirements and estimates, reach for the foundation patterns by name, and defend the trade. The cases are the second half of the track, not an optional appendix.

Source Coverage

Source	Role in the site	What it contributes
System Design Interview, Vol. 1	Classic interview spine	Scaling, estimation, interview method, then core cases: rate limiter, consistent hashing, key-value store, IDs, short links, crawler, notifications, feed, chat, autocomplete, video, and file storage.
System Design Interview, Vol. 2	Advanced case-study layer	Location, maps, queues, observability, ad aggregation, reservations, email, object storage, leaderboards, payments, wallets, and stock exchange.
System Design Big Archive	Primer and gap filler	Short topics around databases, security, web/networking, cloud, caching, messaging, storage, operations, payments, geo, collaboration, and flash sales.

The Existing Foundation Track

These pages are already the right prerequisite path. They should remain the main sequence because they teach the forces behind the cases.

Method, estimates, and requirements

The interview script, back-of-envelope math, and the habit of letting numbers choose architecture.

Covers Vol. 1 Ch. 1-3 plus archive estimation/scaling topics.

Contract and data layer

API style, data modeling, storage engines, indexes, database choice, and the costs of each access pattern.

Covers archive API, database, isolation, and storage primers.

Scale the stateless tier

Load balancing, stateless replicas, caching, API edge concerns, CDNs, and rate limiting as protection.

Covers Vol. 1 scaling/rate limiter material and archive cache/CDN topics.

Scale state

Partitioning, replication, consistency, consensus, transactions, idempotency, and fault tolerance.

Covers the distributed-systems concepts used by almost every case.

Operate and synthesize

Optimization, observability, service decomposition, archetypes, and the capstone interview walkthrough.

Covers archive operations, deployment, outage, and monitoring topics.

Case-Study Lessons

Each case page is original and uses the same rubric: requirements, estimates, API/data model, linearized design, deep dives, failures, and trade-offs. The source column is a coverage pointer, not a prescription to copy.

Phase 1 - Core distributed building blocks

No.	Lesson	Source	Design focus
C01	Design a rate limiter	Vol. 1 Ch. 4	Token bucket, sliding windows, shared counters, edge placement, abuse protection.
C02	Design consistent hashing	Vol. 1 Ch. 5	Rings, virtual nodes, remapping cost, hot shards, cache/database ownership.
C03	Design a key-value store	Vol. 1 Ch. 6	Partitioning, replication, quorum reads/writes, compaction, failure recovery.
C04	Design a distributed unique ID generator	Vol. 1 Ch. 7, archive	Snowflake-style IDs, monotonicity, clock skew, region bits, collision budgets.
C05	Design a URL shortener	Vol. 1 Ch. 8	Read-heavy routing, ID allocation, redirects, analytics, abuse, cache hit rate.

Phase 2 - Search, feeds, communication, and collaboration

No.	Lesson	Source	Design focus
C06	Design a web crawler	Vol. 1 Ch. 9, archive	Frontier scheduling, politeness, duplicate detection, robots rules, content storage.
C07	Design a notification system	Vol. 1 Ch. 10, archive	Fanout, device tokens, templates, preferences, retry, dedupe, channel priority.
C08	Design a news feed	Vol. 1 Ch. 11	Fanout-on-write vs fanout-on-read, celebrity users, ranking, freshness, storage.
C09	Design a chat system	Vol. 1 Ch. 12	WebSockets, message ordering, online presence, offline sync, multi-device state.
C10	Design search autocomplete	Vol. 1 Ch. 13	Trie/FST style serving, prefix aggregation, personalization, updates, latency.
C11	Design Twitter-style timelines	Archive	Hybrid fanout, social graph reads, ranking, backfill, cache invalidation.
C12	Design Google Docs-style collaboration	Archive	Operational transform/CRDT choices, presence, conflict handling, document storage.
C13	Design Gmail or a distributed email service	Vol. 2 Ch. 8, archive	SMTP flow, inbox indexing, spam pipeline, delivery retry, search and attachments.

Phase 3 - Media and storage products

No.	Lesson	Source	Design focus
C14	Design YouTube	Vol. 1 Ch. 14	Upload, transcoding, metadata, CDN, recommendations boundary, hot video traffic.
C15	Design Google Drive	Vol. 1 Ch. 15	Large file upload, chunking, sync, metadata, conflict resolution, sharing.
C16	Design S3-like object storage	Vol. 2 Ch. 9, archive	Object metadata, placement, replication, erasure coding, durability math.
C17	Design large file upload and serving	Archive	Multipart upload, resumability, checksums, CDN, object lifecycle policy.
C18	Block, file, and object storage primer	Archive	Storage interface trade-offs and how they drive product design choices.

Phase 4 - Geo, maps, and realtime location

No.	Lesson	Source	Design focus
C19	Design a proximity service	Vol. 2 Ch. 1, archive	Geohash, quadtrees, nearby search, cache by cell, privacy and freshness.
C20	Design nearby friends	Vol. 2 Ch. 2	Location streams, pub/sub, friend graph filtering, online state, battery trade-offs.
C21	Design Google Maps	Vol. 2 Ch. 3, archive	Map tiles, routing, traffic updates, storage, rendering, offline/cache behavior.
C22	Geospatial indexes and quadtrees	Archive	Grid, geohash, quadtree, S2-style cells, precision vs fanout.

Phase 5 - Data infrastructure and observability

No.	Lesson	Source	Design focus
C23	Design a distributed message queue	Vol. 2 Ch. 4, archive	Topics, partitions, consumer groups, ordering, durability, backpressure.
C24	Design metrics monitoring and alerting	Vol. 2 Ch. 5, archive	Ingestion, time-series storage, rollups, alert evaluation, cardinality control.
C25	Design ad click event aggregation	Vol. 2 Ch. 6	Event pipelines, dedupe, late data, batch vs stream, exactly-once illusions.
C26	Why Kafka is fast and when to use it	Archive	Append logs, batching, zero-copy, page cache, partition parallelism.
C27	At-most, at-least, and effectively-once delivery	Archive	Idempotency, transactions, outbox, consumer offsets, replay strategy.
C28	Debugging CPU, memory, and IO incidents	Archive	Symptom-first diagnosis, telemetry, saturation, deployment rollback.

Phase 6 - Marketplaces, reservations, and burst traffic

No.	Lesson	Source	Design focus
C29	Design a hotel reservation system	Vol. 2 Ch. 7, archive	Inventory, booking holds, overbooking, payment handoff, consistency boundaries.
C30	Design a flash sale system	Archive	Queue gating, stock counters, fairness, cache pre-warm, overload control.
C31	Design a realtime gaming leaderboard	Vol. 2 Ch. 10	Sorted sets, partitioning, top-k, season resets, cheat/fraud hooks.

Phase 7 - Payments, wallets, and financial systems

No.	Lesson	Source	Design focus
C32	Design a payment system	Vol. 2 Ch. 11, archive	Payment intent, ledger, idempotency, retry, PSP integration, reconciliation.
C33	Design a digital wallet	Vol. 2 Ch. 12	Ledger model, balance reads, double-entry accounting, holds, auditability.
C34	Money movement and reconciliation	Archive	Settlement, posting, mismatch detection, retry, compensating correction.
C35	Avoid double charges	Archive	Idempotency keys, outbox, state machine, duplicate webhook handling.
C36	Payment security, SWIFT, and foreign exchange	Archive	Threat model, rails, FX quote lifecycle, compliance and audit constraints.

Phase 8 - Trading systems

No.	Lesson	Source	Design focus
C37	Design a stock exchange	Vol. 2 Ch. 13, archive	Order book, matching engine, sequencing, market data, persistence, risk checks.
C38	Microsecond-latency exchange architecture	Archive	Latency budget, colocated components, single-writer design, recovery logs.
C39	Match buy and sell orders	Archive	Price-time priority, order types, deterministic replay, correctness before scale.

Phase 9 - Web, security, and cloud primers

No.	Lesson	Source	Design focus
C40	Secure API access, SSO, passwords, and HTTPS	Archive	Authn/authz, OAuth/OIDC shape, password hashing, TLS termination, API signing.
C41	DNS, HTTP, browser request lifecycle, and QUIC	Archive	Name resolution, connection setup, protocol evolution, page-load bottlenecks.
C42	Microservices, containers, deployment, and Lambda	Archive	Runtime boundaries, rollout strategy, serverless execution, operational trade-offs.
C43	IaaS, PaaS, SaaS, and cloud choice	Archive	Responsibility boundaries, managed services, lock-in, cost and control.
C44	Design an AI coding engine	Archive	Bridge to ML system design: retrieval, sandboxing, tool calls, evaluation, serving.

Publishing Order

Wave	Ship first	Why
1	C01-C05	These are reusable primitives that appear inside many later cases.
2	C06-C18	Classic social, search, communication, media, and storage prompts. They make the track immediately useful for interviews.
3	C19-C28	Advanced distributed dataflow: geo, queues, metrics, aggregation, and operations.
4	C29-C39	High-correctness domains: reservations, payments, wallets, and trading.
5	C40-C44	Primer lessons that fill conceptual gaps and cross-link to security, cloud, and ML systems.

Content rule

The lessons should not be book notes. Use the PDFs to choose coverage, then write each lesson as an original design exercise with calculations, trade-offs, failure modes, and links back to the 19 foundation lessons.