Week 1 · The 6 Core Trade-offs & Estimation
Jun 2 to Jun 7
S1 · The 6 Core Trade-offs
The reusable axes every architecture decision moves along. Wed 6/3, 90 min.
/senior-to-staff/s01-core-tradeoffsS2 · Capacity Estimation & Requirements
Back-of-envelope math that bounds a design before you draw it. Fri 6/5, 90 min.
/senior-to-staff/s02-capacity-estimation cheat sheet Reference · cheat sheetSystem Design Estimation Cheat Sheet
The numbers, formulas, per-tool scaling thresholds, and 9 worked problems for interviews. Skim before any design round.
/cheatsheets/estimation 1-page brief Project 1 · due Jun 12P1 · Capacity Estimation Worksheet
Size one system in numbers and name the figure that decides its shape. One page.
/senior-to-staff/p1-capacity-worksheetWeek 2 · Data Stores & Data at Scale
Jun 8 to Jun 14
S3 · Relational vs Document vs Key-Value
Picking a store from access patterns, not familiarity. Wed 6/10, 90 min.
/senior-to-staff/s03-data-stores cheat sheet Reference · cheat sheetData Stores Cheat Sheet
The four questions, six families side by side, a card per database (Postgres, Mongo, Redis, Cassandra, …), ERD design and normal forms. Companion to S3.
/cheatsheets/data-storesS4 · Data at Scale: Sharding, Replication, Caching
What changes when one node stops being enough. Fri 6/12, 90 min.
/senior-to-staff/s04-data-at-scale cheat sheet Reference · cheat sheetData at Scale Cheat Sheet
How to scale each database (Postgres, MySQL, Mongo, Redis, Cassandra, DynamoDB, …) for reads vs writes, the lever you pull, and the trade-off. Sharding, replication and caching side by side. Companion to S4.
/cheatsheets/data-at-scale cheat sheet Reference · cheat sheetPostgreSQL vs MongoDB Cheat Sheet
SQL vs NoSQL side by side: the two data shapes, how each handles ACID, what only one can do, when to choose which, and interview questions with answers. Companion to S4.
/cheatsheets/postgres-vs-mongodb cheat sheet Reference · cheat sheetCaching Strategies Cheat Sheet
The first lever for scaling reads, in full: the hit-ratio math, read strategies (cache-aside vs read-through) and write strategies (write-through, write-back, write-around) with sequence diagrams, how they pair, consistency and the stale window, eviction (LRU/LFU/TTL), invalidation and the delete-vs-update trap, the failure modes (stampede, hot key, penetration, avalanche) and their fixes, the layers from browser to CDN to Redis, CDN delivery, which technology to use (Redis vs Memcached and friends), cache architecture and topology (local vs distributed vs near-cache, sharding, consistent hashing), key design and metrics, with a decision tree and interview Q&A. Companion to S4.
/cheatsheets/caching-strategies 1-page brief Project 2 · due Jun 19P2 · ADR #1: Database Decision
Record a data-store choice as a one-page ADR, with the trade-off named.
/senior-to-staff/p2-adr-databaseWeek 3 · APIs & Distributed Systems
Jun 15 to Jun 21
S5 · API Design & Networking Fundamentals
Contracts, versioning, and the network you can't ignore. Wed 6/17, 90 min.
/senior-to-staff/s05-api-design cheat sheet Reference · cheat sheetAPI Design & Networking Cheat Sheet
The contract and the network on one page: REST vs gRPC vs GraphQL and when to choose which, contract design (idempotency, pagination, versioning, status codes and error shapes, rate limiting), HTTP/1.1 vs 2 vs 3, the DNS/TCP/TLS handshakes, keep-alive and connection pooling, L4 vs L7 load balancing and the CDN edge, a decision table and interview Q&A. Companion to S5.
/cheatsheets/api-design cheat sheet Reference · cheat sheetSecurity & Auth Cheat Sheet
Everything security and identity on one page, with the flows drawn out. Authn vs authz; how identity is carried (sessions, JWTs, opaque tokens); OAuth 2.1 authorization-code + PKCE, OpenID Connect, SAML SSO and federation, passkeys/WebAuthn, the BFF token-handler pattern, service-to-service mTLS + SPIFFE + token exchange (RFC 8693); where to enforce auth; the authorization models (RBAC, ABAC, ReBAC/Zanzibar); plus password storage (argon2 + salt), encryption in transit and at rest, and the common web attacks (injection, XSS, CSRF, SSRF, IDOR) and their defenses. Decision guide and interview Q&A. Companion to S5.
/cheatsheets/security-authS6 · Distributed Systems Patterns
Consensus, idempotency, sagas, and the failures behind them. Fri 6/19, 90 min.
/senior-to-staff/s06-distributed-patterns cheat sheet Reference · cheat sheetBackend Clocks & Time Cheat Sheet
The "no global clock" problem unpacked for backend engineers and interviews: physical sync (NTP, PTP), wall vs monotonic (with code), logical clocks (Lamport, vector), hybrids (HLC, TrueTime), time-based IDs (Snowflake, ULID, UUIDv7), backend rules (UTC, JWT skew, fencing tokens), a decision tree, and interview Q&A. Companion to S6.
/cheatsheets/clocks-and-time cheat sheet Reference · cheat sheetConsistency & Consensus Cheat Sheet
How distributed systems agree and what it costs: CAP and PACELC, the consistency spectrum (linearizable to eventual), quorums (W+R>N), replication topologies, consensus with Raft and majorities, and cross-service transactions (2PC vs saga), with a decision table and interview Q&A. Companion to S6.
/cheatsheets/consistency-consensusWeek 4 · Architectural Styles & DDD
Jun 22 to Jun 28
S7 · Architectural Styles: Monolith to Microservices
The spectrum, and when each point on it is the right call. Wed 6/24, 90 min.
/senior-to-staff/s07-architectural-styles cheat sheet Reference · cheat sheetKafka vs RabbitMQ Cheat Sheet
Messaging for interviews: the log-vs-broker distinction, core concepts for each (partitions, consumer groups, offsets vs exchanges, queues, bindings, acks), delivery semantics, ordering, when to use which, common patterns, and interview Q&A. Companion to S6 and S7.
/cheatsheets/kafka-vs-rabbitmqS8 · Domain-Driven Design for Architects
Bounded contexts and service boundaries that don't leak. Fri 6/26, 90 min.
/senior-to-staff/s08-ddd 1-page brief Project 3 · due Jul 3P3 · ADR #2: Service Boundary Decision
Decide where one service boundary goes, justified by a real seam, not the org chart.
/senior-to-staff/p3-adr-service-boundary cheat sheet Reference · cheat sheetEvent Storming for Food Delivery System
A full event-storming session on a real project (a food-delivery platform), with the sticky-note board growing as you scroll: chaotic events, the timeline, hotspots and pivotal events, actors and external systems, commands, aggregates, policies, read models, until the bounded contexts emerge and become services. Companion to S8.
/system-designs/event-storming-food-delivery-system case study Case study · real appEvent Storming, for Club Control Panel
ClubCP, a real club-management system, taken through a full event-storming session, the same steps, real answers: every sticky traced from the actual code as the board grows down the page. The timeline of a member attending a paid event, the real hotspots (dual payment providers, idempotent capture, capacity & waitlist, no-show emails, bounce suppression), then actors, commands, aggregates, policies and read models, until ClubCP's bounded contexts emerge. The whole workshop on real stakes.
/system-designs/event-storming-club-control-panelWeek 5 · Reliability & Operability
Jun 29 to Jul 5
S9 · Designing for Failure
Blast radius, fail-open vs fail-closed, graceful degradation. Wed 7/1, 90 min.
/senior-to-staff/s09-designing-for-failure cheat sheet Reference · cheat sheetResilience Patterns Cheat Sheet
The whole failure-handling toolkit on one page: the four bounding patterns (timeout, retry with backoff and jitter, circuit breaker, bulkhead), fallback and graceful degradation, load shedding, correctness under retry (idempotency, at-least-once vs exactly-once, dead-letter queues), fail-open vs fail-closed per path, operational glue, a symptom-to-pattern decision table, and interview Q&A. Companion to S9.
/cheatsheets/resilienceS10 · Observability & Operational Readiness
SLIs/SLOs, the three pillars, and what "ready to run" means. Fri 7/3, 90 min.
/senior-to-staff/s10-observability cheat sheet Reference · cheat sheetObservability & SLO Cheat Sheet
Reliability as a number on one page: SLI / SLO / error budget (with what each nine buys in minutes), the three pillars (metrics, logs, traces) and their pitfalls, the RED and USE methods, symptom and burn-rate alerting, an operational-readiness checklist, a question-to-pillar decision table, and interview Q&A. Companion to S10.
/cheatsheets/observability 1-page brief Project 4 · due Jul 6P4 · ADR #3: Capstone Decision
Your hardest call, reasoned end to end: number, trade-off, failure, operability.
/senior-to-staff/p4-adr-capstone 1-page brief Project 5 · due Jul 6P5 · System Design Document
The whole capstone system on a few pages. The artifact that most looks like the job.
/senior-to-staff/p5-design-docWeek 6 · Design Review
Jul 6 to Jul 9
S11 · Live Group Design Session
Designing together under pushback. Tue 7/7, 60 min.
/senior-to-staff/s11-group-designS12 · Design Review Presentations
Present, defend, and read the room. Thu 7/9, 90 min.
/senior-to-staff/s12-design-review 1-page brief Project 6 · capstoneP6 · Design Review Presentation
Present and defend your design live. Rehearsed in S11, presented Thu 7/9.
/senior-to-staff/p6-design-review worked design Reference · worked system designDesign Twitter / X: the home timeline
The classic prompt, worked end to end with the course method: requirements, estimation, API, data model, a high-level architecture diagram, the fan-out deep dives (write vs read, the celebrity hot-key problem, ranking), reliability (S9) and observability (S10), and the trade-offs along the six core axes. Applies the whole course to one interview question.
/system-designs/twitter worked design Reference · worked system designDesign WhatsApp: chat & messaging
Realtime messaging worked end to end: requirements, estimation (connections as the deciding number), the persistent-socket protocol, data model, a high-level architecture diagram, the deep dives (holding hundreds of millions of connections, delivery and ordering semantics, store-and-forward for offline), reliability (S9) and observability (S10), and the trade-offs along the six core axes.
/system-designs/whatsapp worked design Reference · worked system designDesign Stripe: payments
The correctness-first design, worked end to end: requirements, estimation (why QPS is not the constraint), the idempotent API, data model, a high-level architecture diagram, the deep dives (idempotency keys, a double-entry ledger and exactly-once accounting, reconciliation and fail-closed by default), reliability (S9) and observability (S10), and the trade-offs along the six core axes. The deliberate counterpoint to Twitter and WhatsApp.
/system-designs/stripeMore worked system designs
Reference · the method, then the classic interview prompts worked end to end
The System Design Interview Framework
The whole method on one page: how to run the hour and the seven steps (requirements and scope, estimation, API, data and stores, high-level design, deep dives, trade-offs), plus what actually scores, time budgets, and the common traps. The umbrella the eight worked designs below all apply. Bring it to any "design X" prompt.
/system-designs/framework worked design Reference · worked system designDesign Uber: ride-sharing
The geospatial design, worked end to end: requirements, estimation (a million location writes per second as the deciding number), API, data model, a high-level architecture diagram, the deep dives (geospatial indexing with cells / geohash / S2 / H3, the real-time location firehose, matching and dispatch without double-booking), reliability (S9) and observability (S10), and the trade-offs along the six core axes.
/system-designs/uber worked design Reference · worked system designDesign YouTube: video streaming
The video design, worked end to end: requirements, estimation (egress bandwidth as the deciding constraint), API, data model, a high-level architecture diagram, the deep dives (the async upload + transcode pipeline and rendition ladder, CDN delivery with adaptive bitrate, and read scale across the long tail), reliability (S9) and observability (S10, rebuffer ratio), and the trade-offs along the six core axes.
/system-designs/youtube worked design Reference · worked system designDesign Dropbox: file sync
The file-sync design, worked end to end: requirements, estimation (edit-size to file-size as the deciding ratio), a content-addressed chunk API, data model, a high-level architecture diagram, the deep dives (content-defined chunking and dedup, the cursor-based sync protocol, and conflict resolution via conflicted copies), reliability (S9) and observability (S10, dedup ratio), and the trade-offs along the six core axes.
/system-designs/dropbox worked design Reference · worked system designDesign Google Search: web search
The search design, worked end to end: requirements, estimation (the index does not fit on one machine, so scatter-gather), API, data model, a high-level architecture diagram, the deep dives (the crawler frontier, the inverted index with document-partitioned scatter-gather, two-phase ranking and typeahead), reliability (S9, drop slow shards on a deadline) and observability (S10, latency + completeness), and the trade-offs along the six core axes.
/system-designs/google-search worked design Reference · worked system designDesign Ticketmaster: event ticketing
The high-contention design, worked end to end: requirements, estimation (buyers-to-seats ratio at onsale as the deciding number), a hold-then-purchase API, data model, a high-level architecture diagram, the deep dives (high-contention inventory with no double-booking via an atomic conditional update, the onsale spike and virtual waiting room, seat holds and expiry without a race), reliability (S9, fail closed on the seat) and observability (S10, double-booked = 0), and the trade-offs along the six core axes.
/system-designs/ticketmaster