Taught, not listed
Full explanations, analogies, and worked reasoning for every topic.
15 modules · 75 lessons · 10 worked case studies · zero fluff
Learn system design the way it actually works.
Not a list of buzzwords. Every concept — from requirements to consistent hashing — is taught with a plain-English explanation, a diagram you can redraw on a whiteboard, the trade-offs that matter, and the mistakes that sink interviews. Read it like a book, or jump straight to the topic you need.
Diagram-first
Each lesson ships with a clean, redrawable architecture diagram.
Trade-offs & pitfalls
Where each approach breaks, and how a senior engineer answers.
12modules
60+illustrated lessons
60+diagrams
10worked case studies
The course
Read it front to back, or dive into any topic.
Pick a module on the left and open any lesson. Each one is a complete, self-contained explanation with a diagram. Your progress is saved in this browser automatically.
Foundations
Lesson
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Interview command center
Answer with senior structure, not random buzzwords.
Use this operating system in every round: clarify scope, set SLOs, propose architecture, expose trade-offs, and close with failure handling and evolution.
8-step whiteboard flow
- Clarify product scope, users, and non-goals.
- Set scale assumptions and concrete SLOs.
- Define core APIs and data entities.
- Draw baseline architecture for the happy path.
- Bottleneck hunt: latency, throughput, and hotspots.
- Add scale tools: cache, queue, partition, replication.
- Cover failure, consistency, and disaster recovery.
- Close with observability, cost, and rollout plan.
Trade-off matrix interviewers love
- Latency vs consistency: strict reads for money; eventual for feeds.
- Availability vs correctness: fail open only for non-critical flows.
- Write cost vs durability: quorum writes for irreversible events.
- Simplicity vs flexibility: default to fewer moving parts first.
- Cost vs reliability: map each extra nine to business impact.
Red flags to avoid in rounds
- Starting with Kafka, Redis, and sharding before requirements.
- Giving average latency while ignoring p95/p99.
- Saying “highly available” without an explicit SLO.
- No story for idempotency, retries, or backpressure.
- No visibility plan: metrics, logs, traces, alert ownership.
Senior answer template
Use this verbal framing to sound structured and calm under pressure:
"I will solve this in four passes: scope and SLOs, baseline architecture, scale and failure hardening, then operational readiness and cost. I will call out assumptions and trade-offs at each pass."
This single opener instantly improves interviewer confidence in your process.
60-second drills
Practice requirement extraction, API sketching, and SLO framing in timed bursts.
10-minute deep dives
Take one subsystem and defend consistency, durability, and scaling choices.
45-minute full simulations
Run the full loop end to end with clear assumptions and trade-off language.
Capstone practice
Premium capstone tracks for interview mastery.
Design these end to end, then evaluate yourself with explicit scoring: requirements clarity, architecture quality, failure depth, and trade-off reasoning.
URL shortener
Key generation, redirect latency, analytics pipeline, abuse controls, and durability.
Fraud detection
Streaming ingestion, feature stores, low-latency scoring, replayability, and model safety.
Authentication system
Token lifecycle, revocation, session consistency, rate limiting, and auditability.
Monitoring platform
Metric ingestion, time-series storage, alert reliability, and dashboard query speed.
Global chat platform
WebSocket fanout, delivery guarantees, presence, unread counters, and multi-region routing.
Ride-matching engine
Geo-indexing, dispatch fairness, surge pricing events, and failover during city spikes.
Video streaming service
Upload pipeline, transcoding queues, CDN edge caching, and personalized recommendation feeds.
Event ticketing system
Hot partition prevention, seat reservation consistency, payment idempotency, and anti-bot defense.
Self-evaluation scorecard (0-4 each)
Requirements: did you scope clearly with explicit non-goals?
Scale: were throughput, storage growth, and peak factors quantified?
Architecture: is the baseline simple and logically complete?
Trade-offs: did you justify alternatives and reject options on purpose?
Reliability: did you cover retries, idempotency, and recovery paths?
Operations: did you include observability, rollout, and cost?