◆ System Design · Zero→Hero
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Backend / Infra track · 17 × 30-min units

The System Design Interview,
built one 30-minute block at a time.

An interactive crash course that takes you from "I know the basics" to confidently driving a backend system design interview. Every unit is a self-contained 30-minute lesson with diagrams, tradeoff drills, a calculator or two, and a quiz. Work top to bottom, or jump to a weak spot.

~8.5 hrs total backend / infra-heavy assumes some CS background progress saved in your browser installable · works offline
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How to use this course Each unit is scoped to a real 30-minute sitting. Read the objectives, work through the explanations, actually click the quizzes and calculators (retrieval practice is what makes it stick), then hit Mark complete at the bottom. Two units a day → interview-ready in about two weeks. Arrow keys ← → move between lessons.

Module 0 · Foundations 60 min

01
The Interview Playbook
The 7-step framework for driving any design interview — and how you're actually scored.
30m
02
Back-of-the-Envelope Estimation
QPS, storage for 1 day vs 10 years, bandwidth, memory — with a live capacity calculator.
30m

Module 1 · The Data Layer 120 min

03
Databases I — SQL vs NoSQL & Schema Design
Relational vs non-relational, picking a store, and modeling your data.
30m
04
Databases II — Sharding, Replication & Redundancy
Partitioning strategies, primary/replica, proxies, and the failure modes.
30m
05
CAP, Consistency & Availability
Available vs consistent, consistency models, and how to say the right words.
30m
06
Caching
memcached vs Redis, read/write patterns, invalidation, eviction, and the hard parts.
30m

Module 2 · Communication 60 min

07
API Design
REST vs GraphQL, idempotency, auth, pagination, and intra-service comms (gRPC).
30m
08
Message Queues & Async Processing
SQS vs Kafka vs Kinesis, when to queue, ordering, size limits, exception handling.
30m

Module 3 · Scale & Delivery 120 min

09
Scaling & Load Balancing
"Handle 5× traffic", read vs write optimization, horizontal vs vertical, LB algorithms.
30m
10
Content Distribution — CDN, DNS & DDoS
Edge caching, global distribution, DNS, and defending the front door.
30m
11
Object Storage & Media Pipelines
Storing images/audio/video, transcoding, compression, and serving at scale.
30m
12
Hosting — Containers & Kubernetes
Docker vs Kubernetes, what orchestration buys you, and how to talk deployment.
30m

Module 4 · Operate & Architect 90 min

13
Observability & Alerting
Metrics, logs, traces, the four golden signals, SLOs and good alerts.
30m
14
Service Architecture & Modularity
Monolith vs microservices, service boundaries, image serving, developer APIs.
30m
15
Feed Generation (Deep Dive)
The classic question: pull vs push fan-out, the celebrity problem, aggregation.
30m

Module 5 · Edges & Capstone 60 min

16
Security, Analytics & the Frontend Edge
AuthN/Z, ML for abuse, analytics pipelines — plus a fast pass on web clients, SSR & frameworks.
30m
17
Capstone — Mock Interview
Design a photo-sharing feed end to end, applying every unit under the clock.
30m
Covers your whole deep-dive list Every topic from your source list is here: capacity estimation, data storage, sharding/replication, CAP, caching, API design, message queues, scaling, distribution/CDN/DNS/DDoS, object storage & media, hosting, observability, service architecture, feed generation, security, analytics, and the web-client/framework topics (covered lightly, per the backend focus).