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Key Concepts

  • Networking Essentials for System Design: The networking that matters for system design interviews: OSI layers 4 and 7, TCP vs UDP, DNS resolution, HTTP/1.1 to HTTP/3, and WebSockets.
  • CAP Theorem: The core distributed-systems trade-off: when a network partition hits, you pick consistency or availability. What CP and AP mean, with real examples.
  • Consistent Hashing: The Scale-Out Algorithm: Why modulo hashing breaks at scale, how the hash ring fixes it, and how virtual nodes and replication make it the backbone of distributed data stores.
  • Caching: The System Design Guide: Where to cache (client, server, CDN, Redis), read and write strategies, eviction and invalidation, and failure modes like cache avalanche and hot keys.
  • Load Balancing: The System's Traffic Cop: A deep dive into load balancers: Layer 4 vs Layer 7, algorithms like round robin and least connections, sticky sessions, and health checks.
  • Bloom Filters: The Probabilistic Data Structure: How Bloom Filters let Cassandra and Chrome test set membership with tiny memory: internals, false positives, sizing, deletion, and alternatives.

Technology Deep Dives

  • Apache Kafka: The Distributed Event Streaming Platform: Apache Kafka is the distributed commit log behind most event-driven systems, log pipelines, and stream processing. This guide covers the model that makes it work (topics, partitions, offsets), how producers and consumers behave, consumer groups and rebalancing, replication and the ISR, retention and compaction, the three delivery guarantees, how it differs from a traditional message queue, scaling the cluster without breaking key ordering, capacity planning, a configuration reference, and the operational traps interviewers probe.
  • Redis: The In-Memory Data Structure Store: A deep dive into Redis. Understand in-memory storage, single-threaded architecture, clustering, and critical use cases like caching, rate limiting, and pub/sub.

Practice Questions

  • Design IoT Monitoring Platform: Design a real-time IoT monitoring platform that ingests temperature, humidity, and pressure readings from millions of sensors worldwide. Support real-time dashboards with 5-minute rolling averages, threshold-based alerting, anomaly detection, and querying up to 3 months of historical data with automatic downsampling for older ranges.
  • Design WhatsApp / Chat System: Design a real-time messaging platform like WhatsApp or Facebook Messenger. Handle 1:1 and group messaging, online presence, read receipts, media sharing, end-to-end encryption, and guaranteed message delivery for 2 billion users.
  • Design URL Shortener: Design a URL shortening service like Bitly or TinyURL. Handle billions of short links, high read throughput, custom aliases, analytics tracking, and link expiration at scale.
  • Design Notification System: Design a notification platform that delivers push notifications, emails, SMS, and in-app messages across multiple channels. Handle user preferences, templating, priority levels, throttling, and delivery tracking at the scale of billions of notifications per day.
  • Design YouTube / Video Streaming: Design a video sharing and streaming platform like YouTube. Handle video uploads, transcoding, adaptive bitrate streaming, recommendations, and content delivery at the scale of 500 hours of video uploaded per minute and 1 billion hours watched per day.
  • Design Uber / Ride Sharing: Design a ride-sharing platform like Uber or Lyft. Handle real-time driver location tracking, rider-driver matching, ETA computation, surge pricing, trip management, and payments at the scale of millions of concurrent rides.
  • Design Web Crawler: Design a web crawler that systematically downloads and indexes billions of web pages. Handle URL discovery, politeness policies, duplicate detection, distributed coordination, and content extraction at the scale of crawling the entire indexable web.
  • Design Rate Limiter: Design a distributed rate limiting service that protects APIs from abuse and overload. Support multiple algorithms (token bucket, sliding window), per-user and per-API limits, distributed counting across multiple data centers, and real-time configuration changes at the scale of millions of requests per second.
  • Design Payment System: Design a payment processing platform like Stripe or Razorpay. Handle payment initiation, authorization, capture, refunds, webhook notifications, and reconciliation at the scale of millions of transactions per day with zero tolerance for double charges or lost payments.
  • Design Dropbox / File Sync: Design a cloud file storage and synchronization service like Dropbox or Google Drive. Handle file uploads, chunked storage, real-time sync across devices, conflict resolution, sharing and permissions, and efficient bandwidth usage at the scale of billions of files and hundreds of millions of users.
  • Design Twitter (Full Scale): Design a global social media platform like Twitter. This covers high-volume ingestion, hybrid fan-out, real-time analytics, search indexing, and system reliability at the scale of 500 million tweets per day.
Best sellerInterview prep path·Updated May 2026

System
design,
interviewed.

A repeatable framework for breaking down vague, open-ended design questions, paired with the patterns and trade-offs the best interviewers expect you to defend.

Level
Beginner to Advanced
Study time
20h
Lessons
10
System map · what you'll draw10 lessons
twitter-feed.architecture
1.2M QPS
CLIENTEDGESERVICESSTORAGEmobilewebdnscdnapi-gatewayrate-limit · auth · routingauth-svc3 nodespost-svcwritesfeed-svchot read pathmedia-svcworkerspostgresrediskafkas3GET /feedorigin pullPOST /tweetfanoutcache hit 94%
Design a Twitter newsfeedPractice problem
Topicscachingload-balancingshardingcap-theoremmicroservicesand more
01 · Outcomes

By the end, you'll be able to defend any design.

Three capabilities the course is built around. Not topics, not bullet points. Things you can demonstrably do at the end that you could not before.

01Capability

Decompose vague prompts into tractable sub-problems.

A reusable framework: clarify, scope, list functional and non-functional requirements, define the API, then design. The shape of every senior interview.

Clarifying questions worth asking
QPS, storage and latency back-of-envelope
API contract before architecture
02Capability

Make trade-offs you can defend on the spot.

Consistency vs. availability. SQL vs. NoSQL. Caching vs. recomputation. Synchronous vs. event-driven. The shape of the answer interviewers actually grade.

CAP and PACELC, in plain English
Replication, sharding, partitioning
Pick the right cache pattern
03Capability

Design real systems end-to-end.

Walk into a design round with reusable templates for URL shorteners, feeds, chat, video, payments, and rate limiters. The questions companies actually ask.

Design problems, walked through
Microservices, events, queues
When not to over-engineer
02 · Syllabus

Four chapters.
One syllabus.

Read top to bottom or jump in mid-syllabus. Every concept page has a sketch-along diagram, and every practice question is graded with feedback.

  1. 1What is a System Design Interview?FREE
  2. 2How to Approach a System Design InterviewFREE
03 · Inside the practice

Not a video.
A mock interview, graded.

Each practice problem runs the same shape as a real interview: clarify, define, design, defend. Every step is graded with specific strengths and gaps.

  1. 01
    Stepwise prompts mimic the real flow
    Clarifying questions, functional and non-functional, API contract, data model, architecture. The way real loops unfold.
  2. 02
    Diagram canvas, scored alongside text
    Sketch services and edges. Each node and arrow is evaluated as part of your answer, not as an afterthought.
  3. 03
    Feedback in seconds, with reasoning
    Graded on accuracy, completeness, and clarity. You see exactly what a strong answer would have covered, not just a score.
buildtooffer / system-design / practice / rate-limiter
Q · 02 / 05
  1. ✓Clarifying Q's
  2. 2Functional req's
  3. 3Non-functional
  4. 4API contract
  5. 5Data model
Q2 · FUNCTIONAL
Core requirements for a distributed rate limiter?
1. Rate limit per API request
2. Configurable per user / API key
3. …
DIAGRAM · 3 NODESclientapi-gwredis
Get feedback
FEEDBACK · 1.4s
4.0
/ 10
NEEDS WORK
Solid start, missed the response contract.
Accuracy
5/10
Complete
3/10
Clarity
6/10
✓2 Strengths
Identified per-key configurability.
!2 Gaps
Missing 429 + rate-limit headers.
04 · By the numbers
21
Lessons
6
Core concepts
2
Key technologies
11
Practice problems
05 · Get the course

One pack.
Two courses.

System design and the database fundamentals it depends on, shipped together. The introduction stays free to preview either way.

RecommendedPack · 2 courses

System Design + Database

Master both ends of the stack interviewers care about: the course you are on, plus the database fundamentals every design problem rests on.

—/ year
Renews annually · cancel anytime
System Design Interview course
Database Fundamentals course
Graded practice problems
Live diagram canvas
Introduction free to preview
Updates as the field moves
UPI / Cards / Net Banking
06 · FAQ

Honest answers.

The things people ask before buying, answered straight.

I have already read Alex Xu or DesignGurus. What is different here?+

Those are libraries of finished designs. This is a course built around the act of designing: you defend trade-offs and get graded feedback on the problems. Reading versus doing.

Do I need the Database course too?+

Yes, that is why they are packed together. Every system design problem reduces to database trade-offs at some point: sharding, replication, consistency. You cannot separate them cleanly, so we do not.

How long does it take to finish?+

Around 20 hours of material. Most learners finish in four to six weeks at three to four hours a week. You can read top to bottom or jump in mid-syllabus.

Do I need a strong background to start?+

No. The introduction builds the framework from first principles, and the glossary defines every term before the harder chapters use it. A working dev background is enough.

How does access work?+

Access is an annual subscription that renews yearly. The introduction chapter stays free to preview, so you can try the framework before unlocking the rest.

07 · Start today

21 lessons
between you and your
offer letter.

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Browse the syllabus·See all courses