A Practical Guide from Fundamentals to Real-World Architectures

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The system design interview is where senior offers are won or lost.

In 45 to 60 minutes you are asked to design something real companies spend years building: a URL shortener, a chat service, a news feed, a ticketing platform that survives a million fans arriving at once. Nobody expects a finished design. Interviewers want to see how you think — how you clarify a vague problem, estimate scale with rough numbers, choose the right building blocks, and defend your trade-offs.

This book teaches you exactly that, step by step. You get a repeatable framework you can apply to any question, the building blocks and distributed-systems concepts behind every good answer, and complete worked designs — all grounded in one realistic running example: Crowdline, a live-events ticketing and fan platform with flash sales, payments, share links, notifications, fan chat, feeds, search, live streams, and nearby-venue search.

• 418 pages · 28 chapters + 4 appendices
• How interviews are scored, and a 7-step framework for any question
• Back-of-the-envelope estimation with the arithmetic shown
• Networking, load balancers, and API design: REST, gRPC, GraphQL, WebSockets
• Data stores, caching, replication, sharding, and consistent hashing
• Queues, event logs, stream processing, object storage, and CDNs
• Consistency, CAP and PACELC, consensus, unique IDs, sagas, and the outbox pattern
• Idempotency, retries, backpressure, autoscaling, and load shedding
• 10 complete designs: URL shortener, rate limiter, notifications, chat, news feed, search and typeahead, flash-sale ticket booking, payments ledger, video streaming, and proximity search
• SLOs, observability, security, multi-region architecture, and disaster recovery
• A full mock interview walkthrough, cheat sheet, templates, and checklist

Table Of Contents

Part I — Interview Foundations

• Ch 1 · How System Design Interviews Work and What Interviewers Look For
• Ch 2 · A Repeatable Framework: Requirements, Estimates, APIs, Data Model, High-Level Design, Deep Dives
• Ch 3 · Back-of-the-Envelope Estimation: Throughput, Storage, Bandwidth, and Latency
• Ch 4 · Networking Essentials: DNS, TCP/UDP, HTTP, TLS, Load Balancers, and Proxies
• Ch 5 · API Design for Interviews: REST, gRPC, GraphQL, WebSockets, and Webhooks

Part II — Core Building Blocks

• Ch 6 · Choosing Data Stores: Relational, Key-Value, Document, Wide-Column, Graph, and Search
• Ch 7 · Caching: Cache-Aside, Write-Through, Eviction, Invalidation, and Hot Keys
• Ch 8 · Replication, Partitioning, and Consistent Hashing
• Ch 9 · Message Queues, Event Logs, and Stream Processing
• Ch 10 · Object Storage, CDNs, and Media Pipelines

Part III — Distributed Systems Concepts

• Ch 11 · Consistency Models, CAP, and PACELC in Practice
• Ch 12 · Consensus, Leader Election, Coordination, and Unique ID Generation
• Ch 13 · Distributed Transactions: Two-Phase Commit, Sagas, and the Transactional Outbox
• Ch 14 · Idempotency, Retries, Deduplication, and "Exactly-Once" Semantics
• Ch 15 · Scalability Patterns: Stateless Services, Autoscaling, Backpressure, and Load Shedding

Part IV — Classic Interview Designs

• Ch 16 · Designing a URL Shortener: Crowdline Share Links
• Ch 17 · Designing a Distributed Rate Limiter
• Ch 18 · Designing a Notification System
• Ch 19 · Designing Chat and Presence: Crowdline Fan Rooms
• Ch 20 · Designing a News Feed: Artist Updates and Activity Timelines

Part V — Real-World Architectures

• Ch 21 · Designing Search, Typeahead, and Top-K Trending
• Ch 22 · Designing a Ticket Booking System for Flash-Sale Traffic
• Ch 23 · Designing a Payment System and Double-Entry Ledger
• Ch 24 · Designing Live and On-Demand Video Streaming
• Ch 25 · Designing Proximity Search: Nearby Venues and Events

Part VI — Operating at Scale and the Capstone

• Ch 26 · Reliability and Observability: SLOs, Monitoring, Tracing, and Incident Response
• Ch 27 · Security, Multi-Region Architecture, and Disaster Recovery
• Ch 28 · Capstone: Crowdline End to End — A Full Mock Interview Walkthrough

Appendices

• App A · System Design Cheat Sheet
• App B · Interview Templates and Reference Tables
• App C · Production Readiness Checklist
• App D · Glossary

WHO IT IS FOR
Software engineers preparing for system design interviews at mid-level, senior, and staff levels; backend and full-stack developers who want to understand how large-scale systems really work; and engineers moving into tech-lead or architecture roles.

FORMAT
PDF (A4), 418 pages, English, clickable table of contents and PDF bookmarks. 1st Edition, 2026. Published by thenexbooks.

This book is independent and is not affiliated with or endorsed by any company whose products or interview processes are mentioned. Product names are trademarks of their respective owners. Crowdline and all examples are fictional.

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