Backend System Design

Backend System Design

Study map: interview framework → core concepts → full design questions.

Start here

• Overview

  Interview structure and 45–60 minute framework
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• HLD Quick Notes

  Short revision notes for common architecture building blocks
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• Concept Questions

  Short verbal drills on CAP, cache, queues, consistency
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Core concepts

Scaling foundations

• Scaling Fundamentals

  Single server to millions of users
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• Estimation

  Back-of-envelope RPS, storage, bandwidth
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• Consistent Hashing

  Hash ring, virtual nodes, rebalance
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Building blocks

• Load Balancing

  L4/L7, algorithms, health checks, stickiness
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• Caching

  Cache-aside, write paths, eviction, stampede
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• Database Scaling

  Vertical/horizontal, replicas, sharding
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• Storage Engines

  B-tree vs LSM, WAL, compaction
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• Transactions

  ACID, isolation, distributed TX and sagas
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• Saga Pattern (HLD)

  Compensation, outbox, cross-service workflows
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• CAP & Consistency (HLD)

  CP vs AP, quorums, consistency models
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• Replication

  Leader/follower, lag, failover
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• CDN

  Edge caching, headers, invalidation
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• Availability Patterns

  Failover, circuit breaker, degradation
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• Communication Protocols

  HTTP, gRPC, WebSocket, sync vs async
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• Microservices

  Boundaries, sync/async, circuit breaker
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• Message Queues

  Producers, consumers, ACKs, Kafka vs SQS
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Design questions

Popular picks

• URL Shortener
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• Chat System
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• News Feed
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• Rate Limiter
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• Payment System
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• Notifications
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All design questions

• Key-Value Store
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• Unique ID
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• Autocomplete
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• Web Crawler
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• YouTube
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• Google Drive
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• Twitter Search
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• Distributed Cache
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• Search Engine
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• Task Scheduler
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• Metrics System
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• Booking System
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