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Big Picture: The Journey of One Request

How a large-scale website is built: all the important System Design topics (Amazon / Flipkart / Netflix scale). This guide has 64 topics, 9 parts and 390 tools explained. Every topic covers: why it is used, how it works, which tools, the difference between tools, and a real-world example. At the end there is a quick revision cheat-sheet.

The journey of one request: the whole picture first

When you press 'Buy Now' on Amazon, the request takes this path. Every box is a topic explained in detail in this guide.

The journey of one request
  1. 1.User (Browser / App)
  2. 2.DNS
  3. 3.CDN
  4. 4.WAF / DDoS
  5. 5.Load Balancer
  6. 6.API Gateway (Auth + Rate Limit)
  7. 7.Microservices
  8. 8.Cache (Redis)
  9. 9.Database (SQL / NoSQL)
  10. 10.Message Queue / Kafka
  11. 11.Workers (email, search index, analytics)

The request starts at the user and goes through DNS, CDN, WAF, LB, gateway, services, cache, DB, queue and workers

What always runs alongside

  • Logging
  • Monitoring & Alerting
  • Tracing
  • Security (TLS, secrets)
  • CI/CD
  • Kubernetes
  • Auto-scaling
  • Backups & Disaster Recovery

How to read this guide

  1. Start with Part 1: how traffic comes in.
  2. Then Caching & Database.
  3. Then Async (Queue/Kafka/Pub-Sub).
  4. Then Reliability, Security, DevOps.
  5. Last come Advanced topics (Networking, Performance, Data) and Business (Fraud, Compliance, Cost).
  6. For seeing each design end-to-end there are separate Case Studies.
  7. Every topic has a comparison table that shows the difference between tools at a glance, and a step-by-step real-world example.

Contents

PartTopics
Part 1: The Entry Gate for Traffic1 DNS & GeoDNS; 2 CDN; 3 Load Balancer (L4 vs L7, algorithms); 4 Reverse Proxy & API Gateway; 5 Rate Limiting & Throttling; 6 Scaling (Vertical vs Horizontal, Auto-scaling); 7 Stateless Servers & Session Management; 8 DDoS Protection, WAF & Bot Protection
Part 2: Caching & Database9 Caching (Redis vs Memcached vs Local Cache; Cache-aside, Write-through, Write-back, Read-through); 10 Cache Eviction, Invalidation, TTL & Cache Stampede; 11 SQL vs NoSQL; 12 Database Replication & Read Replicas; 13 Sharding / Partitioning; 14 Consistent Hashing; 15 Database Indexing & Query Optimization; 16 CAP Theorem, PACELC & Consistency Models; 17 Transactions (ACID & Distributed Transactions: 2PC, Saga, Outbox)
Part 3: Storage, Search & Data18 Object / Blob Storage vs Block vs File Storage; 19 Image & Video Processing / Streaming; 20 Search Engine (Full-Text Search); 21 Autocomplete / Typeahead; 22 Data Warehouse, ETL & Big Data Analytics; 23 Recommendation System & A/B Testing
Part 4: Async Communication & Services24 Message Queue; 25 Pub/Sub vs Message Queue vs Event Streaming; 26 Event Streaming with Kafka; 27 Background Jobs & Task Scheduling; 28 Real-time Communication (WebSocket vs SSE vs Long Polling); 29 Notification System; 30 Monolith vs Microservices; 31 API Design & Service Communication (REST vs gRPC vs GraphQL); 32 Service Discovery & Configuration Management
Part 5: Reliability & Correctness33 Timeouts, Retries, Exponential Backoff & Circuit Breaker; 34 Idempotency & Exactly-once processing; 35 High Availability, Failover, Multi-Region & Disaster Recovery; 36 Distributed Locking & Leader Election; 37 Unique ID Generation; 38 Concurrency Control (Inventory, Flash Sale & Overselling); 39 Backpressure, Load Shedding & Graceful Degradation; 40 Payment System Design
Part 6: Security & Observability41 Authentication & Authorization; 42 Encryption, HTTPS/TLS & Secrets Management; 43 Centralized Logging; 44 Monitoring, Metrics & Alerting; 45 Distributed Tracing
Part 7: Deployment, DevOps & Planning46 Containers & Orchestration; 47 CI/CD & Deployment Strategies; 48 Infrastructure as Code (IaC); 49 Load Testing, Performance Testing & Chaos Engineering; 50 Capacity Planning & Back-of-the-envelope Estimation
Part 8: Networking, Performance & Advanced Data51 TCP vs UDP, HTTP/1.1 vs HTTP/2 vs HTTP/3 (QUIC), Keep-Alive & Connection Reuse; 52 Web Performance (Compression, Browser Caching Headers, Lazy Loading, SSR vs CSR vs SSG); 53 CQRS & Event Sourcing; 54 Consensus & Cluster Coordination (Raft, Paxos, Quorum N/R/W, Gossip Protocol); 55 Probabilistic Data Structures (Bloom Filter, HyperLogLog, Count-Min Sketch); 56 Geo-spatial & Location Services (Geohash, Quadtree, S2/H3); 57 Specialised Databases (Time-series, Graph, NewSQL, Wide-column, Polyglot Persistence); 58 Zero-downtime Database Migration & Schema Changes; 59 BFF (Backend for Frontend) & Mobile Backend; 60 Large File Upload & Download
Part 9: Business, Compliance & Cost61 Fraud Detection & Risk Engine; 62 Compliance & Data Privacy (DPDP, GDPR, PCI-DSS, Data Localisation); 63 Multi-tenancy & Data Isolation; 64 Cloud Cost Optimization / FinOps