System Design
System Design Guides
37From scaling fundamentals to full interview designs like YouTube and Uber: architectures, trade-offs, capacity math, and the questions interviewers actually probe on.
Fundamentals11 articles
Fundamentals
Scaling: Vertical vs Horizontal, and the Path to a Million Users
How vertical and horizontal scaling actually work, when to reach for each, and the real numbers behind replicas, sharding, and back-pressure at scale.
9 min read
Fundamentals
SQL vs NoSQL: How to Actually Choose a Database
A practical SQL vs NoSQL guide — ACID, schemas, sharding, query-first modeling, and the interview trade-offs that decide which database fits your workload.
9 min read
Fundamentals
CAP Theorem: What You Actually Give Up During a Partition
A precise guide to the CAP theorem — what consistency, availability, and partition tolerance mean, why you only ever choose C or A, and how CP and AP systems behave.
10 min read
Fundamentals
Caching: Strategies, Eviction, and the Failure Modes That Bite
How caching actually works in a real system — cache-aside vs write-through, LRU vs LFU eviction, thundering herd, and the stale-data bugs that bite in production.
11 min read
Fundamentals
Load Balancing: How One Address Fans Out to a Hundred Servers
How load balancers spread traffic across servers — L4 vs L7, round-robin vs power-of-two-choices, health checks, sticky sessions, and global routing.
10 min read
Fundamentals
CDN: How Content Delivery Networks Actually Work
How a CDN cuts latency and origin load — edge caching, pull vs push, anycast routing, cache headers, invalidation, and the trade-offs interviewers probe.
10 min read
Fundamentals
Message Queues: Kafka, RabbitMQ, and the Guarantees That Matter
How message queues decouple services — Kafka vs RabbitMQ, at-least-once vs exactly-once delivery, ordering by partition key, and dead-letter recovery.
9 min read
Fundamentals
Consistent Hashing: Add and Remove Nodes Without Reshuffling Everything
How consistent hashing maps keys and nodes onto a ring so adding a server moves only ~1/N of keys — plus virtual nodes, replication, and interview trade-offs.
9 min read
Fundamentals
API Gateway: The Single Front Door for Microservices
How an API gateway handles routing, authentication, rate limiting, and aggregation for microservices — the trade-offs and interview decisions that matter.
9 min read
Fundamentals
Database Indexing: How the Right Index Turns a Table Scan into a Log-N Lookup
How database indexes work, why B+trees dominate, and how to choose composite, covering, partial, and LSM indexes without wrecking write throughput.
10 min read
Fundamentals
Networking Essentials
Networking Essentials: an engineer-focused guide to the requirements, trade-offs, architecture, and interview decisions that matter.
3 min read
Core Designs11 articles
Core Designs
Design a URL Shortener: The System Design Interview Classic
Design a URL shortener like Bitly — capacity math, base62 vs hashing for short codes, the read path, caching, and how to survive a viral link.
9 min read
Core Designs
Design a Rate Limiter: Token Bucket, Redis, and Real Trade-offs
How to design a distributed API rate limiter — token bucket vs sliding window, an atomic Redis implementation, capacity numbers, and fail-open trade-offs.
11 min read
Core Designs
Design a Key-Value Store: Consistent Hashing, Quorums, and Conflict Resolution
How to design a distributed key-value store like DynamoDB — consistent hashing, N/R/W quorums, vector clocks, Merkle-tree recovery, and LSM storage engines.
11 min read
Core Designs
Design a Notification System: Push, Email & SMS at Scale
How to design a multi-channel notification system for push, email, and SMS — the queue, dispatcher, dedup, retries, and a 50M-user fan-out walkthrough.
11 min read
Core Designs
Design a Chat System: Real-Time Messaging at WhatsApp Scale
A concrete walkthrough of designing a real-time chat system like WhatsApp — WebSockets, session routing, message storage, ordering, presence, and capacity math.
10 min read
Core Designs
Design a News Feed: Fanout, Ranking, and the Celebrity Problem
How to design a scalable news feed — fanout-on-write vs fanout-on-read, the hybrid model, feed caching, ranking, and the capacity math interviewers ask for.
10 min read
Core Designs
Design a Web Crawler: Frontier, Politeness, and Dedup at Scale
How to design a distributed web crawler — the URL frontier, per-host politeness, Bloom-filter dedup, freshness recrawls, and capacity math for 1B pages a day.
9 min read
Core Designs
Design an Autocomplete System
How to design an autocomplete / typeahead system — the prefix trie, top-K caching, ranking signals, sharding, fuzzy match, and the numbers interviewers probe.
9 min read
Core Designs
Design a Unique ID Generator: Snowflake, UUIDs, and Distributed Clocks
How to design a distributed unique ID generator — Snowflake's 64-bit layout, UUID vs sequence trade-offs, worker-ID leasing, and clock-skew handling.
8 min read
Core Designs
Design a Distributed Task Scheduler
How to design a distributed task scheduler: cron storage, leader election, timing wheels, misfire recovery, and at-least-once delivery with idempotency.
11 min read
Core Designs
Design a Leaderboard: Real-Time Ranking at Scale
How to design a real-time leaderboard with Redis sorted sets — score updates, top-K, rank queries, tie-breaking, sharding, and durability, with concrete numbers.
11 min read
Advanced Designs15 articles
Advanced Designs
Design YouTube: Upload Pipeline, CDN, and Video at Planet Scale
How to design YouTube in a system design interview — the transcoding DAG, ABR streaming, multi-tier CDN, storage tiering, view counting, and capacity math.
8 min read
Advanced Designs
Design Instagram: Feed Fanout, Stories, and Ranking at Scale
Design Instagram end to end — capacity math for 500M DAU, hybrid feed fanout, Stories with 24h TTL, sharding, and ML ranking within a 200ms budget.
10 min read
Advanced Designs
Design Twitter: Fanout, Timelines, and the Celebrity Problem
How to design Twitter in a system design interview — fanout-on-write vs read, the celebrity problem, capacity math, timeline caching, search, and trending topics.
9 min read
Advanced Designs
Design Uber: Dispatch, Spatial Indexing, and Real-Time Location
How to design Uber in a system design interview — H3 spatial indexing, driver-rider dispatch without double-booking, location ingestion, surge pricing, and ETA.
8 min read
Advanced Designs
Design Google Maps: Tiles, Routing, and Real-Time Traffic
How to design Google Maps in a system design interview — the tile pyramid, Contraction Hierarchies routing, real-time traffic ingestion, and capacity math.
9 min read
Advanced Designs
Design Netflix: Streaming, OpenConnect, and Recommendations at Scale
How to design Netflix in a system design interview — ABR streaming, OpenConnect CDN, DRM, capacity math for 250M users, and the recommendations serving path.
11 min read
Advanced Designs
Design Spotify: Streaming, Playlists, and Discover Weekly at Scale
A system design walkthrough for Spotify — audio delivery, capacity math for 100M DAU, collaborative playlists, Discover Weekly, and Spotify Connect.
9 min read
Advanced Designs
Design Discord: Real-Time Chat, Voice, and Presence at Scale
How to design Discord in a system design interview — the WebSocket gateway, Cassandra message store, WebRTC SFU voice, and presence fan-out at scale.
11 min read
Advanced Designs
Design Slack: Channels, Threads, and Search That Stays Fast
How to design Slack in a system design interview — the WebSocket gateway, thread data model, permission-aware search, boot payload, and notification fan-out.
11 min read
Advanced Designs
Design Google Drive: Chunking, Sync, and Real-Time Collaboration
How to design Google Drive in a system design interview — content-addressed chunking, block-level sync, ACLs, and real-time collaboration with real capacity numbers.
10 min read
Advanced Designs
Design Ticketmaster: Selling 100k Seats Without Overselling One
How to design Ticketmaster for a Taylor Swift on-sale — seat holds, virtual waiting rooms, capacity math, and the two-phase lock that prevents overselling.
8 min read
Advanced Designs
Design a Payment System: Ledgers, Idempotency, and Sagas
Design a payment system like Stripe — idempotency keys, a double-entry ledger, PCI scope, saga orchestration, webhook handling, and real capacity math.
10 min read
Advanced Designs
Design a Search Engine: Inverted Indexes, BM25, and Web-Scale Retrieval
How to design a web search engine — inverted indexes, BM25 ranking, crawler-to-indexer pipeline, document sharding, and capacity math for 50B documents.
10 min read
Advanced Designs
Design a Top-K Service: Trending Items at a Million Events a Second
Design a top-K trending service — count-min sketch plus a min-heap, sliding windows, sharded merges, and the capacity math for 1M events/sec over 500M items.
8 min read
Advanced Designs
Design a Proximity Service: Geohash, Quadtree & S2 at Scale
How to design a proximity service like Yelp — spatial indexing with geohash, quadtree, and S2, capacity math, radius search, and the live-location pipeline.
10 min read
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