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System design learning hub

28 in-depth guides for every system design interview question that matters. Each guide covers architecture decisions, back-of-envelope numbers, failure narration, and follow-up questions — not just theory.

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Start here — process & framework
PROCESS
System Design Interview Framework
Step-by-step: clarify → estimate → design → deep dive → failures. With time allocation for each phase.
 PROCESS
Back-of-Envelope Estimation
Key numbers to memorize. QPS, storage, bandwidth formulas. Worked Twitter and URL shortener examples.
Top interview questions — design challenges
DESIGN
Design Twitter / Social Feed
Fan-out on write vs read, 23K RPS, cache stampede prevention, feed ranking at scale.
 DESIGN
Design WhatsApp / Chat System
WebSocket management at 50M concurrent, ACK chains, Cassandra for messages, Redis presence.
 DESIGN
Design YouTube / Video Streaming
Upload pipeline, DASH adaptive bitrate, CDN segment caching, eventually consistent view counter.
 DESIGN
Design a URL Shortener
Base62 encoding, cache-aside, 301 vs 302, async analytics pipeline with Kafka.
 DESIGN
Design a Rate Limiter
Token bucket vs sliding window, Redis INCR atomicity, Lua scripts, fail-open vs fail-closed.
 DESIGN
Design a Payment System
Idempotency keys, write-first design, ACID PostgreSQL, two-phase payment flow, reconciliation.
 DESIGN
Design a Notification System
Multi-channel fan-out, APNs/FCM, dual priority queues, device token registry, delivery receipts.
 DESIGN
Design Typeahead Search
295K RPS, Redis prefix cache, Elasticsearch edge n-grams, frequency aggregation, 150ms debounce.
 DESIGN
Design Uber / Ride-Sharing
Redis GEORADIUS, 250K location writes/sec, two-pass matching, surge pricing, trip state machine.
 DESIGN
Design Instagram
Direct-to-CDN upload, ML-ranked feed, Explore ANN search (Faiss), social graph in Redis.
 DESIGN
Design Google Drive / File Storage
4MB chunks, SHA-256 content addressing, check-before-upload, MVCC conflict detection.
 DESIGN
Design a Web Crawler
URL frontier, Bloom filter dedup, SimHash near-duplicate detection, politeness scheduling.
 DESIGN
Design Kafka / Message Queue
Log-based storage, partition/consumer group mechanics, ISR replication, exactly-once semantics.
 DESIGN
Design a Proximity Service
Geohashing, Redis GEORADIUS, expanding ring search, static vs moving object architectures.
Core distributed systems concepts
CONCEPT
CAP Theorem Explained
Partition tolerance is mandatory. CP vs AP systems. PACELC extension. Mapping to product semantics.
 CONCEPT
Consistent Hashing Explained
Hash ring mechanics, virtual nodes (100–200 per physical), 1/N remapping guarantee.
 CONCEPT
Distributed Caching Patterns
Cache-aside, write-through, write-behind, LRU vs LFU, cache stampede prevention, hot keys.
 CONCEPT
Chaos Engineering 101
Steady state hypothesis, blast radius, 4 principles, experiment checklist, SysSimulator chaos panel.
 CONCEPT
SQL vs NoSQL: How to Choose
4 NoSQL categories, decision rules, when to default to PostgreSQL, polyglot persistence patterns.
 CONCEPT
Database Indexing Explained
B-tree mechanics, composite index column order, covering indexes, when indexes hurt writes.
 CONCEPT
Database Sharding Strategies
Hash vs range sharding, shard key selection, hotspots, resharding with consistent hashing.
 CONCEPT
Load Balancing Algorithms
Round robin, least connections, consistent hashing, L4 vs L7, health checks, sticky sessions.
 CONCEPT
API Design: REST vs GraphQL vs gRPC
When to use each, N+1 problem, versioning strategies, cursor vs offset pagination.
 CONCEPT
Microservices vs Monolith
Real costs of distributed systems, modular monolith, service boundary design, Conway's Law.
 CONCEPT
Saga Pattern: Distributed Transactions
Choreography vs orchestration, compensating transactions, outbox pattern, idempotency.
PRACTICE

Reading isn't enough — you need to practice under interview conditions

SysSimulator lets you draw, simulate, and stress-test these architectures interactively. Load a blueprint, inject failures, and see how the numbers from these guides play out in practice. Every design article on this page has a corresponding blueprint.

Open SysSimulator → Browse blueprints