System-design workbook: foundations, building blocks, real-world systems, and postmortems.http://localhost:4321/http://localhost:4321/system-design/ai-code-assistant/http://localhost:4321/system-design/ai-code-assistant/Latency-sensitive completion, repo-aware context, indexing strategies, evaluation harness.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsllmcodeideretrievalhttp://localhost:4321/system-design/abstractions-in-distributed-systems/http://localhost:4321/system-design/abstractions-in-distributed-systems/What an interviewer means when they say 'service', 'node', 'cluster' — the unit boundaries that shape every design.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationsdistributed-systemsvocabularyfundamentalshttp://localhost:4321/system-design/availability/http://localhost:4321/system-design/availability/Nines as a budget, redundancy strategies, failover modes, and the cost of each 9.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptNon-Functional Requirementsavailabilitynfrslahttp://localhost:4321/system-design/aws-kinesis-2020/http://localhost:4321/system-design/aws-kinesis-2020/Thread-limit exhaustion cascaded across services that depended on Kinesis for control-plane operations.Sat, 16 May 2026 00:00:00 GMTIntermediatepostmortemPostmortemsawscascading-failurecontrol-planethread-poolhttp://localhost:4321/system-design/aws-us-east-1-2023/http://localhost:4321/system-design/aws-us-east-1-2023/Why one region keeps taking down half the internet, and what 'control plane in one region' really costs.Sat, 16 May 2026 00:00:00 GMTIntermediatepostmortemPostmortemsawsregioncontrol-planeblast-radiushttp://localhost:4321/system-design/blob-store/http://localhost:4321/system-design/blob-store/Object storage with metadata indexing: chunking, replication, lifecycle, multipart uploads.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksstorageobject-storagedurabilityhttp://localhost:4321/system-design/chatgpt-system/http://localhost:4321/system-design/chatgpt-system/Streaming inference, KV-cache reuse, request routing, safety filters, multi-tenant GPU scheduling.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsllminferencegpustreaminghttp://localhost:4321/system-design/client-side-error-monitoring/http://localhost:4321/system-design/client-side-error-monitoring/Browser and mobile error capture, sampling, PII scrubbing, beacon transport.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksobservabilityerrorsfrontendhttp://localhost:4321/system-design/capacity-estimation-cheatsheet/http://localhost:4321/system-design/capacity-estimation-cheatsheet/Latencies, throughputs, sizes, and conversion shortcuts to keep in your head for back-of-envelope math.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationscapacity-planningestimationinterview-prephttp://localhost:4321/system-design/cloudflare-2019-regex/http://localhost:4321/system-design/cloudflare-2019-regex/A single WAF rule with exponential regex backtracking burned 100% CPU across every edge node simultaneously.Sat, 16 May 2026 00:00:00 GMTFoundationalpostmortemPostmortemsregexcpuwafglobal-deployhttp://localhost:4321/system-design/consistency-models/http://localhost:4321/system-design/consistency-models/From strong to eventual: linearizability, sequential, causal, monotonic, eventual — what each costs and what each buys.Sat, 16 May 2026 00:00:00 GMTIntermediateconceptFoundationsconsistencydistributed-systemscaphttp://localhost:4321/system-design/content-delivery-network/http://localhost:4321/system-design/content-delivery-network/Edge caching, origin shielding, push vs pull, cache invalidation, signed URLs.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blockscdnedgecachinghttp://localhost:4321/system-design/code-deployment-system/http://localhost:4321/system-design/code-deployment-system/Pipelines, artifact stores, environment promotion, canary / blue-green / rolling, rollback.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designscicddeploymentcanaryrollbackhttp://localhost:4321/system-design/distributed-logging/http://localhost:4321/system-design/distributed-logging/Log shipping, structured fields, aggregation, retention tiers, search-on-logs vs metrics.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksloggingobservabilitylog-aggregationhttp://localhost:4321/system-design/databases/http://localhost:4321/system-design/databases/Relational vs document vs wide-column vs graph: when each shape fits, and the trade-off triangle.Sat, 16 May 2026 00:00:00 GMTFoundationalbuilding-blockBuilding Blocksdatabasesstoragedata-modelinghttp://localhost:4321/system-design/distributed-cache/http://localhost:4321/system-design/distributed-cache/Memcached vs Redis, sharding, eviction policies, replication, stampede protection.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blockscachingdistributed-systemsperformancehttp://localhost:4321/system-design/distributed-messaging-queue/http://localhost:4321/system-design/distributed-messaging-queue/FIFO vs at-least-once vs exactly-once, partitions, consumer groups, dead-letter queues.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksmessagingasyncqueueshttp://localhost:4321/system-design/distributed-monitoring/http://localhost:4321/system-design/distributed-monitoring/Metrics, logs, traces — the three pillars and the data structures that scale each.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksobservabilitymetricstracinghttp://localhost:4321/system-design/distributed-search/http://localhost:4321/system-design/distributed-search/Inverted indexes, sharded indexing, replication, query fan-out, ranking pipelines.Sat, 16 May 2026 00:00:00 GMTAdvancedbuilding-blockBuilding Blockssearchinverted-indexrankinghttp://localhost:4321/system-design/distributed-task-scheduler/http://localhost:4321/system-design/distributed-task-scheduler/Priority, idempotency, deduplication, retry policies, resource capacity allocation.Sat, 16 May 2026 00:00:00 GMTAdvancedbuilding-blockBuilding Blocksschedulerjobsworkflowhttp://localhost:4321/system-design/dns/http://localhost:4321/system-design/dns/Hierarchical name resolution, caching, TTL trade-offs, and DNS as a load-balancing primitive.Sat, 16 May 2026 00:00:00 GMTFoundationalbuilding-blockBuilding Blocksdnsnetworkingcachinghttp://localhost:4321/system-design/dropbox/http://localhost:4321/system-design/dropbox/Client-side chunked replication, conflict resolution across devices, delta sync, and the LAN sync trick. Canonical 'consumer cloud storage' design.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsstoragesyncchunkingconflict-resolutionhttp://localhost:4321/system-design/facebook-messenger/http://localhost:4321/system-design/facebook-messenger/Real-time messaging with rich threads, reactions, typing indicators, and read receipts. WhatsApp's cousin with web-first reach and a different presence model.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsmessagingwebsocketspresencefan-outhttp://localhost:4321/system-design/failure-models/http://localhost:4321/system-design/failure-models/Crash-stop, crash-recovery, omission, Byzantine — the assumption stack under every fault-tolerance claim.Sat, 16 May 2026 00:00:00 GMTIntermediateconceptFoundationsfailure-modesdistributed-systemsfault-tolerancehttp://localhost:4321/system-design/facebook-2021-bgp-outage/http://localhost:4321/system-design/facebook-2021-bgp-outage/A routine BGP maintenance command withdrew Facebook from the internet. Six hours of global blackout; internal tools and badge readers locked out of the buildings that hosted the fix.Sat, 16 May 2026 00:00:00 GMTFoundationalpostmortemPostmortemsbgpdnsblast-radiuscontrol-planehttp://localhost:4321/system-design/fault-tolerance/http://localhost:4321/system-design/fault-tolerance/Designing for the worst expected failure and degrading gracefully past it.Sat, 16 May 2026 00:00:00 GMTIntermediateconceptNon-Functional Requirementsfault-tolerancenfrresiliencehttp://localhost:4321/system-design/google-maps/http://localhost:4321/system-design/google-maps/Map tiles, routing on a road graph, ETA prediction, real-time traffic ingestion.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsgeoroutingtilesgraphhttp://localhost:4321/system-design/instagram/http://localhost:4321/system-design/instagram/Photo upload, feed generation, story expiration, following graph.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsfeedmediafan-outsocial-graphhttp://localhost:4321/system-design/google-docs/http://localhost:4321/system-design/google-docs/Operational transforms vs CRDTs, presence, conflict resolution, offline edits.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designscollaborationotcrdtwebsocketshttp://localhost:4321/system-design/interview-frameworks-compared/http://localhost:4321/system-design/interview-frameworks-compared/8-step, 4-step, SNAKE, PACELC-flavored — what each emphasizes and which to anchor on under pressure.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationsframeworkinterview-prepcomparisonhttp://localhost:4321/system-design/key-value-store/http://localhost:4321/system-design/key-value-store/Consistent-hash ring, replication factor, versioning (vector clocks), failure detection. Dynamo-style design.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blockskey-valuedistributed-storageconsistent-hashinghttp://localhost:4321/system-design/maintainability/http://localhost:4321/system-design/maintainability/The operational burden of every architectural decision: observability, deployability, on-call load.Sat, 16 May 2026 00:00:00 GMTIntermediateconceptNon-Functional Requirementsmaintainabilitynfroperationshttp://localhost:4321/system-design/llm-customer-support-bot/http://localhost:4321/system-design/llm-customer-support-bot/RAG over knowledge bases, conversation memory, escalation handoff, guardrails.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsllmragsupportescalationhttp://localhost:4321/system-design/load-balancers/http://localhost:4321/system-design/load-balancers/L4 vs L7, global vs local, algorithms (round-robin, least-connections, consistent-hash), placement tiers.Sat, 16 May 2026 00:00:00 GMTFoundationalbuilding-blockBuilding Blocksload-balancingnetworkingtraffic-routinghttp://localhost:4321/system-design/ml-data-infrastructure/http://localhost:4321/system-design/ml-data-infrastructure/Feature stores, training data pipelines, online vs batch features, lineage, vector storage.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsmlfeature-storetrainingvector-dbhttp://localhost:4321/system-design/newsfeed-system/http://localhost:4321/system-design/newsfeed-system/Pluggable feed engine: ranking, freshness, deduplication, infinite scroll, caching strategy.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsfeedrankingfan-outcachinghttp://localhost:4321/system-design/nfrs-in-interviews/http://localhost:4321/system-design/nfrs-in-interviews/Which non-functional requirements to surface, in what order, and how to convert vague asks into numbers.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptNon-Functional Requirementsnfrinterview-preprequirementshttp://localhost:4321/system-design/pub-sub/http://localhost:4321/system-design/pub-sub/Topic-based fan-out, ordering guarantees, filtering, retention, and the gap between pub-sub and queues.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksmessagingpub-subevent-drivenhttp://localhost:4321/system-design/payment-system/http://localhost:4321/system-design/payment-system/Idempotency, double-entry ledgers, reconciliation, gateway integration, fraud signals.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designspaymentsledgeridempotencyreconciliationhttp://localhost:4321/system-design/proximity-service-yelp/http://localhost:4321/system-design/proximity-service-yelp/Geo-indexing, dynamic segments, search-within-radius queries at city scale.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsgeosearchindexingrankinghttp://localhost:4321/system-design/quora/http://localhost:4321/system-design/quora/Q&A platform: ranking answers, follow graph, notification fan-out, search.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsqarankingfeedsearchhttp://localhost:4321/system-design/reliability/http://localhost:4321/system-design/reliability/Probability of working under expected conditions; how it differs from availability and where the trade-offs live.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptNon-Functional Requirementsreliabilitynfrcorrectnesshttp://localhost:4321/system-design/rate-limiter/http://localhost:4321/system-design/rate-limiter/Cap request rates per client to protect downstream services. Token bucket vs leaky bucket vs sliding window, with the gotchas of distributed coordination.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksrate-limitingdistributed-systemsapi-gatewayhttp://localhost:4321/system-design/remote-procedure-calls/http://localhost:4321/system-design/remote-procedure-calls/Network abstractions over function-call semantics: gRPC, Thrift, REST-as-RPC, the leaks they hide and don't.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationsrpcnetworkingapi-designhttp://localhost:4321/system-design/ride-hailing-eats/http://localhost:4321/system-design/ride-hailing-eats/Three-sided marketplace: restaurants, couriers, customers. Order routing, ETA, courier dispatch.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsmarketplacedispatchgeoreal-timehttp://localhost:4321/system-design/scalability/http://localhost:4321/system-design/scalability/Vertical, horizontal, and elasticity. Why naive scaling stalls and which axis to pick first.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptNon-Functional Requirementsscalabilitynfrcapacity-planninghttp://localhost:4321/system-design/resource-estimation-examples/http://localhost:4321/system-design/resource-estimation-examples/Four end-to-end estimation walk-throughs (Twitter, YouTube, WhatsApp, a search index) — the math anchored to the Foundations cheatsheet.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationsestimationcapacity-planninginterview-prephttp://localhost:4321/system-design/sequencer/http://localhost:4321/system-design/sequencer/Globally-ordered unique IDs with causality. Snowflake, TrueTime, hybrid logical clocks.Sat, 16 May 2026 00:00:00 GMTAdvancedbuilding-blockBuilding Blocksdistributed-systemsidsorderinghttp://localhost:4321/system-design/server-side-error-monitoring/http://localhost:4321/system-design/server-side-error-monitoring/Real-time error capture, deduplication, alerting, blast-radius scoping.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blocksobservabilityerrorsalertinghttp://localhost:4321/system-design/sharded-counters/http://localhost:4321/system-design/sharded-counters/Decompose a hot counter into N shards and aggregate on read — the canonical fix for write hotspots.Sat, 16 May 2026 00:00:00 GMTIntermediatebuilding-blockBuilding Blockscounterswrite-hotspotshardinghttp://localhost:4321/system-design/spotify-wrapped/http://localhost:4321/system-design/spotify-wrapped/Annual per-user retrospective from a year of plays. Massively-parallel batch pipeline, per-user partitioning, and the once-a-year cost shape.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsbatchanalyticsmapreducepartitioninghttp://localhost:4321/system-design/the-system-design-walkthrough/http://localhost:4321/system-design/the-system-design-walkthrough/A repeatable interview framework — clarify, estimate, contract, high-level, data, detail, evaluate. Read this first; every system writeup on this site follows it.Sat, 16 May 2026 00:00:00 GMTFoundationalconceptFoundationsframeworkinterview-prephttp://localhost:4321/system-design/tiktok/http://localhost:4321/system-design/tiktok/Short-form video at hyperscale. The for-you ranking pipeline is the design — recommendation, signal collection, and freshness vs personalization trade-offs.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsrecommendationvideorankingml-servinghttp://localhost:4321/system-design/twitter-newsfeed/http://localhost:4321/system-design/twitter-newsfeed/Generate a personalized timeline at read time, write time, or both. The pull / push / hybrid trade-off and the celebrity-fanout problem.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsnewsfeedfan-outsocial-graphcachinghttp://localhost:4321/system-design/typeahead-suggestion/http://localhost:4321/system-design/typeahead-suggestion/Real-time prefix matching: trie indexes, ranking, server-side throttling, personalization.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designstrieautocompletesearchrankinghttp://localhost:4321/system-design/uber/http://localhost:4321/system-design/uber/Driver / rider matching, real-time location, surge pricing, payments, fraud detection.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsgeomatchingreal-timemarketplacehttp://localhost:4321/system-design/url-shortener/http://localhost:4321/system-design/url-shortener/Map long URLs to short ones, redirect in O(1), survive billions of clicks. The canonical first system to whiteboard — sharp scope, real scale, every primitive in play.Sat, 16 May 2026 00:00:00 GMTFoundationalsystemSystem Designshash-mapkv-storeredirectanalyticshttp://localhost:4321/system-design/ticketmaster/http://localhost:4321/system-design/ticketmaster/Inventory reservation under coordinated burst load: waiting rooms, holds, atomic seat allocation, and the bot-vs-fan arms race.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsinventoryflash-salequeueinganti-abusehttp://localhost:4321/system-design/web-crawler/http://localhost:4321/system-design/web-crawler/URL frontier, politeness, deduplication, content extraction, crawl traps, index updates.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designscrawlingfrontierdeduppolitenesshttp://localhost:4321/system-design/whatsapp/http://localhost:4321/system-design/whatsapp/End-to-end-encrypted messaging at scale: presence, delivery receipts, group chats, media.Sat, 16 May 2026 00:00:00 GMTIntermediatesystemSystem Designsmessaginge2eewebsocketspresencehttp://localhost:4321/system-design/youtube/http://localhost:4321/system-design/youtube/Video upload, encoding pipeline, CDN-backed delivery, watch-history, recommendations.Sat, 16 May 2026 00:00:00 GMTAdvancedsystemSystem Designsvideocdntranscodingstorage