Case Studies
56 end-to-end system designs.
- Systems
- 56
- Hours
- 29
- 8.0
URL Shortener (TinyURL / bit.ly)
An interview-grade walkthrough for a URL shortener: capacity estimation, short-code generation, hot-key caching, and an analytics pipeline that never blocks the redirect.
DynamoDBRedisCloudflare+5 - 8.1
Pastebin (Paste Sharing Service)
An interview-grade walkthrough for a Pastebin-style text sharing service: object storage split, TTL-based expiration pipelines, syntax highlighting placement, and abuse prevention.
S3DynamoDBRedis+3 - 8.2
Distributed Rate Limiter
An interview-grade walkthrough for a distributed API rate limiter: algorithm choice, Redis Lua atomicity, two-tier local+global synchronization, and fail-open failure modes.
RedisEnvoyNginx+3 - 8.3
Distributed Key-Value Store (Dynamo / Cassandra / Riak)
Design a distributed KV store with consistent hashing, quorum replication, gossip membership, hinted handoff, and Merkle-tree anti-entropy repair.
CassandraScyllaDBDynamoDB - 8.4
Notification System (Push, SMS, Email at Scale)
An interview-grade walkthrough for a multi-channel notification platform: fan-out architecture, APNs/FCM integration, retry with dead-letter queues, and device-token lifecycle.
KafkaRedisCassandra+3 - 8.5
Chat System (WhatsApp / Messenger / Signal)
Staff-level design for 1:1 and small-group chat at WhatsApp scale: 500M concurrent connections, message ordering, E2E encryption, and storage model trade-offs.
ScyllaDBCassandraRedis+7 - 8.6
Social Media Feed (Twitter / Instagram / LinkedIn)
Fan-out architecture, hybrid push/pull, ML ranking pipelines, and the celebrity problem at Twitter/X scale.
RedisKafkaCassandra+4 - 8.7
Photo Sharing Service (Instagram)
Design Instagram-scale photo sharing: upload pipeline, transcoding, multi-resolution image serving, CDN with origin shielding, and news feed integration.
PostgreSQLS3CloudFront+4 - 8.8
Web Crawler (Googlebot-style)
Design a distributed web crawler with URL frontier, politeness policies, content deduplication, robots.txt compliance, and Bloom-filter-backed URL dedup at billion scale.
KafkaCassandraHBase+3 - 8.9
Search Autocomplete (Typeahead Suggestions)
Design a low-latency autocomplete system with tries, top-K precomputation, real-time trending overlays, and multi-tier caching at Google scale.
RedisElasticsearchKafka+3 - 8.10
Video Streaming Service (YouTube / Twitch / TikTok)
Design a UGC video platform from upload through adaptive bitrate streaming: transcode pipeline, HLS/DASH/CMAF packaging, CDN delivery with ISP peering, and live ingest architecture.
S3KafkaCloudFront+3 - 8.11
Netflix (End-to-End)
A whole-system walkthrough of Netflix's architecture: microservices, Open Connect CDN, per-title encoding, Cassandra + EVCache, resilience patterns, and chaos engineering.
CassandraMemcachedKafka+4 - 8.12
Ride-Hailing Service (Uber / Lyft)
An interview-grade walkthrough for Uber-scale ride-hailing: H3 geospatial indexing, real-time location ingest, batched bipartite matching, surge pricing, and trip orchestration.
KafkaFlinkCassandra+3 - 8.13
Google Maps (Routing and Tile Rendering)
Design planet-scale mapping: map tile rendering, shortest-path routing with contraction hierarchies, ETA prediction with GNNs, and offline maps.
RedisKafkaFlink+3 - 8.14
File Sync Service (Dropbox / Google Drive)
Design a Dropbox-style file sync service: block-level deduplication, delta sync, conflict resolution, versioning, and client-server reconciliation.
MySQLS3Kafka+1 - 8.15
Collaborative Editing (Google Docs / Figma / Notion)
Staff-level design for real-time collaborative editing at 100K+ concurrent editors: OT vs CRDTs, presence broadcasting, offline sync, and version history.
WebSocketsPostgreSQLRedis+1 - 8.16
Distributed Cache (Memcached / Redis Cluster)
Design a Memcached- or Redis-style distributed cache: consistent hashing, eviction, replication, client-side sharding, and hot-key mitigation.
RedisMemcachedKafka - 8.17
Recommendation System (Netflix / YouTube / TikTok)
Design a two-stage recommendation system: candidate generation, ranking, collaborative filtering, content-based features, a feature store, and cold-start handling.
KafkaFaissRedis+1 - 8.18
Ticketing System (BookMyShow / Ticketmaster)
An interview-grade walkthrough for high-concurrency ticketing: seat locking with Redis SETNX, saga-based payment, virtual waiting rooms, and anti-bot defenses at 500M tickets/year scale.
RedisPostgreSQLKafka+5 - 8.19
Payment System (Stripe / PayPal)
Design a payment system with a double-entry ledger, idempotency keys, saga-orchestrated cross-service flows, and the compliance constraints that shape every decision.
PostgreSQLRedisKafka+3 - 8.20
Stock Exchange (Matching Engine)
Design a deterministic, low-latency matching engine: FIFO order book, price-time priority, multicast market data distribution, and co-location realities.
- 8.21
Food Delivery Service (DoorDash / Swiggy)
Design a three-sided food delivery marketplace: dispatch with batching and reassignment, composite ETA prediction, and driver-merchant-customer coordination.
KafkaRedisCassandra+3 - 8.22
Metrics Pipeline (Prometheus / InfluxDB / Thanos)
Design a time-series metrics pipeline: high-cardinality ingestion, aggregation across clusters with Thanos or Cortex, alerting, and downsampling for long-term retention.
PrometheusGrafanaOpenTelemetry+3 - 8.23
Ad-Click Aggregation (Real-Time Stream Processing)
Design an ad-click aggregation system with exactly-once semantics on Kafka + Flink, real-time fraud detection, and low-latency dashboards.
KafkaFlinkRedis+6 - 8.24
Logging Platform (ELK / Loki / Splunk)
Design a logging platform: ingestion at scale, index vs. label-based storage (Elastic vs Loki), retention tiering, and full-text search with BM25.
ElasticsearchKafkaClickHouse+3 - 8.25
Proximity Service (Nearby Friends / Yelp)
Design a proximity service for 100M users with 1M concurrent location-sharing sessions: geohash/H3/S2 trade-offs, Redis geosets, bounding-box query fan-out, privacy, and hotspot handling during events.
RedisKafkaPostgreSQL - 8.26
Real-Time Leaderboard
Design a real-time leaderboard for 10M players with 100K score updates/sec, tie-breaking, time-windowed views, friend boards, and approximate rank for the tail.
RedisKafkaDynamoDB+1 - 8.27
Unique ID Generator (Snowflake, ULID, TSID, UUIDv7)
Design a distributed ID generator producing 10M 64-bit IDs/sec, monotonic-ish ordering, clock-skew resilience, and the four-way trade-off between Snowflake, ULID, TSID, and UUIDv7.
PostgreSQLMySQLZooKeeper+1 - 8.28
Hotel Reservation System (Booking.com / Airbnb)
Staff-level design for hotel reservation: search/booking split, PostgreSQL exclusion constraints for date-range double-booking prevention, Temporal saga orchestration, and CDC-backed availability indexing at 85K QPS.
PostgreSQLRedisElasticsearch+4 - 8.29
Distributed Job Scheduler (Airflow / Temporal / Distributed Cron)
Design a scheduler for 100k registered jobs and 10k executions/sec with exactly-once execution, DAGs up to 10k nodes, late/missed run policies, and graceful scheduler upgrades.
KafkaCassandraRedis+4 - 8.30
ChatGPT (Conversational AI at Scale)
Design ChatGPT for 900M weekly users: multi-tenant LLM serving, session-state architecture, streaming SSE, per-user memory, safety, and multi-region deployment.
PostgreSQLRedisCloudflare+1 - 8.31
Enterprise RAG System
Design a multi-tenant enterprise RAG platform for 1k tenants with 10M documents each at 100 QPS/tenant: ingestion, hybrid retrieval, reranking, citation, access-control-aware retrieval, freshness, and tenant isolation.
PineconeWeaviateKafka+4 - 8.32
Coding Agent (Claude Code / GitHub Copilot / Cursor)
Design a coding agent serving 1M concurrent sessions across autocomplete, chat, and autonomous loop modes with repo indexing, sandboxed tool use, and streaming diff application.
RedisPostgreSQLgRPC+1 - 8.33
Perplexity (AI Search with Citations)
Design an AI search engine for 50M MAU, 5k QPS peak, <2 s answer latency with inline citations: query rewriting, source retrieval, citation-grounding, streaming output, freshness, and fact-check post-processing.
RedisCloudflare - 8.34
Voice Agent (Alexa / Siri-Class Realtime)
Design a realtime voice agent for 100M devices with 50k concurrent conversations and sub-700 ms turn latency: streaming ASR, LLM turn-taking, streaming TTS, WebRTC transport, and barge-in.
RedisWebSockets - 8.35
Content Moderation System at Scale
Design moderation for 500M posts/day with <200 ms pre-publish latency, human-in-loop for 0.5% of traffic, multi-modal (text+image+video): classifier cascade, reviewer workflow, appeals, adversarial robustness.
RedisKafkaClickHouse - 8.36
Semantic Cache for LLM Applications
Design an embedding-similarity cache for LLM prompts at 10k QPS, 70%+ hit rate, <10 ms lookup: similarity threshold calibration, invalidation on source change, per-tenant isolation, false-positive cost accounting.
RedisMilvusKafka+2 - 8.37
Model Router and Gateway (OpenRouter / LiteLLM)
Design a gateway routing 20k QPS across 50+ models and 10 providers with <30 ms routing overhead: cost/latency/quality routing strategies, provider failover, streaming pass-through, per-tenant quotas, cost attribution.
RedisKafkaClickHouse+1 - 8.38
Feature Flag Service (LaunchDarkly / Harness FME / Unleash)
Design a feature flag and experimentation platform for 20T evaluations/day with sub-millisecond SDK-side latency, streaming config distribution, and sub-60s kill-switch propagation.
PostgreSQLKafkaClickHouse+5 - 8.39
DNS Service (Cloudflare 1.1.1.1 / Google 8.8.8.8)
Design a public recursive DNS resolver serving trillions of queries/day globally with <20 ms p99 from 300+ anycast POPs: UDP/TCP/DoT/DoH/DoQ, DNSSEC validation, cache design, rate limiting, and DDoS survivability.
Cloudflare - 8.40
Dating App (Tinder / Hinge / Bumble)
Design a dating app for 100M MAU handling 1.5B swipes/day with <50 ms card loads: two-tower recommendations, geospatial filtering, mutual-match detection, and safety-at-scale.
RedisKafkaDynamoDB+3 - 8.41
Online Auction (eBay / Catawiki)
Design an online auction for 100M active listings and 10M concurrent bidders: Redis Lua CAS for atomic bids at 1M/sec peak, proxy bidding, sniping extensions, and WebSocket fan-out.
RedisKafkaWebSockets+2 - 8.42
Multi-Tenant SaaS Platform
Design a multi-tenant SaaS platform serving 50K tenants with per-tenant SLA tiers, metered billing, noisy-neighbor containment, and zero cross-tenant data leakage.
PostgreSQLRedisKafka+3 - 8.43
Video Conferencing System (Zoom / Google Meet)
Design a video conferencing platform for 500K simultaneous meetings and 10M concurrent participants with <150 ms audio and <500 ms video: SFU vs MCU vs P2P, simulcast and SVC, bandwidth estimation, regional media routing, and real-time recording.
RedisPostgreSQLS3+2 - 8.44
Email Service at Gmail Scale (1.8B Users, 300B Messages/Day)
Design a global email service for 1.8B users and 300B messages/day: SMTP ingress, spam pipeline cascade, per-user sharded search, RFC 5322 threading, and exabyte-scale tiered storage with content-addressed attachment dedup.
BigtableKafkaElasticsearch+3 - 8.45
Live Comments at Scale (FB Live / YouTube Live / Twitch Chat)
Design a live-comment system for 10M concurrent viewers and 100K commenters on one stream: delta-batched fan-out, pre-publish moderation, and the celebrity-stream hotspot.
RedisKafkaWebSockets - 8.46
Fraud Detection System (Stripe Radar / PayPal / Feedzai)
Design a real-time fraud detection service scoring millions of events per second under 100 ms p99 with a rules-ML cascade, online/offline feature store, graph ring detection, and analyst feedback loop.
KafkaFlinkRedis+3 - 8.47
Fitness Tracking Service (Strava / MapMyRun)
Design a fitness tracking service for 195M+ users: GPS ingestion, two-stage segment matching with H3 pre-filter and DTW, Kafka-backed leaderboards, and privacy-safe planetary heatmaps.
RedisKafkaSpark+3 - 8.48
Online Judge (LeetCode / Codeforces / HackerEarth)
Design an online judge for 1M users at 100K submissions/hour peak with <15s verdict p99: Firecracker sandboxes, priority queueing for contests, seccomp + cgroups isolation, and MOSS-style plagiarism detection.
PostgreSQLRedisRabbitMQ+1 - 8.49
Price Tracking Service (CamelCamelCamel / Honey / Keepa)
Design a price-tracking service that watches 100M product URLs with priority-driven scraping, diff-based alerting to 10M subscribers, 2-year historical retention, and polite rotation through a proxy pool that retailers actively try to block.
KafkaRedisPostgreSQL+4 - 8.50
API Gateway at Scale (Kong / AWS API Gateway / Apigee / Envoy)
Design an API gateway that handles 100K RPS per instance with <5 ms p99 overhead across 10K upstream services: routing trie, local+global rate limiting, mTLS termination, hitless config reload, and circuit breaking.
EnvoyKongNginx+5 - 8.51
CI/CD Platform (GitHub Actions / GitLab CI / CircleCI)
Design a CI/CD platform for 100K orgs and 10M workflow runs/day: YAML DAG execution, ephemeral runner pools (Firecracker), content-addressed artifacts, dependency caches, secrets injection, and multi-tenant isolation at 40K concurrent runners.
KafkaS3PostgreSQL+1 - 8.52
Observability Platform (Datadog / New Relic / Honeycomb)
Design a unified observability platform for 10M hosts and 1B events/sec: OTLP ingestion across metrics, logs, and traces, cardinality control, trace-log correlation, multi-tenant isolation, and query latency at 100K concurrent analysts.
PrometheusGrafanaOpenTelemetry+5 - 8.53
Search Engine (Google-Scale / Brave Search)
Design a web-scale search engine over 10B documents serving 100K queries/sec at <200 ms p99: sharded inverted index, BM25 + PageRank + neural re-ranking cascade, query understanding, and freshness pipelines.
ElasticsearchKafkaBigtable+3 - 8.54
Brokerage Platform (Robinhood / E*TRADE / Interactive Brokers)
Design a retail brokerage for 30M users: order routing, symbol-channel quote fanout, fractional-share aggregation, tax-lot accounting, and seven-year regulatory audit.
PostgreSQLKafkaRedis+4 - 8.55
Channel-Scale Chat (Discord / Slack)
Design channel-scale chat for 100K+ member channels with pub/sub fanout, RBAC on the hot path, presence aggregation, and workspace search.
ScyllaDBCassandraRedis+6
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