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HLD-201 — High-Throughput URL Shortener & Redirector
HLD-101 — Distributed API Rate Limiter & Quota Gateway
HLD-301 — Flash-Sale Concert Ticket Checkout
HLD-223 — Adaptive Bitrate Video Streaming & Edge Manifest CDN
HLD-102 — Pastebin & Ephemeral Text Snippet Store
HLD-402 — Global Real-Time Social Timeline Feed
HLD-202 — Product Catalog & Autocomplete Typeahead Search
HLD-310 — 1-on-1 & Small-Group E2EE Messaging, Offline Queue & Receipts
HLD-107 — Distributed 64-Bit ID & Sequence Service
HLD-221 — Online Coding Judge & Sandbox Execution Queue
HLD-319 — Global Card Payment Authorization & Idempotent Retry Engine
HLD-103 — Global Feature Flag & Dynamic Config Service
HLD-303 — Real-Time Ride-Hail Driver Location & Dispatch
HLD-401 — Low-Latency Equity Order Gateway & Risk Pre-Check
HLD-117 — Live Webinar Poll & Audience Vote Tally Service
HLD-216 — Flight & Retail Price-Drop Watchlist Matcher
HLD-320 — Sub-40ms Live Stock Quote Snapshot & WebSocket Ticker Feed
HLD-124 — Perceptual Image Hash & Blocklist Moderation API
HLD-236 — Skill-Based Live Support Ticket & SLA Queue Router
HLD-404 — Idempotent Payment Ledger & Double-Entry Wallet
HLD-304 — Real-Time Ad Click Attribution & Budget Pacing
HLD-224 — Real-Time Top-K Trending Topics & Bestsellers Engine
HLD-130 — Dynamic i18n String Bundle & Live Localization API
HLD-235 — Cloud Photo Backup, Dedup & Timeline Album Service
HLD-325 — Inline Low-Latency LLM Prompt-Injection & Guardrails Gateway
HLD-121 — Microservice Health-Check & Service Discovery Registry
HLD-407 — Global Multiplayer Document Revision Log & OT/CRDT Sequencer
HLD-227 — Geo-Sharded Dating Deck & Mutual Swipe Matcher
HLD-218 — CI/CD Pipeline Queue & Ephemeral Runner Dispatcher
HLD-127 — E-Commerce Promo Code & Eligibility Rule Validator
HLD-317 — Multiplayer Infinite Canvas & CRDT Vector Sync (Figma/Miro)
HLD-206 — Cloud Metrics & Alerting Time-Series Store
HLD-114 — SMS & Email One-Time Passcode (OTP) Verifier
HLD-409 — Planet-Scale Web Search Inverted Index & Query Aggregator
HLD-204 — Viral News Article Comment Thread Backend
HLD-128 — Real-Time Phishing & Safe-Browsing URL Reputation API
HLD-302 — Global Hotel Room Inventory & Overbooking Guard
HLD-208 — Cross-Device Video & Podcast Resume Sync
HLD-115 — Edge Geo-IP Country & Timezone Lookup Service
HLD-318 — Live Road-Segment Traffic Telemetry & Partitioned ETA Engine
HLD-203 — Distributed Delayed Job & Cron Scheduler
HLD-405 — Multi-Tenant Distributed Lock & Lease Coordinator
HLD-123 — Mobile APNs / FCM Device Token & Topic Registry
HLD-205 — Global Session & Auth Token Verification Store
HLD-306 — Cloud Drive File Metadata & Delta Sync Engine
HLD-113 — Immutable Enterprise Compliance Audit Log Sink
HLD-212 — Social Follow Graph & Blocklist Lookup Service
HLD-410 — Real-Time Bidding (RTB) Ad Exchange & 45ms Budget Pacer
HLD-321 — Global Video Conferencing Room Signaling & SFU Topology
HLD-226 — Enterprise Calendar Scheduling, Recurrence & Sync
HLD-118 — Chat URL OpenGraph Metadata & Preview Cache
HLD-231 — Enterprise RAG Document Chunking & Hybrid Vector Search
HLD-323 — High-Concurrency Timed Online Auction & Sniping Guard
HLD-129 — Global Podcast RSS Episode Catalog & Update Notifier
HLD-415 — Global Election & Olympics Live Scoreboard (300k-RPS Edge Feed)
HLD-229 — Distributed Tracing Span Collector & Tail Sampler
HLD-217 — Sticky A/B Experiment Assignment & Exposure Log
HLD-105 — Image Upload & Multi-Resolution Thumbnail CDN
HLD-307 — Live Gaming Leaderboard & Rank Aggregator
HLD-232 — Multi-Warehouse Retail Inventory & Delivery Promise API
HLD-120 — Global Anycast Authoritative DNS & Zone Store
HLD-414 — Anycast L7 WAF, Bot Reputation & Global Token-Bucket Edge
HLD-222 — Reddit-Style Nested Comment Tree & Hot-Rank Votes
HLD-125 — Static Site Atomic Deployment & Edge Asset Router
HLD-315 — Short-Video Multi-Stage Recall, Watch-Signal & Feed Ranker
HLD-220 — Connected Vehicle OTA Firmware Rollout Manifests
HLD-108 — Event QR Badge Lookup & Gate Check-In API
HLD-322 — Sharded HNSW Vector Database & Metadata Filter Engine
HLD-230 — Priority Multi-Channel Notification Router (Push/SMS/Email)
HLD-406 — Partitioned Quorum Key-Value Store (Dynamo / Cassandra)
HLD-122 — Multi-Tenant Secrets & Envelope Encryption Vault
HLD-207 — Live Food Delivery Order & Courier Status
HLD-308 — Multiplayer Document Cursor & Operation Relay
HLD-119 — Distributed Cache Proxy & Consistent Hashing Router
HLD-233 — Smart Airport & Stadium Garage Spot Reservation Service
HLD-413 — High-Frequency Crypto Margin Engine & Hot-Wallet Settlement
HLD-311 — 10M-Concurrent User Presence Heartbeat & Guild Fan-Out
HLD-237 — Personalized Music Home Shelf & Real-Time Skip Feedback
HLD-112 — Global Currency FX Exchange Rate Ticker API
HLD-211 — SaaS Usage-Based API Metering & Spend Aggregator
HLD-314 — ChatGPT-Scale Conversational Assistant, Context & SSE Gateway
HLD-104 — Webhook & Transactional Notification Dispatcher
HLD-403 — 10M-Viewer Live Sports Broadcast Chat & Reactions
HLD-215 — In-App Notification Inbox & Unread Badge Store
HLD-225 — Centralized Log Ingestion & Full-Text Search Pipeline
HLD-126 — Calendar Free/Busy Slot Lookup & Booking Link API
HLD-313 — Partitioned Commit-Log Message Queue & Offset Coordinator
HLD-234 — Real-Time Stock & Crypto Price Threshold Alert Matcher
HLD-109 — Container & NPM Package Tarball Registry Mirror
HLD-408 — Multi-Cluster LLM Prefix KV-Cache Router & Token Scheduler
HLD-239 — Global Airline Fare Cache & Multi-Leg Search Aggregator
HLD-116 — Mobile App Crash Dump & Stack-Trace Collector
HLD-309 — Inline Card Payment Fraud & Velocity Feature Store
HLD-213 — Video Upload & Multi-Bitrate HLS Transcode Queue
HLD-111 — User Profile Card & Avatar Metadata Service
HLD-312 — Geo-Indexed Vacation Rental Search & Date-Range Lock Engine
HLD-228 — Live "Nearby Friends" Geohash Proximity Radar
HLD-411 — Geo-Partitioned Distributed SQL & Serializable Transaction Engine
HLD-106 — IoT Smart-Meter Telemetry Ingestion Pipeline
HLD-214 — Nearby Restaurant & Local Business Geo-Search
HLD-316 — S3-Scale Multipart Blob Metadata & Placement Index
HLD-110 — Transactional Email Bounce & Suppression Store
HLD-240 — Spatial Supply-Demand Window & Dynamic Surge Pricing
HLD-412 — Durable Stateful AI Agent Checkpointing & Sandboxed Tool Runner
HLD-305 — Real-Time Group Chat & Channel Persistence
HLD-238 — Real-Time Product Clickstream & Funnel Analytics Store
HLD-210 — E-Commerce Persistent Shopping Cart Backend
HLD-219 — Collaborative Music Playlist & Synced Lyrics Store
HLD-324 — Three-Sided Food Delivery State Machine & Dasher Offer Lock
HLD-209 — Distributed Web Crawler URL Frontier & Dedup
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