⏱ 8 min read Introduction Geospatial indexing enables efficient proximity queries — find all restaurants within 2km — over large datasets of lat/lng coordinates. […] Read article

⏱ 7 min read Introduction Consensus algorithms allow a cluster of nodes to agree on a sequence of values despite node failures. They are Read article

⏱ 9 min read Introduction Metrics collection is the foundation of system observability. The four core metric types cover most monitoring needs: a counter Read article

⏱ 8 min read Introduction Real-time analytics surfaces business metrics such as DAU, revenue, and conversion rates with sub-second query latency on continuously updating Read article

⏱ 8 min read Introduction Authentication services verify who the user is; authorization services control what they can do. A centralized auth service handles Read article

⏱ 8 min read Introduction Polling systems must ensure one vote per eligible voter, prevent fraud, aggregate results in real time, and optionally preserve Read article

⏱ 9 min read Introduction Electronic Health Record systems store and exchange patient health data across providers, payers, and patients. Design must prioritize data Read article

⏱ 8 min read Introduction Logistics tracking systems process millions of scan events daily, maintain accurate package state, and surface real-time location to customers. Read article

⏱ 7 min read Multiplayer game servers synchronize game state across all players in a session with minimal latency. The design must handle packet Read article

⏱ 7 min read IoT platforms ingest telemetry from millions of devices with high write throughput, store time-series data efficiently, and enable real-time alerting Read article

⏱ 8 min read Airport management systems orchestrate hundreds of daily flight operations including gate assignment, ground handling, baggage routing, and passenger information display. Read article

⏱ 8 min read ATM networks process card transactions across millions of terminals through authorization switches. The design must be highly available, idempotent, and Read article

⏱ 9 min read Introduction KYC (Know Your Customer) requires verifying user identity using government-issued documents. It is a regulatory requirement for fintech companies, Read article

⏱ 11 min read Real-time traffic routing is one of the canonical systems design problems — and also one of the most algorithm-heavy LLD Read article

⏱ 10 min read Autonomous vehicle fleet management sits at the intersection of real-time embedded systems, cloud infrastructure, and safety-critical engineering. This LLD covers Read article