Search

Lessons (40)

• System Design Interview Framework

  … clarify requirements, estimate scale, draw the core path, then deep dive into risks and recovery](/img/system-design …

• Design a Reliable Notification System

  … preferences feed priority queues, channel providers and idempotent delivery tracking](/img/system-design-l6/notifications.svg) Create an …

• The L6 System-Design Thinking Loop

  … invariant first, then scale, failure, recovery and blast radius](/img/system-design-l6/design-loop.svg) Five questions …

• Design a Social Media Feed

  … on read behind a cached timeline API](/img/system-design-l6/social-feed.svg) Posts are durable objects …

• Design a File Storage Service

  … multipart uploads go to object storage; the API owns metadata, sharing and versioned changes](/img/system-design-l6 …

• Design a Chat Application

  … fan-out, presence and offline push paths](/img/system-design-l6/chat.svg) Persist a message before acknowledging …

• Design a URL Shortener

  … durable mappings, cache-backed redirects and asynchronous analytics](/img/system-design-l6/url-shortener.svg) Generate a Base62 …

• Design a Ride-Sharing Service

  … a driver, and live updates flow separately](/img/system-design-l6/ride-sharing.svg) A driver must not …

• Design a Polite Web Crawler

  … a URL frontier schedules polite fetches while deduplication and storage process discovered links](/img/system-design-l6/web …

• Design an E-Commerce Checkout

  … catalog/search are read paths while inventory, payment and order transitions are owned and idempotent](/img/system-design …

• Design a Logging and Monitoring Platform

  … agents batch into an ingestion layer, durable streams feed hot search, metrics and cold archival](/img/system-design …

• Domain-Driven Design: Strategic Design

  … halves: Strategic design (this lesson) Tactical design (next lesson) --- --- --- Zoom level The whole business and system Code inside …

• What Is Software Architecture?

  … Whatever that is." (Ralph Johnson) 📘 "Architecture represents the significant design decisions that shape a system, where significant is …

• Capacity, Availability, Latency and CAP

  … a design chooses latency targets, availability targets and a partition-time consistency policy](/img/system-design-l6/capacity …

• DBMS Foundations, Keys & Normalization

  Detailed interview answers for DBMS advantages, normalization, keys, abstraction and conceptual design. Covers PDF questions 1-5, 12 …

• Caching, Consistent Hashing and Sharding

  … stable placement, and shards for database scale](/img/system-design-l6/data-distribution.svg) Tool Solves Risk --- --- --- Cache …

• Event-Driven Architecture

  Build systems where components react to events instead of calling each other. Broker vs mediator topologies, the four …

• Microkernel (Plugin) Architecture

  … How VS Code, browsers, Webpack and ESLint are built, how to design a plug-in contract, and the …

• Batch vs Stream and Data Modeling

  … data modeling controls read and write cost](/img/system-design-l6/batch-stream.svg) Choice Use when Cost …

• Architecture Patterns at Scale

  … central services, independently deployed services, event functions and decentralized peers](/img/system-design-l6/architecture-patterns.svg) Style …

• Releases, Observability and Production Safety

  … and a rollback path limits blast radius](/img/system-design-l6/release-operations.svg) Tool Purpose --- --- Rolling rollout …

• Distributed Coordination: Consensus, Heartbeats and Gossip

  … leader agreement, heartbeats, gossip membership and checksums solve different failure questions](/img/system-design-l6/coordination.svg) Problem …

• Big Data: ETL, Warehouses and Streaming

  … raw events land durably, ETL/stream processing creates curated lake and warehouse datasets](/img/system-design-l6/big …

• Which Pattern Do I Need?

  … have. Patterns at system scale The same ideas reappear when you design whole systems, which you'll meet …

• API Contracts, Gateways and Security

  … a gateway applies authentication, authorization, rate limits and routing before services enforce resource-level policy](/img/system-design …

• Proxies, APIs and Real-Time Protocols

  … reverse proxy at the edge, request APIs, queues and persistent real-time connections](/img/system-design-l6/protocols …

• Real-Time, Pub/Sub, Webhooks and CDC

  … server-sent updates and database change capture](/img/system-design-l6/realtime-events.svg) Pattern Best for Key …

• Data Structures for Scale

  … spatial indexes locate nearby items; probabilistic sketches answer large-set questions cheaply](/img/system-design-l6/scale-data …

• Networking, DNS and Traffic Routing

  … and load balancer choose a healthy service](/img/system-design-l6/network-routing.svg) The OSI model is …

• Database Internals, Replication and Scaling

  … writes become durable log records, replicas serve compatible reads, and pools protect scarce connections](/img/system-design-l6 …

• Time, Consistency and Distributed Transactions

  … clocks order observations, fencing protects ownership, and sagas compensate cross-service work](/img/system-design-l6/time-transactions …

• Flash Sale: 10 Million Buyers, No Oversell

  … queueing controls traffic while the inventory owner atomically reserves the unit](/img/system-design-l6/flash-sale.svg …

• Monolith vs Microservices

  … service makes everything slow". Conway's Law 📘 "Organisations design systems that mirror their own communication structure." (Melvin Conway …

• Timeouts, Retries & Backpressure

  … deadline budgets, limited concurrency, a queue and explicit overload shedding](/img/system-design-l6/backpressure.svg) One deadline …

• Debug Latency Like an Investigator

  … pool wait, database waits and downstream services](/img/system-design-l6/latency-investigation.svg) Symptom Test first --- --- p50 …

• Exactly-Once Payment Processing

  … durable attempt, provider idempotency key, then recovery for an unknown result](/img/system-design-l6/payment-idempotency.svg …

• Premiere-Night Video Streaming

  … plane with edge, regional and origin tiers](/img/system-design-l6/premiere-streaming.svg) Plane Handles Goal --- --- --- Control …

• Choosing an Architecture

  … route traffic piece by piece to the new system Replace legacy systems without a big-bang rewrite mermaid …

• SQL vs NoSQL Databases

  … scale UP"] V1[Server] -- V2["Bigger server 💪<br/ more CPU/RAM"] end subgraph Horizontal["NoSQL by design: scale …

• Resilience Patterns

  In a distributed system something is always failing. Timeouts, retries with backoff, circuit breakers, bulkheads, fallbacks and rate …