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Lessons (40)

• Design a File Storage Service

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

• System Design Interview Framework

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

• 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 Chat Application

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

• 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

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

• 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 Reliable Notification System

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

• Design a Logging and Monitoring Platform

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

• Design a Social Media Feed

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

• What Are Design Patterns?

  Design patterns are named, reusable solutions to problems that keep coming up in software design. Meet the three …

• Domain-Driven Design: Strategic Design

  … DDD has two halves: Strategic design (this lesson) Tactical design (next lesson) --- --- --- Zoom level The whole business and …

• DBMS Foundations, Keys & Normalization

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

• Capacity, Availability, Latency and CAP

  The constraints that shape every distributed design: load, response time, uptime and partition-time policy. Start with numbers …

• REST API Design

  Design APIs that are predictable and pleasant to use: resource naming, methods, status codes, pagination, versioning, errors and …

• Domain-Driven Design: Tactical Patterns

  … customerId only The four rules of aggregate design (Vaughn Vernon) Rule Why --- --- 1. Protect invariants inside the boundary …

• What Is Software Architecture?

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

• Caching, Consistent Hashing and Sharding

  … TTL, invalidation and request coalescing are part of the design. A hash ring moves only some keys when …

• Finding Service Boundaries with DDD

  … For the full picture, see [DDD strategic design](/learn/software-architecture/ddd-strategic-design) and [DDD tactical patterns …

• Indexes, EXPLAIN & Query Plans

  Design indexes from real filter, join and sort patterns, then prove improvements with query plans and production-like …

• Event-Driven Architecture

  … Broker vs mediator topologies, the four kinds of event patterns, event design, and the real trade-offs. The …

• Batch vs Stream and Data Modeling

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

• 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

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

• 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 …

• 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

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

• 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

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

• 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 …

• Microkernel (Plugin) Architecture

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

• 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 …

• Scaling, Load Balancing & Rate Limiting

  … More servers Simplicity ✅ No code changes Needs stateless design Limit Hardware ceiling, expensive at the top Practically unlimited …

• 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

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

• Which Pattern Do I Need?

  A problem-first guide for picking the right design pattern, telling look-alike patterns apart, and spotting when …