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Lessons (40)

• Domain-Driven Design: Strategic Design

  … Ideally they line up one-to-one, but not always, especially in legacy systems. Bounded contexts are the …

• C4 Architecture Diagrams: Context, Container, Component and Code

  … C4 system-context diagram What to include Include only: 1. People who use the system. 2. One box …

• Prompting and Structured Outputs

  Write clear instructions, provide context and examples, constrain responses, and validate model output in code. The big idea …

• Go Concurrency: Goroutines, Channels and Context

  … limit how much runs at once go func process(ctx context.Context, jobs []Job, workers int) []Result { jobCh …

• Putting AI Systems into Production

  … feature is a software system around a model: input validation, retrieval or context, provider calls, output checks, user …

• What Is Software Architecture?

  … Context The system, its users and external systems Everyone 2. Container Apps, databases, queues inside the system Developers …

• Kubernetes Cluster Architecture, Simply

  … kubectl config current-context Which cluster/context will commands use? Always check the current context before changing anything …

• Choosing an Architecture

  … system shape , code organisation , domain modelling . Answer each. - The safest default: a modular monolith along DDD bounded contexts …

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

  … Include event ID, schema version, ordering key and trace context; consumers deduplicate and send exhausted failures to a …

• React Hooks in Practice

  … Context makes a value available to a whole subtree. jsx const ThemeContext = createContext("light"); function App() { const [theme …

• Design a Reliable Notification System

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

• System Design Interview Framework

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

• Backend Languages: Node.js, Go, Python & Rust

  … users/:id", func(c gin.Context) { user, err := findUser(c.Request.Context(), c.Param("id")) if err != nil …

• Architecture Patterns at Scale

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

• Observability: Logs, Metrics & Traces

  … hard to search, no context console.log("Payment failed for user 42"); // ✅ Structured (pino): every field is searchable …

• Data Structures for Scale

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

• Behavioral Patterns I: Observer, Strategy, Command, State

  … add a new strategy, don't edit the context. --- 3. Command 🧾 Analogy: A waiter writes your order …

• Design a Social Media Feed

  … Most large systems use a hybrid. Keep likes/comments as separate scalable counters or event streams. It is …

• Capacity, Availability, Latency and CAP

  … load, response time, uptime and partition-time policy. The problem in context A retailer serves 20 million reads …

• The L6 System-Design Thinking Loop

  … define correctness, size the load, design failure paths, and measure recovery. The problem in context A concert releases …

• Batch vs Stream and Data Modeling

  … deliberately denormalize proven read bottlenecks. The problem in context A marketplace needs yesterday’s financial report and a …

• Big Data: ETL, Warehouses and Streaming

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

• AI Specialties and Real-World Examples

  … robot Environments, rewards, exploration, policy evaluation Generative systems Prompt or context → new content Draft an explanation or product …

• Design a Polite Web Crawler

  … normalize, deduplicate and schedule per host. The problem in context A search product wants to crawl 100 million …

• Design an E-Commerce Checkout

  … inventory reservation, idempotent payment, order creation and durable events. The problem in context A buyer orders the last …

• Storage, Search and Location Queries

  Use the right data system for files, text search and nearby-place queries instead of forcing every need …

• Releases, Observability and Production Safety

  … CI validates an immutable artifact, controlled rollout observes SLOs, and a rollback path limits blast radius](/img/system …

• Time, Consistency and Distributed Transactions

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

• Design a Logging and Monitoring Platform

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

• Distributed Coordination: Consensus, Heartbeats and Gossip

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

• Design a File Storage Service

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

• Proxies, APIs and Real-Time Protocols

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

• Networking, DNS and Traffic Routing

  … balancers, anycast and reverse proxies. The problem in context Customers in Dhaka and London reach the same API …

• Database Internals, Replication and Scaling

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

• API Contracts, Gateways and Security

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

• Caching, Consistent Hashing and Sharding

  … cache and database consistency costs. The problem in context A product catalog has 100,000 reads/s, but …

• Design a URL Shortener

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

• Multi-Region and Disaster Recovery

  … food order system Orders must not disappear, but the restaurant discovery feed can temporarily show stale results. Data …

• Flash Sale: 10 Million Buyers, No Oversell

  … The durable inventory owner decides the winner atomically. The problem in context A store has 1,000 discounted …

• Design a Ride-Sharing Service

  … a geo index finds candidates, an atomic assignment leases a driver, and live updates flow separately](/img/system …