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Lessons (40)

• Event-Driven Architecture

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

• CQRS & Event Sourcing

  … save state every N events, then replay only newer events Event schemas change over time Versioned events, upcasters …

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

  Choose the right push or event mechanism and keep event delivery observable, idempotent and replayable. ![Event patterns: an …

• Service Communication: Sync vs Async

  Should services call each other directly or talk through events? Compare request/response with messaging, orchestration with choreography …

• JavaScript Essentials: Event Loop, Closures & this

  … Visual explanations of the event loop, microtasks, closures, and how 'this' is decided. Part 1: The event loop …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … Pick what<br/ your team can operate well"] ✅ Kafka shines for: event-driven microservices where many services react …

• Architecture Patterns at Scale

  Choose client-server, microservices, serverless, event-driven or peer-to-peer architecture based on ownership, failure boundaries and …

• What Is Apache Kafka?

  Kafka is a distributed, durable log of events that many systems can write to and read from at …

• Serverless Architecture

  … create a thumbnail export const handler = async (event: S3Event) = { for (const record of event.Records) { const image = await …

• Data in Microservices: Sagas & the Outbox Pattern

  … Design compensations as business actions . Choreography saga (events) Each service listens for events and reacts. No central coordinator …

• Domain-Driven Design: Tactical Patterns

  … DomainEvent[] { const e = this.events; this.events = []; return e; } private assertDraft() { if (this.status !== "DRAFT") throw new DomainError …

• Finding Service Boundaries with DDD

  … 6. Event storming: put business experts and developers in a room with sticky notes for every domain event …

• Choosing an Architecture

  … vertical slices (mostly CRUD)"] c1[search slice] c2[update price slice] end Ord -.- OrderPlaced, in-process event Bill …

• Design an E-Commerce Checkout

  … inventory reservation, idempotent payment, order creation and durable events. ![Checkout: catalog/search are read paths while inventory, payment …

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

  … class EventEmitter { listeners = new Map(); on(event, listener) { if (!this. listeners.has(event)) this. listeners.set(event, new …

• Domain-Driven Design: Strategic Design

  … Domains and subdomains, ubiquitous language, bounded contexts, all the context-mapping patterns, and event storming to discover them …

• Design a Chat Application

  … Offline push comes from the durable event, not an in-memory gateway.

• Big Data: ETL, Warehouses and Streaming

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

• Design a Social Media Feed

  Build a fast home feed with fan-out choices, durable post storage, eventual consistency and safeguards for celebrity …

• Delivery Guarantees: At-Most, At-Least & Exactly Once

  … remember processed event IDs (same transaction as the business change) await db.transaction(async (tx) = { const inserted = await …

• Vertical Slice Architecture & the Modular Monolith

  … OrderRepository; events: EventBus }, cmd: PlaceOrderCommand) { const order = Order.create(cmd.customerId, cmd.lines); // business rules in the domain …

• Time, Consistency and Distributed Transactions

  … each local transaction emits an event and has a defined compensation. An outbox writes business state and its …

• Topics, Partitions & Offsets

  … A topic is a named stream of related events: orders , payments , page-views , user-signups . bash kafka-topics …

• Kafka Producers

  … order.totalCents }), headers: { eventType: "OrderPlaced", eventId: crypto.randomUUID(), schemaVersion: "1" }, }, ], }); } process.on("SIGTERM", async () = { await producer.disconnect(); // flush …

• Observability: Logs, Metrics & Traces

  … The car's black box records every event ( logs ). And if you tracked one trip across the city …

• Indexes, EXPLAIN & Query Plans

  … email) with unique/partial rule Time-range events per tenant events(tenant id, created at) Deep cursor page …

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

  … one thread + event loop"] EL(("🔁 event loop")) -- IO1[DB call → wait in background] EL -- IO2[HTTP call → wait …

• Which Pattern Do I Need?

  … 4. 🏨 Facade — service layers and SDKs 5. 📰 Observer — events everywhere, UI and backend 6. 🗺️ Strategy — pluggable algorithms …

• Consumers & Consumer Groups

  … async ({ topic, partition, message }) = { const eventId = message.headers.eventId.toString(); if (!(await processedEvents.has(eventId))) { // idempotency check await …

• What Is Software Architecture?

  … inside an app (Layered, Clean, Hexagonal, Onion), the domain (DDD), and the whole system (microservices, event-driven, serverless …

• Helm, kubectl Cheat Sheet & Best Practices

  … kubectl top pods / kubectl top nodes Recent events kubectl get events --sort-by=.lastTimestamp Dry run + diff kubectl …

• Design a Ride-Sharing Service

  … Locations are eventually consistent; ride assignment needs stronger ownership. Watch stale-location age, match latency, conflicts and regional …

• Design a File Storage Service

  … On completion validate checksums, commit metadata, and emit a versioned change event. Concern Design choice --- --- Unstable large upload …

• Batch vs Stream and Data Modeling

  … Batch runs a bounded set later; streaming handles events continuously while data modeling controls read and write cost …

• Distributed Coordination: Consensus, Heartbeats and Gossip

  … Suspicion, not certainty Spread membership at scale Gossip Eventual convergence Was data corrupted? Checksum Detect accidental modification Raft …

• React Fundamentals

  … ProductCard] PC1 -.- "onAdd(id) ⬆ events go up" App Data flows down (props); events flow up (callbacks). This one …

• Proxies, APIs and Real-Time Protocols

  … call gRPC/RPC Tighter coupling Slow work Queue Eventual result and lag Occasional updates Long polling Repeated connections …

• Pods

  … get events --sort-by=.lastTimestamp mermaid flowchart TD P{Pod not healthy?} -- Pending D1["describe → events:<br/ 'Insufficient …

• Deploying & Operating Microservices

  … Other services depend on your API and your events. Changes must be backward compatible . ✅ Safe (additive) ❌ Breaking --- --- Add …

• Views, Triggers & Stored Procedures

  … A trigger runs automatically from an event. Transaction-control and return-value capabilities vary by engine, so name …