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Lessons (40)

• Design a Logging and Monitoring Platform

  … l6/telemetry-platform.svg) Agents batch and compress logs, metrics and traces to an authenticated ingestion gateway. A …

• Observability: Logs, Metrics & Traces

  … Logs, the "why" A log is a timestamped record of an event. Write structured logs (JSON), not free …

• MVC, MVP & MVVM

  Three patterns for separating what the user sees from the data and logic behind it. How each works …

• Sorting Algorithms

  … beating n log n Comparison sorts can't beat O(n log n). But if values are small …

• JavaScript Essentials: Event Loop, Closures & this

  … run all microtasks, then one task The famous quiz js console.log("1"); setTimeout(() = console.log("2"), 0 …

• Big-O Notation Made Simple

  … O(1), O(log n), O(n), O(n log n), O(n²). The steepest curve explodes fastest …

• Authentication, Authorization & API Security

  … Click "Log in with Google" App- U: redirect to Google (+ PKCE challenge) U- G: log in + consent G …

• Pods

  … writes logs to /var/log"] -- Vol[("shared volume")] Vol -- Side["📤 log-shipper sidecar<br/ sends logs to Loki …

• What Is Apache Kafka?

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

• Heaps & Priority Queues

  … Swap with the smaller child"] -- c c -- No e["✅ Return saved min"] The tree's height is log …

• DSA Interview Patterns Cheat Sheet

  … O(1) O(n) O(log n) O(log n) \ O(1) at the end · \ \ when you already …

• Frontend Testing Strategy

  … pure logic Best for pure functions: formatters, calculations, validation, reducers. ts // cart.ts export function cartTotal(items: { price …

• Helm, kubectl Cheat Sheet & Best Practices

  … team-shop } rules: - apiGroups: [""] resources: ["pods", "pods/log"] verbs: ["get", "list", "watch"] --- apiVersion: rbac.authorization.k8s.io/v1 …

• Structural Patterns: How to Connect Objects

  … Date.now() }); } } const logger = new WinstonAdapter(winston); // the rest of the app is unchanged logger.log("info", "Server …

• D — Dependency Inversion Principle

  High-level business logic should depend on abstractions, not on concrete details like databases or email providers. The …

• Distributed Coordination: Consensus, Heartbeats and Gossip

  … coordination.svg) Problem Tool Guarantee --- --- --- One ordered configuration/log Raft or Paxos-style consensus Majority agreement Is a …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … RabbitMQ routes and deletes; Kafka stores an ordered log you can replay](/img/kafka/kafka-vs-rabbit.svg …

• Layered (N-Tier) Architecture

  … Keep most layers closed, or the separation quickly erodes. Layers vs tiers - Layers are a logical split of …

• Database Internals, Replication and Scaling

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

• Choosing an Architecture

  … a modular monolith along DDD bounded contexts , Hexagonal/Clean where logic is rich, simpler slices where it isn …

• Docker & Containers

  … docker run -d -p 3000:3000 --name api -e DATABASE URL=postgres://… shop-api:1.0 docker logs …

• Creational Patterns: How to Make Objects

  … 2 }); console.log(tank.describe()); // Tank: ❤️ 400, 🏃 2 📘 JavaScript itself is prototype-based : every object links to a …

• Clean Error Handling

  … logged, then forgotten; the caller thinks it worked try { await saveOrder(order); } catch (e) { console.log(e); } js …

• Storage Engines & Database Operations

  Understand B-trees, LSM trees, write-ahead logs, connection pools, backups and the signals behind database reliability. What …

• N+1 Queries, Loading & Pagination

  … In development, log duplicate query fingerprints. In production, sample traces rather than logging sensitive SQL values.

• ConfigMaps, Secrets & Storage

  … env var env: - name: LOG LEVEL valueFrom: configMapKeyRef: { name: shop-api-config, key: LOG LEVEL } a single key …

• Which Pattern Do I Need?

  … an object wrapping another"] W[Wrapper] -- O[Original] end Same -- D["Decorator:<br/ 'I add logging'"] Same -- P …

• Topics, Partitions & Offsets

  … the unit of parallelism Each partition is an ordered, append-only log stored on one broker (plus copies …

• Serverless Architecture

  … invest in structured logs, tracing (X-Ray / OpenTelemetry) Cost at sustained high load Containers or VMs can be …

• Onion Architecture & Clean vs Hexagonal vs Onion

  … All three share the same rule: 🎯 The business logic is at the centre and depends on nothing. Infrastructure …

• Hexagonal Architecture (Ports & Adapters)

  … string[]) { const loan = await borrowing.borrow(memberId, bookId); console.log( ✅ Borrowed ${bookId}, due ${loan.dueDate.toDateString()} ); } 3. Driven …

• React Hooks in Practice

  … reuse logic Any function starting with use that calls other hooks is a custom hook. It's the …

• Releases, Observability and Production Safety

  … Correlate logs, metrics and traces with request IDs; alert on SLO burn, not noise. Protect traffic with TLS …

• Behavioral Patterns II: Chain, Template, Iterator, Mediator, Memento, Visitor

  … 2500 }); // "👔 manager approved" mermaid flowchart LR R[Request] -- H1[Logger] -- H2[Rate limiter] -- H3[Auth] -- H4[Route handler …

• Big Data: ETL, Warehouses and Streaming

  … as the main source and reprocesses it when logic changes. Choose based on team operations and freshness needs …

• API Contracts, Gateways and Security

  … Use TLS, rate limits, audit logs and secrets management.

• Proxies, APIs and Real-Time Protocols

  … A queue is not a WebSocket, and a WebSocket is not a durable message log.

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

  … Publish committed database changes Use an outbox/transaction log, not app guesses Delivery is usually at-least-once …

• Trees & Binary Search Trees

  … Shape Bushy, height ≈ log n A long chain, height = n Search / insert O(log n) O(n) 😢 How …

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

  … The request became an object . Problem: you want to queue, log, undo or redo operations. js class TextEditor …