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Lessons (40)

• What Are Design Patterns?

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

• Which Pattern Do I Need?

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

• Architecture Patterns at Scale

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

• DSA Interview Patterns Cheat Sheet

  … Interviews test whether you can recognise the pattern from the wording, then apply its template. Pick a technique …

• Creational Patterns: How to Make Objects

  … Creational patterns hide the "how" of creating objects , so the rest of the code only asks for what …

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

  The four behavioral patterns you'll use most, explained with everyday analogies, diagrams and practical JavaScript. Why behavioral …

• Data in Microservices: Sagas & the Outbox Pattern

  … So microservices accept eventual consistency and use sagas. The saga pattern A saga is a series of local …

• Structural Patterns: How to Connect Objects

  … How to plug incompatible pieces together and build big structures from small ones. Why structural patterns? Structural patterns …

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

  Six more behavioral patterns, from Express-style middleware chains to undo snapshots, each with a picture and a …

• Resilience Patterns

  … The patterns below stop that.  1. Timeouts: never wait forever …

• Domain-Driven Design: Tactical Patterns

  … small, immutable, self-validating ⭐ Value objects are the easiest tactical pattern to adopt, and remove a huge class …

• Hash Maps & Sets

  … Learn how hashing gives O(1) lookups, how collisions are handled, and the patterns (counting, seen-set, grouping …

• 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 …

• Event-Driven Architecture

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

• Indexes, EXPLAIN & Query Plans

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

• MVC, MVP & MVVM

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

• Database Internals, Replication and Scaling

  … Choose database types by access pattern: relational, document, key-value, wide-column, graph, time-series, search and vector …

• DRY: Don't Repeat Yourself

  … email.js const EMAIL PATTERN = /^[^@\s]+@[^@\s]+\.[^@\s]+$/; export const isValidEmail = (email) = EMAIL PATTERN.test(email); // everywhere else …

• Heaps & Priority Queues

  … For objects: (a, b) = a.priority - b.priority . Pattern: Top K ⭐ "Find the k largest numbers in a …

• What Is Software Architecture?

  … High Design How is one part organised? Classes, patterns (Strategy, Repository), module APIs 🟡 Medium Code How is …

• CQRS & Event Sourcing

  … Powerful patterns, explained simply, with honest trade-offs. Part 1: CQRS The big idea A restaurant kitchen and …

• Scaling, Load Balancing & Rate Limiting

  … Design for it: Pattern Purpose --- --- Timeouts Never wait forever on a dependency Retries with exponential backoff + jitter Survive …

• Domain-Driven Design: Strategic Design

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

• KISS: Keep It Simple, Stupid

  … welcomeTemplate(user) }); } When you have five notification channels, a strategy pattern may earn its place. With one, it …

• React vs Vue vs Angular

  … Simple mental model; sometimes needs memoisation. - Vue wraps state in Proxies (remember the Proxy pattern?) and tracks exactly …

• Pods

  … network, provided by the CNI plugin). Multi-container patterns Sidecar A helper container that extends the main one …

• State Management (Redux, Zustand, TanStack Query)

  … Redux Toolkit (structured) Redux is the classic, predictable pattern: one store , state changed only by dispatching actions handled …

• Service Communication: Sync vs Async

  … All covered in Resilience Patterns . Avoid chatty services mermaid flowchart LR subgraph Chatty["❌ Chatty: N+1 over the …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … the easiest way to implement the outbox pattern or to stream database changes to search indexes and warehouses …

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

  … data). Choosing a guarantee Guarantee Producer config Consumer pattern Use for --- --- --- --- At-most-once acks=0 or 1 …

• SQL vs NoSQL Databases

  … Queries are varied and change over time Access patterns are known and simple Data integrity matters most Schema …

• Kafka Producers

  … close the producer on shutdown - [ ] Use the outbox pattern when writing to a database and Kafka together (see …

• Microkernel (Plugin) Architecture

  … plugins: [react()] Convention Load everything matching a naming pattern or folder eslint-plugin- , a plugins/ folder Manifest + marketplace …

• Serverless Architecture

  … Functions as a Service, event triggers, cold starts, pay-per-use pricing, managed backends, and the patterns and …

• Authentication, Authorization & API Security

  … Traditional web apps APIs, mobile apps, microservices Common pattern: a short-lived access token (15 min) plus a …

• Finding Service Boundaries with DDD

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

• Frontend Security

  … session=abc123; HttpOnly; Secure; SameSite=Lax; Path=/; Max-Age=86400 💡 A popular pattern is the BFF (Backend for …

• Database Indexing & Transactions

  … for that, see Sagas & the Outbox Pattern in the Microservices lessons. Key takeaways - Indexes turn O(n) scans …

• Normalization & Denormalization

  … I use BCNF for exceptional dependency patterns where a non-key determinant still creates redundancy. I denormalize only …

• Choosing an Architecture

  … else" Old["🏚️ Legacy system"] The strangler fig pattern: new features and migrated routes go to the new …