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Lessons (18)

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

  … pop → command.undo() You've used it: Ctrl+Z in every editor, Redux actions ( { type: "ADD TODO" } is …

• CQRS & Event Sourcing

  … Nobody tries to read the menu off the kitchen shelves. CQRS (Command Query Responsibility Segregation) separates: - Commands (writes …

• Which Pattern Do I Need?

  … Mediator coordinates many-to-many through a hub. Command vs Memento (undo) Command stores operations to reverse. Memento …

• Service Communication: Sync vs Async

  … and you need idempotency and ordering strategies. Commands vs events Command Event --- --- --- Meaning "Please do this" "This happened …

• What Are Design Patterns?

  … objects talk and share work? Chain of Responsibility, Command, Iterator, Mediator, Memento, Observer, State, Strategy, Template Method, Visitor …

• API Contracts, Gateways and Security

  … system-design-l6/api-security.svg) Define resource/command contracts, error shapes, pagination, idempotency and compatibility before implementation …

• Pods

  … busybox:1.36 command: ["sh", "-c", "until nc -z postgres 5432; do echo waiting for db; sleep 2 …

• Vertical Slice Architecture & the Modular Monolith

  … queries read directly, commands go through the domain. Rules of thumb Rule Why --- --- Maximise coupling inside a slice …

• Kubernetes Cluster Architecture

  … Every command ( kubectl , controllers, nodes) goes through its REST API. Validates and stores objects Head office reception etcd …

• Docker & Containers

  … Compose describes them all in YAML and starts them with one command. yaml compose.yaml services: api: build …

• MVC, MVP & MVVM

  … Model–View–ViewModel The ViewModel exposes observable state and commands . The View binds to them, so when the …

• Helm, kubectl Cheat Sheet & Best Practices

  … kubectl cheat sheet Task Command --- --- Apply YAML kubectl apply -f app.yaml / -f dir/ / -k overlay/ List things …

• Caching & Redis

  … Its data types solve many real problems: Type Commands Use case --- --- --- String SET , GET , INCR , EXPIRE Cache, counters …

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

  … transactions (rollback). 💡 Memento vs Command for undo: Memento stores snapshots (simple, memory-heavy). Command stores operations that know …

• Domain-Driven Design: Strategic Design

  … Then add commands, actors, policies and hot spots. Sticky note Colour Example --- --- --- Domain event 🟧 Orange Order Placed …

• ConfigMaps, Secrets & Storage

  … the Secret object can decode it in one command. Protect Secrets properly: Do Why --- --- Enable encryption at rest …

• Authentication, Authorization & API Security

  … rate limiting, short token lifetimes Injection (SQL, NoSQL, command) ' OR 1=1 -- returns every row Parameterised queries , never …

• Hexagonal Architecture (Ports & Adapters)

  … they call us)"] REST[REST controller] CLI[CLI command] Test[🧪 Test] Consumer[Kafka consumer] end subgraph Core …