Ruby's closures—blocks, procs, lambdas—enable functional programming patterns. Blocks are anonymous code chunks passed to methods. Procs are objects wrapping blocks, callable with call. Lambdas are stricter procs—check argument count and return differ

Sidekiq processes background jobs asynchronously using Redis and multi-threading. ActiveJob provides framework-agnostic interface—I use it for portability between job processors. Jobs handle emails, data processing, API calls, report generation. perfo

RSpec provides powerful testing tools for behavior-driven development. Shared examples reduce duplication across similar specs—I extract common behavior into reusable examples. Contexts organize tests by different scenarios. Let blocks lazily evaluate

Service objects extract complex business logic from models and controllers, following Single Responsibility Principle. I structure services with a clear public interface—typically a call method. Services handle multi-step operations, external API call

Ruby's metaprogramming enables dynamic method definition and interception. method_missing catches undefined method calls, allowing DSL creation and proxy patterns. I implement it carefully with respond_to_missing? for proper introspection. define_meth

Kubernetes orchestrates containerized applications at scale. Deployments manage ReplicaSets ensuring desired pod count. Services expose pods with stable endpoints. ConfigMaps externalize configuration. Secrets store sensitive data. Resource limits pre

Resilience4j provides resilience patterns for fault tolerance. Circuit breakers prevent cascading failures—open after threshold failures, allow retry after timeout. Rate limiters control request rates. Retry mechanisms handle transient failures. Bulkh

AOP separates cross-cutting concerns from business logic. Aspects modularize logging, security, transactions, caching. @Aspect defines aspect classes. @Before, @After, @Around specify advice timing. Pointcuts select join points using expressions. @Aro

Multi-tenancy serves multiple customers (tenants) from single application instance. Schema-per-tenant isolates data in separate databases. Shared schema with tenant ID column partitions data within tables. Discriminator-based approach uses JPA filters

Spring's event mechanism enables loose coupling between components. ApplicationEventPublisher publishes events. @EventListener handles events asynchronously or synchronously. Events extend ApplicationEvent or are POJOs. @TransactionalEventListener pub

Elasticsearch provides powerful full-text search capabilities. Spring Data Elasticsearch offers repository abstraction similar to JPA. @Document annotates entity classes with index mapping. @Field customizes field types and analyzers. Queries use meth

WebSocket enables full-duplex communication between client and server. Spring WebSocket supports STOMP protocol over WebSocket. I configure message brokers for pub-sub messaging. @MessageMapping handles incoming messages. SimpMessagingTemplate sends m