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

Spring Batch handles large-scale batch processing—ETL, data migration, report generation. Jobs contain steps; steps have readers, processors, and writers. Chunk-oriented processing reads, processes, and writes data in configurable batches. ItemReader

GraphQL provides flexible APIs where clients specify exact data requirements. Spring for GraphQL integrates GraphQL Java with Spring Boot. Schema-first approach defines types in .graphqls files. Resolvers map schema fields to Java methods using @Query

Feature flags (feature toggles) enable/disable functionality without code deployment. I use libraries like Togglz or FF4J for flag management. Flags support A/B testing, canary releases, and emergency kill switches. Strategy pattern determines flag st