Java

Historical Netty 3 architecture and why its APIs/classes should not be projected onto modern Netty 4.x designs.

Centralized configuration, namespaces, change delivery, local caching, and operational considerations for Apollo-style config systems.

Eureka-style client registration and discovery, heartbeats, cached registries, and availability-oriented semantics.

Declarative HTTP interfaces, encoding/decoding, errors, timeouts, retries, and service-discovery integration.

Reactive API gateway routing, filters, cross-cutting policy, and the importance of non-blocking/backpressure-safe customization.

Historical Hystrix circuit breaker, timeout, fallback, and isolation concepts that remain useful even though the library is legacy.

Historical Ribbon client-side load balancing and durable instance-selection concepts.

Distributed trace/span propagation concepts and the transition from Spring Cloud Sleuth to newer observability stacks.

Netflix Zuul gateway/filter architecture and its place as historical context beside newer Spring gateway stacks.

Spring application-event publication, listener execution, transactions, asynchrony, and coupling considerations.