WebFlux Reactive Patterns

Use WebFlux when the complete request path can benefit from non-blocking I/O.

Pipeline rules

• Return Mono or Flux; do not call subscribe() in request-handling code.
• Compose work with map, flatMap, concatMap, and zip according to ordering requirements.
• Keep blocking JDBC, filesystem, and legacy SDK calls out of event-loop threads.
• Isolate unavoidable blocking calls on boundedElastic at the narrow adapter boundary.
• Apply timeouts at remote-call boundaries and preserve cancellation.

Context and errors

• Put request-scoped metadata in Reactor Context, not ThreadLocal.
• Translate domain failures centrally without swallowing cancellation or infrastructure errors.
• Use onErrorResume only when a defined fallback exists.
• Avoid onErrorContinue; it makes partial processing hard to reason about.