What are the principles of the Reactive Manifesto and how do they apply to microservices?

The Reactive Manifesto describes four principles for building responsive, resilient distributed systems. Responsive: the system responds in a timely manner under all conditions, establishing reliable upper bounds on response time. Resilient: the system stays responsive in the face of failure, achieved through replication, containment, isolation, and delegation — failures are isolated so they don't cascade. Elastic: the system scales automatically under varying workloads by adding or removing resources. Message-driven: components communicate via asynchronous message passing with explicit message boundaries, enabling loose coupling and backpressure. In microservices, these principles translate to: designing stateless, independently scalable services; using circuit breakers and bulkheads for resilience; employing async event-driven communication; and implementing backpressure in stream processing (Reactive Streams, Project Reactor, RxJava).