Reactive Microservices: Key characteristics of a reactive microservice include: 1. Responsiveness: Reactive microservices are designed to respond quickly to incoming requests. They achieve this by employing non-blocking I/O operations and asynchronous communication patterns. 2. Resilience: They are resilient to failures in the system or dependencie. This is achieved through techniques such as isolation, bulkheading and employing strategies like timeouts and retries. 3. Elasticity: Reactive microservices an scale components independently based on demand. They leverage features such as actor model, reactive streams or message brokers to handle varying workloads effectively. 4. Message-driven: Communication between microservices and external systems is often based on asyncronous messaging patterns. This approach helps in ecoupling services and ensuring loose coupling. 5. Event-driven: They often make use of event-driven architecturs where changes or events in the system trigger actions or updates across different microservices. 6. Functional programming: Reactive microservices may also use functional programming concepts to handle state changes and transformations in a predictable and scalable manner. In summary, a reactive microservice is designed to handle modern challenges such as scalability, responsiveness and resilience in distributed systems through the application of reactive programming principles. This approach is particularly beneficial in environments where real-time responsiveness and resilience to failure are critical requierements. References: Google's project Borg, Netflix OSS, Spring Boot, JHipster, Okta.