Eureka is a service discovery tool provided by Spring Cloud that helps manage microservices and their communication within a distributed system. It acts as a registry where services can register themselves and discover other services.

Purpose of Eureka in a Spring Cloud application

  1. Service Registration and Discovery:
    • Services in a microservices architecture can register themselves with Eureka Server upon startup. Once registered, they are discoverable by other services.
    • Clients (other services) can query Eureka to find the addresses of services they need to communicate with.
  2. Load Balancing:
    • Eureka supports client-side load balancing. When a service needs to call another, it queries Eureka for available instances and distributes requests across them to ensure efficient load balancing.
  3. Fault Tolerance:
    • Eureka supports automatic service health checks. If a service instance fails or is unavailable, Eureka removes it from the registry, ensuring that calls are not directed to unhealthy instances.
  4. Decouples Services:
    • By using Eureka, services do not need to know the exact location (IP address or hostname) of each other. Instead, they rely on the Eureka server for discovery, reducing tight coupling.
  5. Dynamic Scalability:
    • Eureka supports dynamic scaling. As new instances of services are added or removed, Eureka keeps the registry updated, ensuring that service instances are available for discovery.

Example

  1. Eureka Server Setup:
    • In a Spring Boot application, you can set up Eureka Server by adding the spring-cloud-starter-netflix-eureka-server dependency and annotating the main class with @EnableEurekaServer.
    @SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }
}
  2. Eureka Client:
    • A microservice can register with Eureka by adding spring-cloud-starter-netflix-eureka-client and using the @EnableEurekaClient annotation.
    @SpringBootApplication
@EnableEurekaClient
public class MyServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyServiceApplication.class, args);
    }
}

In summary, Eureka in a Spring Cloud application facilitates service discovery, load balancing, and fault tolerance, enabling efficient communication and management of microservices within a distributed system.