What is Service Discovery and how does Eureka work in Spring Cloud? सर्विस डिस्कवरी क्या है और स्प्रिंग क्लाउड में Eureka कैसे काम करता है?

In a microservices system, service instances scale up/down and their network locations change dynamically, so hardcoding IP addresses and ports doesn't work. Service Discovery solves this: each service registers itself with a central registry on startup, and other services query the registry to find available instances at runtime instead of using a fixed address.

Netflix Eureka, integrated via Spring Cloud Netflix, provides this registry. A Eureka Server is run as its own Spring Boot app with @EnableEurekaServer; each microservice becomes a Eureka Client with @EnableEurekaClient (or auto-detected via the client dependency), sending periodic heartbeats to stay registered, and load-balanced calls between services are resolved by service name rather than a hardcoded host.

@SpringBootApplication
@EnableEurekaServer
public class DiscoveryServerApplication { ... }

eureka:
  client:
    service-url:
      defaultZone: http://localhost:8761/eureka/