Service Discovery

🔍 What Is It?

Service discovery is the mechanism by which microservices locate each other.

Components:

• →Eureka Server — the service registry (a Spring Boot app with @EnableEurekaServer)
• →Eureka Client — each microservice registers itself (spring-cloud-starter-netflix-eureka-client)
• →Load Balancer — Spring Cloud LoadBalancer distributes calls across instances

Registration process:

1. Service starts, registers with Eureka (name, IP, port, health URL)
2. Sends heartbeats every 30 seconds to stay registered
3. If heartbeats stop, Eureka removes the instance after 90 seconds
4. Clients cache the registry locally — don't query Eureka on every call

🎯 Why Do We Need It?

In Kubernetes or cloud environments, service IP addresses change when pods restart. Hardcoding IPs is impossible. Service discovery provides stable logical names (order-service) that resolve to current instances dynamically. It also enables load balancing across multiple instances.

🏗️ What Happens in Real Projects?

In Kubernetes, you often use Kubernetes Service DNS instead of Eureka (Kubernetes has built-in service discovery). Eureka is more relevant in non-Kubernetes environments or when you need client-side load balancing with more control.

⚙️ How It Works

Services use lb://service-name URIs. Spring Cloud LoadBalancer intercepts these, queries the service registry for available instances, and selects one (round-robin by default). The actual HTTP call goes to the selected instance's IP and port.

💻 Example

Eureka Server and Client Setup — Setting up service registry and client registration.

// Eureka Server — standalone Spring Boot app
@SpringBootApplication
@EnableEurekaServer
public class ServiceRegistryApplication {
    public static void main(String[] args) {
        SpringApplication.run(ServiceRegistryApplication.class, args);
    }
}

// application.yml for Eureka Server
// server:
//   port: 8761
// eureka:
//   client:
//     register-with-eureka: false  # Don't register itself
//     fetch-registry: false
//   server:
//     wait-time-in-ms-when-sync-empty: 0

🤔 Common Confusions

🚨 Common Production Issues

✅ Best Practices

🏛️ Architect's Note

💬 Frequently Asked Questions

🎯 Key Takeaways

🔗 Related Topics

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