Spring Boot - Eureka Server

Eureka Server acts as a service registry that holds information about all available microservice instances. It enables automatic registration of services and simplifies inter-service communication without hardcoding IP addresses or hostnames.

Functions:

• Client Registration: Microservice instances register themselves with the Eureka Server upon startup.
• Service Discovery: Other microservices can look up registered instances using the registry for communication.

Why use Eureka Server in Spring Boot Applications?

Eureka Server follows the Register–Lookup–Connect principle. This approach simplifies service management in distributed environments.

• Centralized Service Registry: Maintains a directory of all available microservices and their network locations.
• Automatic Registration: Clients automatically register and deregister with Eureka Server, reducing manual configurations.
• Load Balancing Support: Enables client-side load balancing using libraries such as Ribbon.
• Health Monitoring: Supports health checks to ensure only healthy instances remain discoverable.
• Seamless Spring Cloud Integration: Works efficiently within the Spring Cloud ecosystem, making scaling and deployment simpler.

Configuring the Eureka Server

Step 1. Maven Dependencies

Add the following dependencies in the pom.xml file of both server and client applications.

<!-- Eureka Client -->
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
</dependency>

<!-- Eureka Server -->
<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
</dependency>

Ensure that Spring Cloud dependencies are imported using dependencyManagement.

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.cloud</groupId>
      <artifactId>spring-cloud-dependencies</artifactId>
      <version>2021.0.5</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

Step 2. Enabling Eureka Functionality

Use annotations to activate Eureka functionality.

• @EnableEurekaServer: Marks a Spring Boot application as the Eureka Server.
• @EnableEurekaClient: Enables Eureka registration and discovery for client services.

No additional bean configuration is required for basic setups.

Step 3. Application Properties

Define Eureka-related configurations in application.yml or application.properties.

eureka:
instance:
prefer-ip-address: true
client:
fetch-registry: true
register-with-eureka: true
service-url:
defaultZone: http://localhost:8761/eureka
spring:
application:
name: TEACHER-APP

The prefer-ip-address: true property ensures that clients register using their IP address instead of hostname.

Implementing Eureka Configuration

For marking a Spring Boot Application as an Eureka Server.

Step 1. Eureka Server Application

package org.geeksforgeeks.registry.serviceregistry;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@SpringBootApplication
@EnableEurekaServer
public class ServiceRegistryApplication {

    public static void main(String[] args) {
        SpringApplication.run(ServiceRegistryApplication.class, args);
    }
}

Step 2. Eureka Client Application

package org.geeksforgeeks.student;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.EnableEurekaClient;

@SpringBootApplication
@EnableEurekaClient
public class StudentApplication {

    public static void main(String[] args) {
        SpringApplication.run(StudentApplication.class, args);
    }
}

Step 3. Eureka Dashboard

Once the Eureka Server is running, access the dashboard at:

URL: http://localhost:8761

The dashboard displays all registered microservices and their statuses. Example registered services:

• API-GATEWAY
• STUDENT-APP
• TEACHER-APP

Use Cases of Eureka Server

Eureka Server is widely used in:

• Microservices Architecture: Core component for service registration and discovery.
• Distributed Systems: Simplifies service communication and dependency management.
• Load Balancing and Failover: Works with load balancers for efficient traffic distribution.

Alternatives to Eureka Client

While Eureka is widely adopted, other tools also offer service registration and discovery features:

• Consul: Developed by HashiCorp, supports health checking, key-value storage, and multi-datacenter setups.
• Apache ZooKeeper: Provides service discovery and configuration management, often used in large distributed systems.
• Etcd: Lightweight and ideal for Kubernetes-based environments requiring high availability.