Service Registry & Service Discovery (Eureka)

In a microservices architecture, services must communicate with each other. However, services are dynamic by nature, which makes direct communication difficult.

Service Registry and Service Discovery solve this problem.

What Problem Does Service Discovery Solve?

In a microservices environment:

Services scale up and down dynamically
Containers restart frequently
IP addresses and ports change
Hard-coding service URLs is impossible

Without service discovery:

Services become tightly coupled
Deployments break communication
Scaling becomes risky

Core Idea

Service Registry keeps track of all running services and their locations.
Service Discovery allows services to find each other dynamically at runtime.

What Is Eureka?

Eureka is Netflix’s open-source service registry and discovery solution, widely used with Spring Cloud.

Eureka follows a client-side service discovery model.

Components of Eureka

Eureka consists of two main components:

1️⃣ Eureka Server (Service Registry)

Central registry for all services
Stores service metadata:
- Service name
- IP address
- Port
- Status (UP / DOWN)
Exposes a discovery endpoint
Provides a dashboard

2️⃣ Eureka Client (Microservices)

Any microservice that:
- Registers itself with Eureka
- Discovers other services from Eureka
Sends periodic heartbeats to Eureka

How Eureka Works (Step-by-Step Flow)

Service starts
Service registers with Eureka Server
Eureka marks service as UP
Service sends heartbeat every 30 seconds
Client requests service details from Eureka
Load balancer selects an instance(if we have many)
Request is sent to the chosen instance

Setting Up Eureka Server (Spring Boot)

Step 1️⃣ Add Dependency

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

Step 2️⃣ Enable Eureka Server

@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {

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

Step 3️⃣ application.yml

server:
  port: 8761

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false

Access dashboard at: http://localhost:8761

Registering a Service with Eureka (Client)

Step 1️⃣ Add Dependency

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

Step 2️⃣ Enable Client

@EnableEurekaClient

In newer Spring Cloud versions, this is auto-enabled.

Step 3️⃣ application.yml

spring:
  application:
    name: ACCOUNT-SERVICE

server:
  port: 8085

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

Eureka Features We Should Know

Self-Healing

Services are not removed immediately
Prevents accidental removal due to temporary network issues

Client-Side Discovery

Client decides which instance to call
More scalable than server-side discovery

Status Updates

Services can publish:

UP
DOWN
OUT_OF_SERVICE
MAINTENANCE

Dashboard

Visual view of registered services
Health and metadata visibility

Why Use Eureka in Spring Cloud?

Easy to set up
Cloud-native design
Integrates well with:
- API Gateway
- LoadBalancer
- Resilience patterns
Avoids hard-coded service URLs

Eureka is a service registry used in microservices to dynamically discover service instances. Services register themselves with Eureka, send heartbeats, and clients use Eureka along with a load balancer to locate and communicate with other services.