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Eureka server and Client Communicate

Eureka server and Client Communicate

Eureka Server is a service registry provided by Netflix as part of the Spring Cloud ecosystem. It acts as a discovery server where microservices can register themselves and discover other registered services.

Eureka server and Client Communicate

Eureka Client

Eureka Client is a microservice that registers itself with the Eureka Server. It also retrieves a list of other registered services from the Eureka Server, enabling it to discover and communicate with them.

Communication Process

  • 1. Service Registration: When a Eureka client starts, it registers itself with the Eureka server. This involves sending metadata about the service, such as its hostname, port, health indicator URL, and service ID.
  • 2. Service Discovery: When a client needs to communicate with another service, it queries the Eureka server to get the location (hostname and port) of the service it wants to communicate with.
  • 3. Heartbeat: The client sends periodic heartbeats to the Eureka server to renew its lease and let the server know it’s still active.
  • 4. Service De-registration: When a client shuts down, it sends a de-registration request to the Eureka server to remove itself from the registry.

Java Example

Here’s a basic Java example using Spring Boot to demonstrate how Eureka Server and Client communicate.

Step 1: Set up Eureka Server
```xml
<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>
```

application.properties
```properties
server.port=8761
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false
```

EurekaServerApplication.java
```java
@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaServerApplication.class, args);
    }
}
```

Step 2: Set up Eureka Client
```xml
<dependencies>
    <dependency>
        <groupId>org.springframework.cloud</groupId>
        <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
</dependencies>
```

application.properties
```properties
server.port=8080
eureka.client.service-url.defaultZone=http://localhost:8761/eureka/
spring.application.name=eureka-client
```

EurekaClientApplication.java
```java
@SpringBootApplication
@EnableEurekaClient
public class EurekaClientApplication {
    public static void main(String[] args) {
        SpringApplication.run(EurekaClientApplication.class, args);
    }
}
```

Step 3: Service Discovery
```java
@RestController
public class ServiceController {

    @Autowired
    private DiscoveryClient discoveryClient;

    @GetMapping("/services")
    public List<String> getServices() {
        return discoveryClient.getServices();
    }

    @GetMapping("/instances/{serviceId}")
    public List<ServiceInstance> getServiceInstances(@PathVariable String serviceId) {
        return discoveryClient.getInstances(serviceId);
    }
}
```

In this setup:

  • 1. The Eureka server is set up on port 8761.
  • 2. A Eureka client registers itself with the Eureka server.
  • 3. The client can discover other services registered with the Eureka server.

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