Skip to content

Spring Cloud - Eureka Server

Spring Cloud Eureka Server

程式碼：

  1. Eureka Server：https://github.com/aweit-zhu/SpringCloudEurekaServer
  2. Eureka Client：https://github.com/aweit-zhu/SpringCloudEurekaClient

Eureka Server

Alt text

  1. Service Registration: Microservices that want to be discovered by other services register themselves with the Eureka Server. Each microservice instance is identified by a unique application name and instance ID.
  2. Service Discovery: Services that need to communicate with other services can query the Eureka Server to obtain the network location (host and port) of the desired service instance. Eureka Server maintains a registry of available service instances and provides this information to the clients.
  3. Heartbeat Monitoring: Eureka Server continuously checks the health of registered service instances by sending periodic heartbeat requests. If a service instance fails to respond to the heartbeat requests within a certain time period, it is considered offline and removed from the registry.
  4. Load Balancing: Eureka Server can also act as a load balancer by providing a list of available service instances for a particular service. Clients can use this information to implement load balancing strategies, such as round-robin or random selection, when making requests to the service.
  5. High Availability: Multiple instances of the Eureka Server can be deployed in a cluster to ensure high availability and fault tolerance. Each Eureka Server instance in the cluster keeps its own local registry, and they replicate and synchronize the registration information among themselves.
  6. Integration with Spring Cloud: Spring Cloud provides integration with Eureka Server through the spring-cloud-starter-netflix-eureka-server dependency. It simplifies the setup and configuration of Eureka Server in a Spring Boot application.

Eureka Server - Code

  1. pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.14</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>eureka-server</artifactId>
    <version>1.0.0</version>
    <name>SpringCloudEurekaServer</name>
    <description>Eureka Server using Spring Boot</description>
    <properties>
        <java.version>11</java.version>
        <spring-cloud.version>2021.0.8</spring-cloud.version>
    </properties>
    <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-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>
  1. application.yaml
server:
  port: 8761

eureka:
  client:
    register-with-eureka: false
    fetch-registry: false
  1. Application.java：新增 @EnableEurekaServer
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@SpringBootApplication
@EnableEurekaServer
public class SpringCloudEurekaServerApplication {

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

}
  1. 啟動，並開啟瀏覽器，輸入：http://localhost:8761/

Alt text

Eureka Client - Code

  1. pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.14</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>eureka-client</artifactId>
    <version>1.0.0</version>
    <name>SpringCloudEurekaClient</name>
    <description>Eureka Client using Spring Boot</description>
    <properties>
        <java.version>11</java.version>
        <spring-cloud.version>2021.0.8</spring-cloud.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!-- Spring Cloud Config Client -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-config-client</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>
  1. application.properties
server.port=8888
spring.application.name=eureka-client-demo
eureka.client.service-url.defaultZone=http://localhost:8761/eureka
management.endpoints.web.exposure.include=*
  1. Application
@SpringBootApplication
@EnableDiscoveryClient
public class SpringCloudEurekaClientApplication {

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

}
  1. RestTemplateConfig.java
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

@Configuration
public class RestTemplateConfig {

    @Bean
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}
  1. EurekaClientDemoClient.java：eureka-client-demo 為服務註冊的名字。
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.ServiceInstance;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.stereotype.Component;

@Component
public class EurekaClientDemoClient {

    @Autowired
    private DiscoveryClient discoveryClient;

    public String getServiceUrl() {

        // Retrieve the instances of the service by application name
        List<ServiceInstance> instances = discoveryClient.getInstances("eureka-client-demo");

        // Choose one of the instances (e.g., the first one)
        ServiceInstance instance = instances.get(0);

        // Get the URL of the service instance
        String serviceUrl = instance.getUri().toString();

        return serviceUrl;
    }
}
  1. HelloController.java

@GetMapping("/hello")、@GetMapping("/hello-from-eureka") 皆為註冊到 Eureka 的方式，和原本的寫法一模一樣。

@GetMapping("/hello-from-eureka") 是為了要測試是否可以成功呼叫到Eureka 上的服務。serviceUrl就是 Eureka 的服務。

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.example.service.EurekaClientDemoClient;

@RestController
public class HelloController {

    @Autowired
    private RestTemplate restTemplate;

    @Autowired
    private EurekaClientDemoClient client;

    @GetMapping("/hello")
    public String hello() {
        return "Hello from Eureka Client!";
    }

    @GetMapping("/hello-from-eureka")
    public String hello2() {
        String serviceUrl = client.getServiceUrl();
        String helloUrl = serviceUrl + "/hello";
        String response = restTemplate.getForObject(helloUrl, String.class);
        return response;
    }
}

Test

http://localhost:8888/hello-from-eureka

Alt text