Spring Cloud入门笔记（一）构建Eureka/Ribb

1.Eureka/Ribbon基本概念

Eureka是Spring Cloud全家桶中，服务注册、发现的组件。
Eureka主要由三个模块构成

• 服务注册中心：
  （1）服务注册，新服务都需要在注册中心进行注册；
  （2）服务发现，服务需求方，即Eureka客户端来注册中心进行服务发现，获取需要的服务地址；
  （3）服务管理，维护各个服务的健康情况，保证服务的可用性

• 服务提生产者，提供各种服务

• 服务消费者（client），使用生产者提供的服务

  
  Eureka基本原理，图片来自网络

• Ribbon：主要功能为保障服务访问的负载均衡

---

2.构建Eureka 服务注册发现中心

2.1 创建一个spring boot工程
pom.xml如下：

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>xyz.onepig</groupId>
    <artifactId>discovery-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>discovery-server</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.SR1</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-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>
            </plugin>
        </plugins>
    </build>


</project>

2.2在入口文件中添加注解

@SpringBootApplication
@EnableEurekaServer
public class DiscoveryServerApplication {

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

2.3配置文件如下：
/resources/application.roperties

spring.application.name=discovery-server
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false
server.port=8761

2.4启动注册中心
（启动server的spring boot），访问本地8761端口，出现如下界面，则server创建成功。

server

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3.构建Eureka server 服务生产者

3.1创建一个spring boot工程
pom.xml如下：

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>xyz.onepig</groupId>
    <artifactId>time-service</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>time-service</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.SR1</spring-cloud.version>
    </properties>

    <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>

        <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>
            </plugin>
        </plugins>
    </build>
</project>

3.2编写服务生产者代码
我们在这里构建一个时间查询服务，用于返回当前时间，代码如下，关键注解为@EnableDiscoveryClient，功能是注册服务。

@SpringBootApplication
@EnableDiscoveryClient
@RestController
public class TimeServiceApplication {

    @Value("${server.port}")
    private int port;
    
    public static void main(String[] args) {
        SpringApplication.run(TimeServiceApplication.class, args);
    }
    
    @GetMapping
    public String getTime() {
        return "The current time is " + new Date().toString() + "(answered by service running on " + port + ")";
    }
}

3.3配置文件如下：

/resources/application.roperties，注意service-url为服务发现server的地址

spring.application.name=time-service
eureka.client.service-url.defaultZone=http://localhost:8761/eureka
#eureka.instance.prefer-ip-address=true
eureka.instance.instance-id=${spring.cloud.client.ip-address}:${spring.application.name}:${server.port}

3.4定制化启动
配置server.port参数为4444和5555（Edit Configurations），分别启动两个服务实例

配置server.port

可以看到Eureka控制中心已经出现了该服务的两个实例（Instances currently registered with Eureka），即刚才启动的4444和5555

服务已注册

---

4.构建Eureka客户端，使用Ribbon负载均衡

4.1创建一个spring boot工程
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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>xyz.onepig</groupId>
    <artifactId>time-client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>time-client</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
        <spring-cloud.version>Finchley.SR1</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-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>
            </plugin>
        </plugins>
    </build>

</project>

4.2主程序代码
其中关键注解为
@EnableDiscoveryClient：发现服务
@LoadBalanced：启用Ribbon

@SpringBootApplication
@RestController
@EnableDiscoveryClient
public class TimeClientApplication {

    @Autowired
    private RestTemplate restTemplate;
    
    public static void main(String[] args) {
        SpringApplication.run(TimeClientApplication.class, args);
    }
    
    @GetMapping
    public String getTime() {
        return restTemplate.getForEntity("http://time-service", String.class).getBody();
    }
    
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }
}

4.3配置文件
/resources/application.properties

spring.application.name=time-client
eureka.client.service-url.defaultZone=http://localhost:8761/eureka
eureka.client.register-with-eureka=false
server.port=8081

4.4启动client
访问本机8081端口，刷新几次，可以看到访问被负载到了两个服务上：

4444
5555

本文参考：《极客时间-微服务建构实战160讲》

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