SpringCloud之服务注册与发现Eureka

一、SpringCloud Eureka介绍

Eureka是SpringCloud中的一个负责服务注册与发现的组件，是由 Netfix开发的服务发现框架，本身是一个基于REST的服务，遵循CAP理论的AP原则，

一个Eureka可分为Eureka Server和Eureka Client,Eureka Server提供服务注册服务，各个几点启动后，会在Eureka Server中注册，这样Eureka Server中的服务注册列表中将会存储所有可用服务节点的信息，服务节点的信息可以在界面中清晰的看到。

Eureka采用C-S架构，EurekaClient是一个java客户端，用于简化EurekaServer的交互，客户端同时也具备一个内置的，使用轮询负载算法的负载均衡器，在应用启动后，会向EurekaServer发送心跳（默认周期为30秒），如果EurekaServer在多个心跳周期内没有收到心跳，EurekaServer会将这个服务移除出去。

服务生产者将信息注册到Eureka,从而能使消费者能够找到，服务消费者从Eureka获取注册列表，从而能找到消费服务，这里服务生产者与服务消费者都为ureka Client

二、Eureka Server

这里实现单个的Eureka Server，新建一个SpringBoot项目

pom.xml导入EurekaServer的依赖

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

<?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>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>sprincloud-eureka</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>sprincloud-eureka</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>2020.0.3</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>

application.yml

server:
  port: 8761

spring:
  application:
    name: springcloud-eureka

eureka:
  instance:
    hostname: localhost
  client:
    register-with-eureka: false   #false标识不向注册中心注册子级
    fetch-registry: false
    service-url:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

启动类添加注解@EnableEurekaServer

启动项目，访问localhost:8761即可看到服务列表页面

 第一次启动这个地方Application应该没有任何服务

三、Eureka Client

1.添加依赖

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

<?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>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>springcloud-ekreka-client01</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>springcloud-ekreka-client01</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
        <spring-cloud.version>2020.0.3</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-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</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>
            </plugin>
        </plugins>
    </build>

</project>

2.application.yml，配置刚才注册中心的地址

server:
  port: 8090

spring:
  application:
    name: eureka-client-01

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

3.启动类添加注解@EnableEurekaClient

启动项目可以在服务列表中看到我们刚才新添加的服务