服务注册与发现Eureka(Finchley版本)

服务注册与发现Eureka(Finchley版本)

创建服务注册中心,采用Eureka作为服务注册与发现的组件。

创建maven主工程

首先创建一个主Maven工程,在其pom文件引入依赖,spring Boot版本为2.1.6.RELEASE,Spring Cloud版本为Finchley.RELEASE。这个pom文件作为父pom文件,起到依赖版本控制的作用,其他module工程继承该pom。

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>4.0.0modelVersion>

    <groupId>com.siregroupId>
    <artifactId>springcloude_test04artifactId>
    <version>1.0-SNAPSHOTversion>

    <parent>
        <groupId>org.springframework.bootgroupId>
        <artifactId>spring-boot-starter-parentartifactId>
        <version>2.1.6.RELEASEversion>
        <relativePath/>
    parent>

    <modules>
        <module>eureka_servermodule>
        <module>eureka_clientmodule>
    modules>

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

    <dependencies>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-testartifactId>
            <scope>testscope>
        dependency>
    dependencies>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloudgroupId>
                <artifactId>spring-cloud-dependenciesartifactId>
                <version>${spring-cloud.version}version>
                <type>pomtype>
                <scope>importscope>
            dependency>
        dependencies>
    dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
            plugin>
        plugins>
    build>
project>

服务注册中心Eureka server

创建一个module,右键工程->创建model-> 选择spring initialir 如下图:

下一步->选择cloud discovery->eureka server ,然后一直下一步就行了。

pom

其pom.xml继承了父pom文件,引入spring-cloud-starter-netflix-eureka-server的依赖。

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>4.0.0modelVersion>
   
    <
parent>
        <groupId>com.siregroupId>
        <artifactId>springcloude_test04artifactId>
        <version>1.0-SNAPSHOTversion>
        <relativePath/>
   
parent>
   
    <
groupId>com.siregroupId>
    <artifactId>eureka_serverartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>eureka_servername>
    <description>Demo project for Spring Bootdescription>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-serverartifactId>
        dependency>
    dependencies>

project>

注解@EnableEurekaServer

注解@EnableEurekaServer需在springboot工程的启动application类上加:

appication.yml

eureka是一个高可用的组件,无后端缓存,每一个实例注册之后需向注册中心发送心跳(可在内存中完成),默认情况erureka server也是一个eureka client ,必须要指定一个 server。eureka server的配置文件appication.yml:

#端口
server:
 
port: 8761
# eureka配置
eureka:
 
instance:
   
hostname: localhost
 
# 通过eureka.client.registerWithEureka:false和fetchRegistry:false来表明自己是一个eureka server.
 
client:
   
registerWithEureka: false
    fetchRegistry
: false
    serviceUrl
:
    
defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

spring:
 
application:
   
name: eurka_server

启动

访问http://localhost:8761/

服务提供中心Eureka client

当client向server注册时,会提供一些元数据,如主机和端口,URL,主页等。Eureka server 从每个client实例接收心跳消息。如心跳超时,则通常将该实例从注册server中删除。创建过程同server类似。

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>4.0.0modelVersion>
   
    <
parent>
        <groupId>com.siregroupId>
        <artifactId>springcloude_test04artifactId>
        <version>1.0-SNAPSHOTversion>
        <relativePath/>
   
parent>
   
    <
groupId>com.siregroupId>
    <artifactId>eureka_clientartifactId>
    <version>0.0.1-SNAPSHOTversion>
    <name>eureka_clientname>
    <description>Demo project for Spring Bootdescription>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloudgroupId>
            <artifactId>spring-cloud-starter-netflix-eureka-clientartifactId>
        dependency>
        <dependency>
            <groupId>org.springframework.bootgroupId>
            <artifactId>spring-boot-starter-webartifactId>
        dependency>
    dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.bootgroupId>
                <artifactId>spring-boot-maven-pluginartifactId>
            plugin>
        plugins>
    build>

project>

注解@EnableEurekaClient

通过注解@EnableEurekaClient 表明自己是一个eureka client

@SpringBootApplication
@EnableEurekaClient
@RestController

public class EurekaClientApplication {

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

   
@Value("${server.port}")
    String
port;
   
   
@RequestMapping("/hello")
   
public String hello(@RequestParam(value = "name", defaultValue = "sire") String name){
       
return "hi " + name + " ,i am from port:" + port;
    }
}

application.yml

spring.application.name这个很重要,以后的服务间相互调用一般都是根据这个name。

配置文件中注明服务注册中心的地址,application.yml配置文件如下:

server:
 
port: 8762

spring:
 
application:
   
name: service_client

eureka:
 
client:
   
serviceUrl:
     
defaultZone: http://localhost:8761/eureka/

启动

运行EurekaClientApplication(需先将EurekaServerApplication

启动),然后打开http://localhost:8761/

访问http://localhost:8762/hello出现内容

注意

当将客户端关闭后,再次打开Eureka的注册页面,发现有一串红字:

EMERGENCY! EUREKA MAY BE INCORRECTLY CLAIMING INSTANCES ARE UP WHEN THEY'RE NOT. RENEWALS ARE LESSER THAN THRESHOLD AND HENCE THE INSTANCES ARE NOT BEING EXPIRED JUST TO BE SAFE.

这是因为Eureka进入了自我保护机制,默认情况下,如果EurekaServer在一定时间内没有接收到某个微服务实例的心跳时,EurekaServer将会注销该实例(默认90s)。但是当网络发生故障时,微服务与EurekaServer之间无法通信,这样就会很危险了,因为微服务本身是很健康的,此时就不应该注销这个微服务,而Eureka通过自我保护机制来预防这种情况,当网络健康后,该EurekaServer节点就会自动退出自我保护模式;

这时再次将服务端启动后再重启客服端,刷新服务注册中心会发现,自我保护状态已取消。

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