Spring Cloud系列（一）服务的注册与发现Eureka（Finchley版本）

原文首发于：https://www.fangzhipeng.com/springcloud/2018/08/30/sc-f1-eureka/
本文出自方志朋的博客

一、创建服务注册中心

1、创建一个maven主工程

首先创建一个maven主工程，在pom文件中引入依赖，Spring Boot版本为2.0.5.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，其它module工程继承这个pom。本系列所有文章都用这个pom。

代码如下：

<?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>com.hxk.springcloud</groupId>
    <artifactId>SCMain</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>SCMain</name>
    <description>Demo project for Spring Boot</description>

    <!--不知道parent的版本就在这里找C:\Users\hxk\.m2\repository\org\springframework\boot\spring-boot-parent\
   这个路径下有常用的依赖 C:\Users\hxk\.m2\repository\org\springframework\boot\spring-boot\1.4.0.RELEASE 下面有个pom文件-->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.5.RELEASE</version>
        <relativePath/>
    </parent>

    <modules>
        <module>eureka-server</module>
        <module>eureka-client</module>
    </modules>

    <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.RELEASE</spring-cloud.version>
    </properties>

    <dependencies>
        <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、创建服务注册中心

一个model工程作为服务注册中心，即Eureka Server,另一个作为Eureka Client。下面以服务为例记录下步骤：

右键->new->module->Spring Initializr

next->Cloud Discovery->选择Eureka Server

一直next到底

创建完的工程，其pom继承了父类的pom，并引入了spring-cloud-starter-netflix-eureka-server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>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>eureka-server</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>eureka-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>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.25</version>
        </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、启动一个服务注册中心

只需要一个注解@EnableEurekaServer，这个注解需要在springboot工程的启动application类上加

@SpringBootApplication
@EnableEurekaServer
public class EurekaServerApplication {

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

4、eureka是一个高可用的组件，它没有后端缓存，每一个实例注册之后需要向注册中心发送心跳（因此可以在内存中完成），在默认情况下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：

server:
  port: 8081

eureka:
  instance:
    hostname: localhost
  client:
    registerWithEureka: false
    fetchRegistry: false
    serviceUrl:
      defaultZone: http://${eureka.instance.hostname}:${server.port}/eureka/

spring:
  application:
    name: eurka-server

通过eureka.client.registerWithEureka：false和fetchRegistry：false来表明自己是一个eureka server。

5、启动server，访问 http://localhost:8081/

此时还没有注册服务

3、创建服务提供者

当client向server注册时，它会提供一些元数据，例如主机和端口，URL，主页等。

Eureka server 从每个client实例接收心跳消息。如果心跳超时，则通常将该实例从注册server中删除。

创建过程同server类似,创建完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>com.hxk</groupId>
    <artifactId>eureka-client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>eureka-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.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.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.25</version>
        </dependency>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>RELEASE</version>
            <scope>compile</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>

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);
    }

    @RequestMapping("/index")
    public String index(){
        return "Hello World";
    }
}

application.yml配置文件如下：

server:
  port: 8082

spring:
  application:
    name: eureka-client

eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8081/eureka/

需要指明spring.application.name,这个很重要，这在以后的服务与服务之间相互调用一般都是根据这个name

启动client，访问 http://localhost:8082/index

再次访问http://localhost:8081/

发现服务已经成功注册在服务中心里

To be continued...

Spring Cloud系列（一）服务的注册与发现Eureka（Finchley版本）

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