一、服务治理

服务治理是分布式架构的基础设施服务，是微服务架构中核心模块，作用是微服务实例的自动化注册与发现。当微服务比较少的时候，通过静态配置就可以完成服务的调用。但当系统越来越复杂、相应的微服务应用也不断增加，静态配置就会难以维护。服务治理这时候主要实现以下功能：

• 服务注册
• 服务发现

Netflix的Eureka项目就是一个服务治理工具，开源地址：https://github.com/Netflix/eurekaEureka由两个组件组成：服务端和客户端。当一个中间层服务首次启动时，他会将自己注册到 Eureka 中，以便让客户端找到它，同时每 30 秒发送一次心跳。如果一个服务在几分钟内没有发送心跳，它将从所有 Eureka 节点上注销。

Spring Cloud Eureka，使用Netflix Eureka来实现服务注册与发现，支持通过Java实现分布式系统，或是与JVM兼容语言构建的系统。由于Eureka服务端的服务治理也提供了restful api，所以也支持非Java语言构建的微服务应用。

二、搭建服务注册中心

1. 新建一个maven项目

添加依赖：

<?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.xundh.test</groupId>
    <artifactId>eurekaserver1</artifactId>
    <version>1.0-SNAPSHOT</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/>
    </parent>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-eureka-server -->
        <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-actuator</artifactId>
        </dependency>

    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.RELEASE</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>

通过注解启用服务注册中心

package com.xundh.test;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;


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

bootstrap.yml

spring:
  application:
    name: eureka
  cloud:
    config:
      uri: ${CONFIG_SERVER_URL:http://localhost:8888}

设置application.yml：

server:
  port: 8761
  debug: true

eureka:
  client:
    registerWithEureka: false
    fetchRegistry: false
  server:
    waitTimeInMsWhenSyncEmpty: 0

配置说明：

• Server.port:服务端口
• eureka.client.register-with-eureka:该应用为注册中心，所以设置为false，不向注册中心注册自己
• eureka.client.fetch-registry: 注册中心的职责就是维护服务实例，它并不需要去检索服务，所以也设置为false

运行项目，访问网址 http://localhost:8761

2. 注册服务提供者

新建一个maven项目

设置 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>com.xundh.test</groupId>
    <artifactId>eurekaservice</artifactId>
    <version>1.0-SNAPSHOT</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/>
    </parent>
    <dependencies>
        <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>
        <!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-eureka -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
            <version>1.4.7.RELEASE</version>
        </dependency>

    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.RELEASE</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>

在启动类上加上@EnableDiscoveryClient注解：

package com.xundh;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

@SpringBootApplication
@EnableDiscoveryClient
public class ServiceApplication {
    public static void main(String[] args) {
        SpringApplication.run(ServiceApplication.class, args);
    }
}

建一个RestController

package com.xundh;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.discovery.DiscoveryClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;


@RestController
public class HelloController {
    private final Logger logger = LoggerFactory.getLogger(HelloController.class);
    @Autowired
    private DiscoveryClient client;

    @RequestMapping(value="/hello", method = RequestMethod.GET)
    public String index(){
//        ServiceInstance instance = client.
        logger.info("/hello,host");
        return "Hello World";
    }
}

配置文件application.yml

spring:
  application:
    name: my-eureka-service
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/

启动后，在注册中心可以看到注册了新的服务。