Spring Cloud实战(二)-Spring Cloud Eureka

概要

什么是Spring Cloud Eureka?

使用Eureka获取服务调用

Eureka整合Spring Config Server

构建Eureka Server集群

什么是Spring Cloud Eureka?

Spring Cloud Eureka 模块提供的功能是被动式的服务发现.
什么是服务发现?
服务发现就像聊天室一个,每个用户来的时候去服务器上注册,这样他的好友们就能看到你,你同时也将获取好友的上线列表.
在微服务中,服务就相当于聊天室的用户,而服务注册中心就像聊天室服务器一样,目前服务发现的解决方案有Eureka,Consul,Etcd,Zookeeper,SmartStack,等等.

本文就来讲讲Eureka,如图所示,Eureka Client通过HTTP(或者TCP,UDP)去Eureka Server注册和获取服务列表,为了高可用一般会有多个Eureka Server组成集群.Eureka会移除那些心跳检查未到达的服务.

使用Eureka获取服务调用

这节我们将构建一个Eureka Server,5个Eureka Client(分别提供主语,动词,量词,形容词,名词服务),再构建一个Sentence Eureka Client 来用前面五个服务造句.

1.创建mmb-eureka-server

添加依赖-spring-cloud-starter-parent,spring-cloud-starter-eureka-server(pom.xml)

 <parent><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-parent</artifactId><version>Brixton.SR4</version><relativePath/></parent><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka-server</artifactId></dependency></dependencies>

配置应用信息-端口和应用名称 application.yml

server:port: 8010spring:application:name: mmb-eureka-server

启动服务

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

打开管理页面,检查是否成功

2.创建mmb-eureka-client

添加依赖-spring-cloud-starter-parent,spring-cloud-starter-eureka (pom.xml)

  <parent><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-parent</artifactId><version>Brixton.SR4</version><relativePath/></parent><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</artifactId></dependency></dependencies>

配置应用信息-eureka server信息,实际使用的words信息,端口号 (application.yml)

eureka:client:service-url:defaultZone: http://localhost:8010/eureka/words: 你,我,他server:port: ${PORT:${SERVER_PORT:0}}
#  这个的意思是随机指定个没使用的端口

配置启动信息-应用名称 (bootstrap.xml)

spring:application:name: mmb-eureka-client-subject

添加Controller-随机获取words中的一条

@RestController
public class Controller {@Value("${words}") String words;@RequestMapping("/")public  String getWord() {String[] wordArray = words.split(",");int i = (int)Math.round(Math.random() * (wordArray.length - 1));return wordArray[i];}
}

启动服务

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

访问127.0.0.1/port(看日志可以得到各个应用的port) 看到words里的词就启动成功了,

其它的verb,acticle,adjective,noun工程类似,就把words,和spring.application.name改成对应的工程名字就好了

3.创建sentence工程

添加依赖-spring-cloud-starter-parent,spring-cloud-starter-eureka,spring-boot-starter-web,spring-boot-starter-actuator (pom.xml)

  <parent><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-parent</artifactId><version>Brixton.SR4</version><relativePath/></parent><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-eureka</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-actuator</artifactId></dependency></dependencies>

配置应用信息-eureka server和端口号 (application.yml)

eureka:client:serviceUrl:defaultZone: http://localhost:8010/eureka/server:port: 8020

配置启动信息-应用名称 (bootstrap.yml)

spring:application:name: mmb-eureka-sentence

添加Controller-用其他eureka-clients(subject,verb,acticle,adjective,noun)的各个服务造句

@RestController
public class Controller {@AutowiredDiscoveryClient client;@RequestMapping("/sentence")public  String getSentence() {returngetWord("mmb-eureka-client-subject") + " "+ getWord("MMB-EUREKA-CLIENT-VERB") + " "+ getWord("mmb-eureka-client-article") + " "+ getWord("mmb-eureka-client-adjective") + " "+ getWord("mmb-eureka-client-noun") + ".";//大小写不区分}public String getWord(String service) {List<ServiceInstance> list = client.getInstances(service);if (list != null && list.size() > 0 ) {URI uri = list.get(0).getUri();if (uri !=null ) {return (new RestTemplate()).getForObject(uri,String.class);}}return null;}
}

启动服务

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

先启动Eureka Server,再启动Eureka Client,在管理页面上看到服务都起成功时,访问127.0.0.1/8020/sentence 可以得到一个随机组成的句子

Eureka整合Spring Config Server

在git的repository里添加application.yml

 eureka:client:serviceUrl:defaultZone: http://localhost:8010/eureka/

启动实战(一)中的Spring Cloud Config Server
修改各个client的配置
- application.yml移除属性eureka.client.serviceUrl.defaultZone
- bootstrap.yml添加属性 spring.cloud.config.uri: http://localhost:8001
- pom.xml添加依赖spring-cloud-config-client
依次启动Config Server,Eureka Server,Eureka Client,在管理页面上看到服务都起成功时,访问127.0.0.1/8020/sentence 可以得到一个随机组成的句子
-
如果你想把words信息也放入repository呢?在application.yml中添加,如下信息,各个client启动的时候加上-Dspring.profiles.active对应到相应的启动参数就行了.

    ---spring:profiles: subjectwords: I,You,He,She,It---spring:profiles: verbwords: ran,knew,had,saw,bought---spring:profiles: articlewords: a,the---spring:profiles: adjectivewords: reasonable,leaky,suspicious,ordinary,unlikely---spring:profiles: nounwords: boat,book,vote,seat,backpack,partition,groundhog

构建Eureka Server集群

host文件中添加 (c:WINDOWSsystem32driversetchosts).

  127.0.0.1       eureka-primary127.0.0.1       eureka-secondary127.0.0.1       eureka-tertiary

Eureka Server的application.yml添加多个profiles,和instanceId

 ---
spring:application:name: eureka-server-clustered   profiles: primary
server:port: 8011
eureka:instance:hostname: eureka-primary       ---
spring:application:name: eureka-server-clustered      profiles: secondary
server:port: 8012
eureka:instance:hostname: eureka-secondary       ---
spring:application:name: eureka-server-clustered      profiles: tertiary
server:port: 8013
eureka:instance:hostname: eureka-tertiary

此时Eureka Server 同时也是个Eureka Client,需要设置eureka.client.serviceUrl.defaultZone,值是另外两个,最终会是下面这样

---
spring:application:name: eureka-server-clustered   profiles: primary
server:port: 8011
eureka:instance:hostname: eureka-primary       client:registerWithEureka: truefetchRegistry: true        serviceUrl:defaultZone: http://eureka-secondary:8012/eureka/,http://eureka-tertiary:8013/eureka/---
spring:application:name: eureka-server-clustered      profiles: secondary
server:port: 8012
eureka:instance:hostname: eureka-secondary       client:registerWithEureka: truefetchRegistry: true        serviceUrl:defaultZone: http://eureka-tertiary:8013/eureka/,http://eureka-primary:8011/eureka/---
spring:application:name: eureka-server-clustered      profiles: tertiary
server:port: 8013
eureka:instance:hostname: eureka-tertiary       client:registerWithEureka: truefetchRegistry: true    serviceUrl:defaultZone: http://eureka-primary:8011/eureka/,http://eureka-secondary:8012/eureka/

以-Dspring.profiles.active=primary (and secondary, and tertiary)为启动参数分别启动Eureka Server
修改所有Eureka Client的eureka.client.serviceUrl.defaultZone值为http://eureka-primary:8011/eu...逗号分隔,无空白),集群启动成功登录管理页面查看,如下图所示即成功
再启动所有的Eureka Clients,查看http://localhost:8020/sentence 是否成功
为了测试容错性,关掉两个Eureka Client,重启若干个Eureka Client,观察启动是否报错,再去查看查看http://localhost:8020/sentence 是否成功