SpringCloud学习笔记：服务注册与发现Eureka（2）
1. Eureka简介
Eureka是一个用于服务注册和发现的组件，分为Eureka Server和Eureka Client，Eureka Server为Eureka服务注册中心，Eureka Client为Eureka客户端。
Eureka是SpringCloud首选推荐的注册与服务发现组件，与SpringCloud其他组件可以无缝对接。
Eureka的基本框架主要包括3种角色：
◊ Register Service：服务注册中心，是一个Eureka Server，提供服务注册与发现功能；
◊ Provider Service：服务提供者，是一个Eureka Client，提供服务；
◊ Consumer Service：服务消费者，是一个Eureka Client，消费服务。
服务消费基本过程：
（1）首先需要一个服务注册中心Eureka Server；
（2）服务提供者Eureka Client向服务注册中心Eureka Server注册，将自己的信息（服务名、服务IP地址）通过REST API的形式提交注册周年更新Eureka Server；
（3）服务消费者Eureka Client向服务注册中心Eureka Server注册，服务消费者获取服务注册列表信息。该列表信息包含所有向服务注册中心Eureka Server注册的服务信息；
（4）服务消费者Eureka Client获取服务注册列表信息之后，获得服务提供者的IP地址，通过HTTP远程调度来消费服务提供者的服务。
2. Eureka示例项目
项目结构：采用Maven多Module结构
主Maven项目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>libing</groupId> <artifactId>libing-eureka</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>pom</packaging> <name>libing-eureka</name> <description>Demo project for Spring Boot</description> <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.1.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.M9</spring-cloud.version> </properties> <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-dependencies</artifactId> <version>${spring-cloud.version}</version> <type>pom</type> <scope>import</scope> </dependency> </dependencies> </dependencyManagement> <modules> <module>eureka-server</module> <module>eureka-client</module> </modules> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-devtools</artifactId> <optional>true</optional> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <fork>true</fork> </configuration> </plugin> </plugins> </build> <repositories> <repository> <id>spring-milestones</id> <name>Spring Milestones</name> <url>https://repo.spring.io/milestone</url> <snapshots> <enabled>false</enabled> </snapshots> </repository> </repositories> </project>
2.1 Eureka Server
Eureka Server依赖项spring-cloud-starter-netflix-eureka-server
<?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>priv.libing</groupId> <artifactId>eureka-server</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>jar</packaging> <name>eureka-server</name> <description>Demo project for Spring Boot</description> <parent> <groupId>libing</groupId> <artifactId>libing-eureka</artifactId> <version>0.0.1-SNAPSHOT</version> </parent> <dependencies> <dependency> <groupId>org.springframework.cloud</groupId> <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId> </dependency> </dependencies> </project>
application.yml：
server:
port: 8761
eureka:
instance:
hostname: localhost
client:
fetch-registry: false # 禁用向自己注册
register-with-eureka: false # 只维护实例，不去检索服务
service-url:
default-zone: http://${eureka.instance.hostname}:${server.port}/eureka/
注：默认Eureka Server会向自己注册
EurekaServerApplication.java：
package priv.libing.eurekaserver; 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); } }
其中：注解@EnableEurekaServer开启Eureka Server功能。
启动程序，在浏览器中访问Eureka主界面 http://localhost:8761/
2.2 Eureka Client
Eureka Client引用项：
◊ spring-cloud-starter-netflix-eureka-client
◊ spring-boot-starter-web
<?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>priv.libing</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>libing</groupId> <artifactId>libing-eureka</artifactId> <version>0.0.1-SNAPSHOT</version> </parent> <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-web</artifactId> </dependency> </dependencies> </project>
application.yml：
eureka:
client:
service-url:
default-zone: http://locahost:8761/eureka/
server:
port: 8762
spring:
application:
name: eureka-client
EurekaClientApplication.java：
package priv.libing.eurekaclient; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.netflix.eureka.EnableEurekaClient; @EnableEurekaClient @SpringBootApplication public class EurekaClientApplication { public static void main(String[] args) { SpringApplication.run(EurekaClientApplication.class, args); } }
其中，注解@EnableEurekaClient开启Eureka Client功能。
启动运行eureka-server及eureka-client：
以上示例代码：libing-eureka.zip
3. Eureka Server集群
在实际项目中，微服务实例较多，需要对Eureka Server进行高可用集群。
本地搭建Eureka Server集群，修改C:\Windows\System32\drivers\etc\hosts
127.0.0.1 slave1 127.0.0.1 slave2
eureka-server调整结构：
application.yml：
spring:
application:
name: eureka-server
application-slave1.yml：
server:
port: 8761
eureka:
instance:
hostname: slave1
client:
service-url:
default-zone: http://slave2:8762/eureka/
application-slave2.yml：
server:
port: 8762
eureka:
instance:
hostname: slave2
client:
service-url:
default-zone: http://slave1:8761/eureka/
eureka-client项目application.yml：
eureka:
client:
service-url:
default-zone: http://slave1:8761/eureka/, http://slave2:8762/eureka/
server:
port: 8763
spring:
application:
name: eureka-client
（1）eureka-server运行：mvn:package
java -jar F:\eureka-server-0.0.1-SNAPSHOT.jar --spring.profiles.active=slave1
java -jar F:\eureka-server-0.0.1-SNAPSHOT.jar --spring.profiles.active=slave2
（2）eureka-server运行：IDEA配置一个项目多实例
Single instance only：取消勾选
Active profiles：slave1或slave2，分别配置，运行两个实例。
以上示例代码：libing-eureka-slave.zip
