Eureka【支持Remote Region】

工程公共pom依赖

<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>

<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>

1、eureka server工程

1.1、eureka server工程pom依赖：

<!--加上文章头部的公共依赖-->

<dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
        </dependency>
</dependencies>

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

1.2、项目启动类：

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

@SpringBootApplication
@EnableEurekaServer
public class EurkeaServerApplication {

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

1.3、这里配置4个eureka server实例，路径：eureka-serversrcmain esources，分4个zone，属于region-east、region-west两个区。

属于region-east的配置文件为：application-zone1.yml，application-zone2.yml

application-zone1.yml：

server:
  port: 8761
spring:
  application:
    name: eureka-server
eureka:
  server:
    waitTimeInMsWhenSyncEmpty: 0
    enableSelfPreservation: false
    remoteRegionUrlsWithName:
      region-west: http://localhost:8763/eureka/
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-east
    service-url:
      zone1: http://localhost:8761/eureka/
      zone2: http://localhost:8762/eureka/
    availability-zones:
      region-east: zone1,zone2
  instance:
    hostname: localhost
    metadataMap.zone: zone1

application-zone2.yml：

server:
  port: 8762
spring:
  application:
    name: eureka-server
eureka:
  server:
    waitTimeInMsWhenSyncEmpty: 0
    enableSelfPreservation: false
    remoteRegionUrlsWithName:
      region-west: http://localhost:8763/eureka/
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-east
    service-url:
      zone1: http://localhost:8761/eureka/
      zone2: http://localhost:8762/eureka/
    availability-zones:
      region-east: zone1,zone2
  instance:
    hostname: localhost
    metadataMap.zone: zone2

属于region-west的配置文件为：application-zone3-region-west.yml，application-zone4-region-west.yml

application-zone3-region-west.yml

server:
  port: 8763
spring:
  application:
    name: eureka-server
eureka:
  server:
    waitTimeInMsWhenSyncEmpty: 0
    enableSelfPreservation: false
    remoteRegionUrlsWithName:
      region-east: http://localhost:8761/eureka/
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-west
    service-url:
      zone3: http://localhost:8763/eureka/
      zone4: http://localhost:8764/eureka/
    availability-zones:
      region-west: zone3,zone4
  instance:
    hostname: localhost
    metadataMap.zone: zone3

application-zone4-region-west.yml

server:
  port: 8764
spring:
  application:
    name: eureka-server
eureka:
  server:
    waitTimeInMsWhenSyncEmpty: 0
    enableSelfPreservation: false
    remoteRegionUrlsWithName:
      region-east: http://localhost:8761/eureka/
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-west
    service-url:
      zone3: http://localhost:8763/eureka/
      zone4: http://localhost:8764/eureka/
    availability-zones:
      region-west: zone3,zone4
  instance:
    hostname: localhost
    metadataMap.zone: zone4

由于框架中，EurekaServerConfigBean的remoteRegionAppWhitelist默认值是null，而getRemoteRegionAppWhitelist(String regionName)方法又被直接调用，如果工程上不处理，就直接空指针异常了。

//框架源码
package org.springframework.cloud.netflix.eureka.server;

import ......

@ConfigurationProperties("eureka.server")
public class EurekaServerConfigBean implements EurekaServerConfig {
    public static final String PREFIX = "eureka.server";
    private static final int MINUTES = 60000;
    @Autowired(
        required = false
    )
    PropertyResolver propertyResolver;
    private String aWSAccessId;
    //.....private String[] remoteRegionUrls;
    private Map<String, Set<String>> remoteRegionAppWhitelist;
　　//......
}

so，在eureka server工程中加入以下配置：

import com.netflix.discovery.EurekaClientConfig;
import com.netflix.eureka.EurekaServerConfig;
import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.cloud.netflix.eureka.server.EurekaServerAutoConfiguration;
import org.springframework.cloud.netflix.eureka.server.EurekaServerConfigBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.HashMap;

/**
 * 配置类
 */
@Configuration
@AutoConfigureBefore(EurekaServerAutoConfiguration.class)//当前配置类EurekaServerAutoConfiguration加载完毕后的后续加载操作
public class RegionConfig {

    @Bean
    @ConditionalOnMissingBean
    public EurekaServerConfig eurekaServerConfig(EurekaClientConfig clientConfig) {
        EurekaServerConfigBean server = new EurekaServerConfigBean();
        if (clientConfig.shouldRegisterWithEureka()) {
            server.setRegistrySyncRetries(5);
        }
        server.setRemoteRegionAppWhitelist(new HashMap<>());
        return server;
    }
}

1.4、启动实例，执行命令：

mvn spring-boot:run -Dspring.profiles.active=zone1
mvn spring-boot:run -Dspring.profiles.active=zone2
mvn spring-boot:run -Dspring.profiles.active=zone3-region-west
mvn spring-boot:run -Dspring.profiles.active=zone4-region-west

2、Eureka Client工程

2.1、eureka client工程pom依赖：

<!--加上文章头部公共依赖-->

<dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
</dependencies>

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

2.2、eureka client工程启动类：

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

@SpringBootApplication
@EnableDiscoveryClient
public class EurekaClientApplication {

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

2.3、eureka client工程配置文件

这里配置4个client实例，也是分4个zone，属于region-east、region-west两个区。 

属于region-east的配置文件为：application-zone1.yml，application-zone2.yml

application-zone1.yml：

server:
  port: 8071
spring:
  application.name: demo-client
eureka:
  client:
    prefer-same-zone-eureka: true
    region: region-east
    service-url:
      zone1: http://localhost:8761/eureka/
      zone2: http://localhost:8762/eureka/
    availability-zones:
      region-east: zone1,zone2
  instance:
    metadataMap.zone: zone1

application-zone2.yml

server:
  port: 8072
spring:
  application.name: demo-client
eureka:
  client:
    prefer-same-zone-eureka: true
    region: region-east
    service-url:
      zone1: http://localhost:8761/eureka/
      zone2: http://localhost:8762/eureka/
    availability-zones:
      region-east: zone1,zone2
  instance:
    metadataMap.zone: zone2

属于region-west的配置文件为：application-zone3.yml，application-zone4.yml

application-zone3.yml：

server:
  port: 8073
spring:
  application.name: demo-client
eureka:
  client:
    prefer-same-zone-eureka: true
    region: region-west
    service-url:
      zone3: http://localhost:8763/eureka/
      zone4: http://localhost:8764/eureka/
    availability-zones:
      region-west: zone3,zone4
  instance:
    metadataMap.zone: zone3

application-zone4.yml：

server:
  port: 8074
spring:
  application.name: demo-client
eureka:
  client:
    prefer-same-zone-eureka: true
    region: region-west
    service-url:
      zone3: http://localhost:8763/eureka/
      zone4: http://localhost:8764/eureka/
    availability-zones:
      region-west: zone3,zone4
  instance:
    metadataMap.zone: zone4

application.yml：

management:
  endpoints:
    web:
      exposure:
        include: '*'

2.4、启动eureka client工程，执行命令：

mvn spring-boot:run -Dspring.profiles.active=zone1
mvn spring-boot:run -Dspring.profiles.active=zone2
mvn spring-boot:run -Dspring.profiles.active=zone3
mvn spring-boot:run -Dspring.profiles.active=zone4

3、Zuul Gateway工程

3.1、zuul gateway工程pom依赖：

<!--加上文章头部的公共依赖--> 

<dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-zuul</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
        </dependency>
</dependencies>

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

3.2、zuul gateway工程启动类：

package cn.springcloud.book;

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

@SpringBootApplication
@EnableZuulProxy
@EnableDiscoveryClient
public class ZuulGatewayApplication {

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

3.3、zuul gateway工程配置文件，这里使用2个gateway实例来演示fallback到remote region的应用实例功能，配置文件一个属于region-east，一个属于region-west。

application.yml：

spring:
  application:
    name: zuul-gateway
management:
  endpoints:
    web:
      exposure:
        include: '*'

application-zone1.yml：

server:
  port: 10001
eureka:
  instance:
    metadataMap.zone: zone1
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-east
    service-url:
      zone1: http://localhost:8761/eureka/
      zone2: http://localhost:8762/eureka/
    availability-zones:
      region-east: zone1,zone2

application-zone3-region-west.yml：

server:
  port: 10002
eureka:
  instance:
    metadataMap.zone: zone3
  client:
    register-with-eureka: true
    fetch-registry: true
    region: region-west
    service-url:
      zone3: http://localhost:8763/eureka/
      zone4: http://localhost:8764/eureka/
    availability-zones:
      region-west: zone3,zone4

3.4、启动gateway工程，执行命令：

mvn spring-boot:run -Dspring.profiles.active=zone1
mvn spring-boot:run -Dspring.profiles.active=zone3-region-west

访问：localhost:10001/demo-client/actuator/env，结果如下：

 访问：localhost:10002/demo-client/actuator/env，结果如下：

 可以看到ZoneAffinity特性（上一篇文章有讲），zone1的gateway访问的是zone1的demo-client，zone3的gateway访问的是zone3的demo-client。

接下来，关闭eureka-client的zone1实例，继续访问 localhost:10001/demo-client/actuator/env，可以看到在经过几个错误之后，自动fallback到了remote-region的zone4实例上，实现了类似异地多活自动转移请求的效果。