一、系統內置的策略有以下幾種。

?這個負載策略配置說白了就是讓 Ribbon 這個客戶端負載均衡器怎么進行訪問服務提供者列表。是輪流訪問？隨機訪問？權重？等。

Ribbon 的負載均衡策略
策略類?? ?命名?? ?說明
RandomRule?? ?隨機策略?? ?隨機選擇 Server
RoundRobinRule?? ?輪訓策略?? ?按順序循環選擇 Server
RetryRule?? ?重試策略?? ?在一個配置時問段內當選擇 Server 不成功，則一直嘗試選擇一個可用的 Server
BestAvailableRule?? ?最低并發策略?? ?逐個考察 Server，如果 Server 斷路器打開，則忽略，再選擇其中并發連接最低的 Server
AvailabilityFilteringRule?? ?可用過濾策略?? ?過濾掉一直連接失敗并被標記為 circuit tripped 的 Server，過濾掉那些高并發連接的 Server（active connections 超過配置的網值）
ResponseTimeWeightedRule?? ?響應時間加權策略?? ?根據 Server 的響應時間分配權重。響應時間越長，權重越低，被選擇到的概率就越低；響應時間越短，權重越高，被選擇到的概率就越高。這個策略很貼切，綜合了各種因素，如：網絡、磁盤、IO等，這些因素直接影響著響應時間
ZoneAvoidanceRule?? ?區域權衡策略?? ?綜合判斷 Server 所在區域的性能和 Server 的可用性輪詢選擇 Server，并且判定一個 AWS Zone 的運行性能是否可用，剔除不可用的 Zone 中的所有 Server
?

二、示例

1.只要在啟動時創建一個IRule對象，注入容器，即可。因為系統內置的容器需要在真正 發起請求時才會創建，并且判斷系統容器中沒有IRule對象。

?

@SpringBootApplication @Slf4j @EnableDiscoveryClient @RestController public class ConsumeApplication {@AutowiredRestTemplate restTemplate;@Bean@LoadBalancedpublic RestTemplate getRestTemplate(){HttpComponentsClientHttpRequestFactory clientHttpRequestFactory = new HttpComponentsClientHttpRequestFactory();clientHttpRequestFactory.setConnectTimeout(5 * 1000);clientHttpRequestFactory.setReadTimeout(5 * 1000);return new RestTemplate(clientHttpRequestFactory);}@Beanpublic IRule ribbonRule() {return new RandomRule();}public static void main(String[] args) {SpringApplication.run(ConsumeApplication.class, args);}@GetMapping("test")public String getContent(){log.info("發起請求");String ret = restTemplate.getForObject("http://provider/provider",String.class);return ret;}}

2.在創建ribbonLoadBalancer時就會使用最新的RULE

三、在發起調用時觸發RULE的choose方法

?1.源碼? ，這個很簡單，就是隨機取一個實例。

package com.netflix.loadbalancer;import java.util.List; import java.util.Random;import com.netflix.client.config.IClientConfig;/*** A loadbalacing strategy that randomly distributes traffic amongst existing* servers.* * @author stonse* */ public class RandomRule extends AbstractLoadBalancerRule {Random rand;public RandomRule() {rand = new Random();}/*** Randomly choose from all living servers*/@edu.umd.cs.findbugs.annotations.SuppressWarnings(value = "RCN_REDUNDANT_NULLCHECK_OF_NULL_VALUE")public Server choose(ILoadBalancer lb, Object key) {if (lb == null) {return null;}Server server = null;while (server == null) {if (Thread.interrupted()) {return null;}List<Server> upList = lb.getReachableServers();List<Server> allList = lb.getAllServers();int serverCount = allList.size();if (serverCount == 0) {/** No servers. End regardless of pass, because subsequent passes* only get more restrictive.*/return null;}int index = rand.nextInt(serverCount);server = upList.get(index);if (server == null) {/** The only time this should happen is if the server list were* somehow trimmed. This is a transient condition. Retry after* yielding.*/Thread.yield();continue;}if (server.isAlive()) {return (server);}// Shouldn't actually happen.. but must be transient or a bug.server = null;Thread.yield();}return server;}

四、可以針對單個服務自定義IRULE規則。

1.編寫IRULE

package com.net.sample.consume;import com.netflix.client.config.IClientConfig; import com.netflix.loadbalancer.AbstractLoadBalancerRule; import com.netflix.loadbalancer.ILoadBalancer; import com.netflix.loadbalancer.IRule; import com.netflix.loadbalancer.Server;import java.util.List; import java.util.Random;public class FirstRule extends AbstractLoadBalancerRule {public FirstRule() {}/*** Randomly choose from all living servers*/public Server choose(ILoadBalancer lb, Object key) {if (lb == null) {return null;}Server server = null;while (server == null) {if (Thread.interrupted()) {return null;}List<Server> upList = lb.getReachableServers();List<Server> allList = lb.getAllServers();int serverCount = allList.size();if (serverCount == 0) {/** No servers. End regardless of pass, because subsequent passes* only get more restrictive.*/return null;}int index = 0;server = upList.get(index);if (server == null) {/** The only time this should happen is if the server list were* somehow trimmed. This is a transient condition. Retry after* yielding.*/Thread.yield();continue;}if (server.isAlive()) {return (server);}// Shouldn't actually happen.. but must be transient or a bug.server = null;Thread.yield();}return server;}@Overridepublic Server choose(Object key) {return choose(getLoadBalancer(), key);}@Overridepublic void initWithNiwsConfig(IClientConfig clientConfig) {// TODO Auto-generated method stub} }

2.編寫CONFIGIGATION,這個配置類不在程序啟動初始化時加載，而是在請求時，由RIBBON內部的SpringClientFactory的子applicationContext來創建和實例化。

package com.net.sample.consume;import com.netflix.client.config.IClientConfig; import com.netflix.loadbalancer.IRule; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration;import javax.annotation.Resource;@Configuration /** 用來標記使用的注解，方便排除或者引用 **/ @AvoidScan public class RibbonFirstLoadBalancingConfiguration {@Beanpublic IRule ribbonRule() {return new FirstRule();}}

3.啟動類加上，啟動時排除上面的配置的包。RibbonClient針對每個服務端進行單獨的配置，就是configuation實例，由這個內部來創建IRULE,IRuleFilter,ServerList都可以自定義。

@SpringBootApplication @Slf4j @EnableDiscoveryClient @RestController @ComponentScan(excludeFilters = @ComponentScan.Filter(type = FilterType.ANNOTATION,value = AvoidScan.class)) @RibbonClient(name = "provider",configuration = RibbonFirstLoadBalancingConfiguration.class) public class ConsumeApplication {

?4.這里看到進入了我們自定義的IRULE規則選擇服務實例。?

總結

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