Ribbon负载均衡分析

Ribbon使用

ribbon在使用上非常简单，仅仅只sql教程需要在配置类上加入配置即可

    @Bean@LoadBalancedpublic RestTemplate restTemplate(){return new RestTemplate();}

调用时，直接使用在eureka中注册的服务java基础教程名进行调用，就可以由ribbon来进行负载均衡了

    @GetMapping("/checkAndBegin/{userId}")public Integer findResumeOpenStateEureka(@PathVariable Long userId) {
//        List<ServiceInstance> list = discoveryClient.getInstances("lagou-service-resume");
//        ServiceInstance serviceInstance = list.get(0);
//        String host = serviceInstance.getHost();
//        int port = serviceInstance.getPort();String url = "http://zhao-service-resume/resume/openstate/"+userId;System.out.println("从eureka中获取了请求地址"+url);Integer forObject =restTemplate.getForObject(url, Integer.class);return forObject;}

根据要求，zhao-service-resume项目开启多个，并打印请python基础教程求信息，即可发现负载均衡已经实现
另外目前Ribbon的内置负载均衡策略

目前默认使用的是随机负载均衡RandomRule,默认全局生效，但是可以针对不同c#教程的调用服务设置不同的负载均衡策略

zhao-service-resume:ribbon:NFLoadBalancerRuleClassName:
com.netflix.loadbalancer.RandomRule #负载策略调整

同时，可以自定负载均衡策略vb.net教程并配置

Ribbon源码分析

一般而言，自动装配类就是加载配置的入口。

@Configuration
@Conditional(RibbonAutoConfiguration.RibbonClassesConditions.class)
@RibbonClients
@AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")
@AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})
@EnableConfigurationProperties({RibbonEagerLoadProperties.class, ServerIntrospectorProperties.class})
public class RibbonAutoConfiguration {
}

通过上述配置，我们可以先看看LoadBalancerAutoConfiguration的具体内容

 @LoadBalanced@Autowired(required = false)private List<RestTemplate> restTemplates = Collections.emptyList();

此处将自动注入添加了@LoadBalanced注解的RestTemplate对象
同时还注入了一个RestTemplate的定制器RestTemplateCustomizer

 @Beanpublic SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {return () -> restTemplateCustomizers.ifAvailable(customizers -> {for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {for (RestTemplateCustomizer customizer : customizers) {customizer.customize(restTemplate);}}});}

继续进入RestTemplateCustomizer的定制器代码，我们发现在定制器中加入了一个拦截器

@Configuration@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")static class LoadBalancerInterceptorConfig {@Beanpublic LoadBalancerInterceptor ribbonInterceptor(LoadBalancerClient loadBalancerClient,LoadBalancerRequestFactory requestFactory) {return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);}@Bean@ConditionalOnMissingBeanpublic RestTemplateCustomizer restTemplateCustomizer(final LoadBalancerInterceptor loadBalancerInterceptor) {return restTemplate -> {List<ClientHttpRequestInterceptor> list = new ArrayList<>(restTemplate.getInterceptors());list.add(loadBalancerInterceptor);restTemplate.setInterceptors(list);};}}

ClientHttpRequestInterceptor的拦截具体内容为,根据获取到的请求路径和请求地址进行负载均衡

 @Overridepublic ClientHttpResponse intercept(final HttpRequest request, final byte[] body,final ClientHttpRequestExecution execution) throws IOException {final URI originalUri = request.getURI();String serviceName = originalUri.getHost();Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));}

执行负载均衡的代码

 public <T> T execute(String serviceId, LoadBalancerRequest<T> request, Object hint) throws IOException {ILoadBalancer loadBalancer = getLoadBalancer(serviceId);Server server = getServer(loadBalancer, hint);if (server == null) {throw new IllegalStateException("No instances available for " + serviceId);}RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,serviceId), serverIntrospector(serviceId).getMetadata(server));return execute(serviceId, ribbonServer, request);}

从这段代码可以看出，第一行根据配置，选出相应的负载均衡策略。第二行就是根据相应的负载均衡策略选择一个服务端进行服务请求，达到负载均衡的目的
最后在BaseLoadBalancer中执行了根据不同的策略选择服务的操作

    public Server chooseServer(Object key) {if (counter == null) {counter = createCounter();}counter.increment();if (rule == null) {return null;} else {try {return rule.choose(key);} catch (Exception e) {logger.warn("LoadBalancer [{}]:  Error choosing server for key {}", name, key, e);return null;}}}

考虑完了上面的主逻辑之后，还有一个问题，就是服务列表是什么时候获取到的。
在RibbonAutoConfigration中注入了SpringClientFactory，而SpringClientFactory又注入了RibbonClientConfiguration

 public SpringClientFactory() {super(RibbonClientConfiguration.class, NAMESPACE, "ribbon.client.name");}

RibbonClientConfiguration中进行了注入客户端操作的相关操作，包括负载均衡策略，客户端配置，服务列表等，其中最重要的就是如何获取和更新服务列表

 @ConditionalOnMissingBean@SuppressWarnings("unchecked")public ServerList<Server> ribbonServerList(IClientConfig config) {if (this.propertiesFactory.isSet(ServerList.class, name)) {return this.propertiesFactory.get(ServerList.class, config, name);}ConfigurationBasedServerList serverList = new ConfigurationBasedServerList();serverList.initWithNiwsConfig(config);return serverList;}@Bean@ConditionalOnMissingBeanpublic ServerListUpdater ribbonServerListUpdater(IClientConfig config) {return new PollingServerListUpdater(config);}@Bean@ConditionalOnMissingBeanpublic ILoadBalancer ribbonLoadBalancer(IClientConfig config,ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,IRule rule, IPing ping, ServerListUpdater serverListUpdater) {if (this.propertiesFactory.isSet(ILoadBalancer.class, name)) {return this.propertiesFactory.get(ILoadBalancer.class, config, name);}return new ZoneAwareLoadBalancer<>(config, rule, ping, serverList,serverListFilter, serverListUpdater);}

在ribbonList方法中并未有获取serverList的操作，在ribbonLoadBalancer中进行了使用，那么究竟怎么一回事呢？实际上是在ZoneAwareLoadBalancer的父类DynamicServerListLoadBalancer中进行了重新的赋值并且执行了定时任务进行更新。

    void restOfInit(IClientConfig clientConfig) {boolean primeConnection = this.isEnablePrimingConnections();// turn this off to avoid duplicated asynchronous priming done in BaseLoadBalancer.setServerList()this.setEnablePrimingConnections(false);enableAndInitLearnNewServersFeature();updateListOfServers();if (primeConnection && this.getPrimeConnections() != null) {this.getPrimeConnections().primeConnections(getReachableServers());}this.setEnablePrimingConnections(primeConnection);LOGGER.info("DynamicServerListLoadBalancer for client {} initialized: {}", clientConfig.getClientName(), this.toString());}

首先通过updateAction.doUpdate();更新，然后通过getRefreshExecutor()进行获取

 @Overridepublic synchronized void start(final UpdateAction updateAction) {if (isActive.compareAndSet(false, true)) {final Runnable wrapperRunnable = new Runnable() {@Overridepublic void run() {if (!isActive.get()) {if (scheduledFuture != null) {scheduledFuture.cancel(true);}return;}try {updateAction.doUpdate();lastUpdated = System.currentTimeMillis();} catch (Exception e) {logger.warn("Failed one update cycle", e);}}};scheduledFuture = getRefreshExecutor().scheduleWithFixedDelay(wrapperRunnable,initialDelayMs,refreshIntervalMs,TimeUnit.MILLISECONDS);} else {logger.info("Already active, no-op");}}

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