SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan

莫问天涯路几重,轻衫侧帽且从容。这篇文章主要讲述SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan相关的知识,希望能为你提供帮助。

SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan

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经过上一节的详细分析,我们知道可以通过 LoadBalancerClientFactory 知道默认配置类为 LoadBalancerClientConfiguration. 并且获取微服务名称可以通过 environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
[LoadBalancerClientFactory]()
public static final String NAMESPACE = "loadbalancer"; public static final String PROPERTY_NAME = NAMESPACE + ".client.name"; public LoadBalancerClientFactory() { super(LoadBalancerClientConfiguration.class, NAMESPACE, PROPERTY_NAME); }

【SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan】查看配置类 LoadBalancerClientConfiguration,我们可以发现这个类主要定义两种 Bean,分别是 ReactorLoadBalancer& lt; ServiceInstance& gt; ServiceInstanceListSupplier
ReactorLoadBalancer 是负载均衡器,主要提供根据服务名称获取服务实例列表并从从中选择的功能。
[ReactorLoadBalancer]()
Mono< Response< T> > choose(Request request);

在默认配置中的实现是:
[LoadBalancerClientConfiguration]()
@Bean @ConditionalOnMissingBean public ReactorLoadBalancer< ServiceInstance> reactorServiceInstanceLoadBalancer( Environment environment, LoadBalancerClientFactory loadBalancerClientFactory) { //获取微服务名称 String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME); //创建 RoundRobinLoadBalancer //注意这里注入的是 LazyProvider,这主要因为在注册这个 Bean 的时候相关的 Bean 可能还没有被加载注册,利用 LazyProvider 而不是直接注入所需的 Bean 防止报找不到 Bean 注入的错误。 return new RoundRobinLoadBalancer(loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name); }

可以看出,默认配置的 ReactorLoadBalancer 实现是 RoundRobinLoadBalancer。这个负载均衡器实现很简单,有一个原子类型的 AtomicInteger position,从 ServiceInstanceListSupplier 中读取所有的服务实例列表,然后对于 position 原子加1,对列表大小取模,返回列表中这个位置的服务实例 ServiceInstance
[RoundRobinLoadBalancer]()
public Mono< Response< ServiceInstance> > choose(Request request) { //注入的时候注入的是 Lazy Provider,这里取出真正的 Bean,也就是 ServiceInstanceListSupplier ServiceInstanceListSupplier supplier = serviceInstanceListSupplierProvider .getIfAvailable(NoopServiceInstanceListSupplier::new); //获取实例列表 return supplier.get(request) .next() //从列表中选择一个实例 .map(serviceInstances -> processInstanceResponse(supplier, serviceInstances)); }private Response< ServiceInstance> processInstanceResponse(ServiceInstanceListSupplier supplier, List< ServiceInstance> serviceInstances) { Response< ServiceInstance> serviceInstanceResponse = getInstanceResponse(serviceInstances); // 如果 ServiceInstanceListSupplier 也实现了 SelectedInstanceCallback,则执行下面的逻辑进行回调。SelectedInstanceCallback 就是每次负载均衡器选择实例之后进行的回调 if (supplier instanceof SelectedInstanceCallback & & serviceInstanceResponse.hasServer()) { ((SelectedInstanceCallback) supplier).selectedServiceInstance(serviceInstanceResponse.getServer()); } return serviceInstanceResponse; }private Response< ServiceInstance> getInstanceResponse(List< ServiceInstance> instances) { if (instances.isEmpty()) { return new EmptyResponse(); } //postion 原子 +1 并取绝对值 int pos = Math.abs(this.position.incrementAndGet()); //返回对应下标的实例 ServiceInstance instance = instances.get(pos % instances.size()); return new DefaultResponse(instance); }

ServiceInstanceListSupplier 是服务列表提供者接口:
[ServiceInstanceListSupplier]()
public interface ServiceInstanceListSupplier extends Supplier< Flux< List< ServiceInstance> > > { String getServiceId(); default Flux< List< ServiceInstance> > get(Request request) { return get(); } static ServiceInstanceListSupplierBuilder builder() { return new ServiceInstanceListSupplierBuilder(); } }

spring-cloud-loadbalancer 中有很多 ServiceInstanceListSupplier 的实现,在默认配置中是通过属性配置指定实现的,这个配置项是spring.cloud.loadbalancer.configurations。例如:
[LoadBalancerClientConfiguration]()
@Bean @ConditionalOnBean(ReactiveDiscoveryClient.class) @ConditionalOnMissingBean //spring.cloud.loadbalancer.configurations 未指定或者为 default @ConditionalOnProperty(value = "https://www.songbingjia.com/android/spring.cloud.loadbalancer.configurations", havingValue = "https://www.songbingjia.com/android/default", matchIfMissing = true) public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier( ConfigurableApplicationContext context) { return ServiceInstanceListSupplier.builder() //通过 DiscoveryClient 提供实例 .withDiscoveryClient() //开启缓存 .withCaching() .build(context); }@Bean @ConditionalOnBean(ReactiveDiscoveryClient.class) @ConditionalOnMissingBean //如果 spring.cloud.loadbalancer.configurations 指定为 zone-preference @ConditionalOnProperty(value = "https://www.songbingjia.com/android/spring.cloud.loadbalancer.configurations", havingValue = "https://www.songbingjia.com/android/zone-preference") public ServiceInstanceListSupplier zonePreferenceDiscoveryClientServiceInstanceListSupplier( ConfigurableApplicationContext context) { return ServiceInstanceListSupplier.builder() //通过 DiscoveryClient 提供实例 .withDiscoveryClient() //启用更倾向于同一个 zone 下实例的特性 .withZonePreference() //开启缓存 .withCaching() .build(context); }

可以看到,可以通过 ServiceInstanceListSupplier.builder() 生成官方封装好各种特性的 ServiceInstanceListSupplier。其实从底层实现可以看出,所有的 ServiceInstanceListSupplier 实现都是代理模式,例如对于默认配置,底层代码近似于:
return//开启服务实例缓存 new CachingServiceInstanceListSupplier( //启用通过 discoveryClient 的服务发现 new DiscoveryClientServiceInstanceListSupplier( discoveryClient, env ) , cacheManagerProvider.getIfAvailable() );

除了默认配置 LoadBalancerClientConfiguration,用户配置自定义配置则是通过 @LoadBalancerClients@LoadBalancerClient.这个原理是通过 LoadBalancerClientConfigurationRegistrar 实现的。首先,我们来看一下 LoadBalancerClientFactory 这个 NamedContextFactory 是如何创建的:
[LoadBalancerAutoConfiguration]
private final ObjectProvider< List< LoadBalancerClientSpecification> > configurations; public LoadBalancerAutoConfiguration(ObjectProvider< List< LoadBalancerClientSpecification> > configurations) { //注入 LoadBalancerClientSpecification List 的 provider //在 Bean 创建的时候,进行载入,而不是注册的时候 this.configurations = configurations; }@ConditionalOnMissingBean @Bean public LoadBalancerClientFactory loadBalancerClientFactory() { //创建 LoadBalancerClientFactory LoadBalancerClientFactory clientFactory = new LoadBalancerClientFactory(); //读取所有的 LoadBalancerClientSpecification,设置为 LoadBalancerClientFactory 的配置 clientFactory.setConfigurations(this.configurations.getIfAvailable(Collections::emptyList)); return clientFactory; }

那么,LoadBalancerClientSpecification 这些 Bean 是怎么创建的呢?在 @LoadBalancerClients@LoadBalancerClient 注解中,都包含 @Import(LoadBalancerClientConfigurationRegistrar.class)。这个 @Import 加载一个 ImportBeanDefinitionRegistrar,这里是 LoadBalancerClientConfigurationRegistrar. ImportBeanDefinitionRegistrar里面的方法参数包含注解元数据,以及注册 Bean 的 BeanDefinitionRegistry。一般通过注解元数据,动态通过 BeanDefinitionRegistry 注册 Bean,在这里的实现是:
[LoadBalancerClients]
@Configuration(proxyBeanMethods = false) @Retention(RetentionPolicy.RUNTIME) @Target({ ElementType.TYPE }) @Documented @Import(LoadBalancerClientConfigurationRegistrar.class) public @interface LoadBalancerClients { //可以指定多个 LoadBalancerClient LoadBalancerClient[] value() default {}; //指定所有的负载均衡配置的默认配置 Class< ?> [] defaultConfiguration() default {}; }

[LoadBalancerClient]
@Configuration(proxyBeanMethods = false) @Import(LoadBalancerClientConfigurationRegistrar.class) @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface LoadBalancerClient { //name 和 value 都是微服务名称 @AliasFor("name") String value() default ""; @AliasFor("value") String name() default ""; //这个微服务的配置 Class< ?> [] configuration() default {}; }

[LoadBalancerClientConfigurationRegistrar]
@Override public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) { //获取 LoadBalancerClients 注解的元数据 Map< String, Object> attrs = metadata.getAnnotationAttributes(LoadBalancerClients.class.getName(), true); if (attrs != null & & attrs.containsKey("value")) { AnnotationAttributes[] clients = (AnnotationAttributes[]) attrs.get("value"); //对于 value 属性,其实就是一个 LoadBalancerClient 列表,对于每个生成一个特定微服务名字的LoadBalancerClientSpecification for (AnnotationAttributes client : clients) { registerClientConfiguration(registry, getClientName(client), client.get("configuration")); } } //如果指定了 defaultConfiguration,则注册为 default 的配置 if (attrs != null & & attrs.containsKey("defaultConfiguration")) { String name; if (metadata.hasEnclosingClass()) { name = "default." + metadata.getEnclosingClassName(); } else { name = "default." + metadata.getClassName(); } registerClientConfiguration(registry, name, attrs.get("defaultConfiguration")); } //获取 LoadBalancerClient 注解的元数据 Map< String, Object> client = metadata.getAnnotationAttributes(LoadBalancerClient.class.getName(), true); String name = getClientName(client); if (name != null) { registerClientConfiguration(registry, name, client.get("configuration")); } }private static void registerClientConfiguration(BeanDefinitionRegistry registry, Object name, Object configuration) { //初始化 LoadBalancerClientSpecification 的 BeanDefinition,用于注册一个 LoadBalancerClientSpecification Bean BeanDefinitionBuilder builder = BeanDefinitionBuilder .genericBeanDefinition(LoadBalancerClientSpecification.class); //构造器参数 builder.addConstructorArgValue(name); builder.addConstructorArgValue(configuration); //注册 Bean registry.registerBeanDefinition(name + ".LoadBalancerClientSpecification", builder.getBeanDefinition()); }

从代码中我们可以看出,通过使用 @LoadBalancerClients@LoadBalancerClient 注解可以自动生成对应的 LoadBalancerClientSpecification 进而实现公共负载均衡配置或者特定某个微服务的负载均衡配置。
SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan

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我们这一节详细分析 Spring Cloud LoadBalancer 的源代码来理解其中的原理,下一节我们将介绍在我们项目中使用 Spring Cloud LoadBalancer 要实现的功能。
SpringCloud升级之路2020.0.x版-22.Spring Cloud LoadBalan

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