簡介: Spring Cloud LoadBalancer詳解和源碼分析
Spring Cloud LoadBalancer目前Spring官方是放在spring-cloud-commons裡,
Spring Cloud最新版本為2021.0.2
Spring Cloud LoadBalancer 官網文檔位址 https://docs.spring.io/spring-cloud-commons/docs/3.1.2/reference/html/#spring-cloud-loadbalancer
Spring Cloud官網文檔位址 https://docs.spring.io/spring-cloud/docs/current/reference/html/
一方面Netflix Ribbon停止更新,Spring Cloud LoadBalancer是Spring Cloud官方自己提供的用戶端負載均衡器,抽象和實作,用來替代Ribbon。
常見負載均衡器分為服務端負載均衡器(如網關層均衡負載)和用戶端層均衡負載。
網關層如硬體層面的F5或軟體層面的LVS、或者nginx等。
用戶端層就如Spring Cloud LoadBalancer,作為一個用戶端去發現更新維護服務清單,自定義服務的均衡負載政策(随機、輪詢、小流量的金絲雀等等)。
Spring Cloud提供了自己的用戶端負載平衡器抽象和實作。對于負載均衡機制,
增加了ReactiveLoadBalancer接口,并提供了基于round-robin輪詢和Random随機的實作。
為了從響應式ServiceInstanceListSupplier中選擇執行個體,需要使用ServiceInstanceListSupplier。目前支援ServiceInstanceListSupplier的基于服務發現的實作,該實作使用類路徑中的發現用戶端從Service Discovery中檢索可用的執行個體。
可以通過如下配置來禁用Spring Cloud LoadBalance
spring:
cloud:
loadbalancer:
enabled: false
入門示例
前面simple-ecommerce項目建立已在父Pom引入三大父依賴,詳細可以看下前面的文章<<SpringCloudAlibaba注冊中心與配置中心之利器Nacos實戰與源碼分析>>,其中Spring Cloud的版本為2021.0.1,
前面文章也已說過,Spring Cloud Alibaba整合在spring-cloud-starter-alibaba-nacos-discovery本身就依賴spring-cloud-loadbalancer。
注意如果是Hoxton之前的版本,預設負載均衡器為Ribbon,需要移除Ribbon引用和增加配置spring.cloud.loadbalancer.ribbon.enabled: false。
如果是在Spring Boot項目中添加下面的啟動器依賴,該starter也包含了Spring Boot Caching and Evictor.
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-loadbalancer</artifactId>
</dependency>
我們使用Spring官方提供了負載均衡的用戶端之一RestTemplate,RestTemplate是Spring提供的用于通路Rest服務的用戶端,RestTemplate提供了多種便捷通路遠端Http服務的方法,能夠大大提高用戶端的編寫效率。預設情況下,RestTemplate預設依賴jdk的HTTP連接配接工具。建立RestTemplateConfig配置類,
标注 @LoadBalanced注解,預設使用的ReactiveLoadBalancer實作是RoundRobinLoadBalancer。
原理:
RestTemplate
Spring Cloud LoadBalancer源碼分析我們先從RestTemplate負載均衡的簡單實作來分析入手,除此之外其支援Spring Web Flux響應式程式設計的實作原理思想也是相同,都是通過用戶端添加攔截器,在攔截器中實作負載均衡。從RestTemplate的源碼中可以知道其繼承自InterceptingHttpAccessor抽象類
而InterceptingHttpAccessor抽象類則提供了一個方法setInterceptors,用于設定攔截器,攔截器需要實作ClientHttpRequestInterceptor接口即可,在實際遠端請求服務端接口之前會先調用攔截器的intercept方法。這裡的攔截器相當于Servlet技術中的Filter功能
// 代碼實作在抽象父類InterceptingHttpAccessor裡
// RestTemplate.InterceptingHttpAccessor#setInterceptors
public void setInterceptors(List<ClientHttpRequestInterceptor> interceptors) {
Assert.noNullElements(interceptors, "'interceptors' must not contain null elements");
// Take getInterceptors() List as-is when passed in here
if (this.interceptors != interceptors) {
this.interceptors.clear();
this.interceptors.addAll(interceptors);
AnnotationAwareOrderComparator.sort(this.interceptors);
}
}
LoadBalancerAutoConfiguration
從官網可以知道Spring Cloud LoadBalancer放在spring-cloud-commons,是以也作為其核心的@LoadBalanced注解也就是由spring-cloud-commons來實作,依據SpringBoot自動裝配的原理先檢視依賴包的實作邏輯,不難發現spring-cloud-commons引入了自動配置類LoadBalancerAutoConfiguration和ReactorLoadBalancerClientAutoConfiguration。
當滿足上述的條件時(@Conditional為條件注解),将自動建立LoadBalancerInterceptor并注入到RestTemplate中。
LoadBalancerLnterceptor
LoadBalancerInterceptor實作了ClientHttpRequestInterceptor接口,是以也實作intercept方法,用于實作負載均衡的攔截處理。
LoadBalancerClient
LoadBalancerClient用于進行負載均衡邏輯,繼承自ServiceInstanceChooser接口,從服務清單中選擇出一個服務位址進行調用。在LoadBalancerClient種存在兩個execute()方法,均是用來執行請求的,reconstructURI()是用來重構URL。
對于LoadBalancerClient接口Spring Cloud LoadBalancer的提供預設實作為BlockingLoadBalancerClient
@SuppressWarnings({ "unchecked", "rawtypes" })
public class BlockingLoadBalancerClient implements LoadBalancerClient {
private final ReactiveLoadBalancer.Factory<ServiceInstance> loadBalancerClientFactory;
/**
* @deprecated in favour of
* {@link BlockingLoadBalancerClient#BlockingLoadBalancerClient(ReactiveLoadBalancer.Factory)}
*/
@Deprecated
public BlockingLoadBalancerClient(LoadBalancerClientFactory loadBalancerClientFactory,
LoadBalancerProperties properties) {
this.loadBalancerClientFactory = loadBalancerClientFactory;
}
public BlockingLoadBalancerClient(ReactiveLoadBalancer.Factory<ServiceInstance> loadBalancerClientFactory) {
this.loadBalancerClientFactory = loadBalancerClientFactory;
}
@Override
public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {
String hint = getHint(serviceId);
LoadBalancerRequestAdapter<T, DefaultRequestContext> lbRequest = new LoadBalancerRequestAdapter<>(request,
new DefaultRequestContext(request, hint));
Set<LoadBalancerLifecycle> supportedLifecycleProcessors = getSupportedLifecycleProcessors(serviceId);
supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStart(lbRequest));
ServiceInstance serviceInstance = choose(serviceId, lbRequest);
// 選擇服務
if (serviceInstance == null) {
supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(
new CompletionContext<>(CompletionContext.Status.DISCARD, lbRequest, new EmptyResponse())));
throw new IllegalStateException("No instances available for " + serviceId);
}
return execute(serviceId, serviceInstance, lbRequest);
}
@Override
public <T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request)
throws IOException {
DefaultResponse defaultResponse = new DefaultResponse(serviceInstance);
Set<LoadBalancerLifecycle> supportedLifecycleProcessors = getSupportedLifecycleProcessors(serviceId);
Request lbRequest = request instanceof Request ? (Request) request : new DefaultRequest<>();
supportedLifecycleProcessors
.forEach(lifecycle -> lifecycle.onStartRequest(lbRequest, new DefaultResponse(serviceInstance)));
try {
T response = request.apply(serviceInstance);
Object clientResponse = getClientResponse(response);
supportedLifecycleProcessors
.forEach(lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.SUCCESS,
lbRequest, defaultResponse, clientResponse)));
return response;
}
catch (IOException iOException) {
supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(
new CompletionContext<>(CompletionContext.Status.FAILED, iOException, lbRequest, defaultResponse)));
throw iOException;
}
catch (Exception exception) {
supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(
new CompletionContext<>(CompletionContext.Status.FAILED, exception, lbRequest, defaultResponse)));
ReflectionUtils.rethrowRuntimeException(exception);
}
return null;
}
private <T> Object getClientResponse(T response) {
ClientHttpResponse clientHttpResponse = null;
if (response instanceof ClientHttpResponse) {
clientHttpResponse = (ClientHttpResponse) response;
}
if (clientHttpResponse != null) {
try {
return new ResponseData(clientHttpResponse, null);
}
catch (IOException ignored) {
}
}
return response;
}
private Set<LoadBalancerLifecycle> getSupportedLifecycleProcessors(String serviceId) {
return LoadBalancerLifecycleValidator.getSupportedLifecycleProcessors(
loadBalancerClientFactory.getInstances(serviceId, LoadBalancerLifecycle.class),
DefaultRequestContext.class, Object.class, ServiceInstance.class);
}
@Override
public URI reconstructURI(ServiceInstance serviceInstance, URI original) {
return LoadBalancerUriTools.reconstructURI(serviceInstance, original);
}
@Override
public ServiceInstance choose(String serviceId) {
return choose(serviceId, REQUEST);
}
// 通過不同的負載均衡用戶端實作選擇不同的服務
@Override
public <T> ServiceInstance choose(String serviceId, Request<T> request) {
ReactiveLoadBalancer<ServiceInstance> loadBalancer = loadBalancerClientFactory.getInstance(serviceId);
if (loadBalancer == null) {
return null;
}
Response<ServiceInstance> loadBalancerResponse = Mono.from(loadBalancer.choose(request)).block();
if (loadBalancerResponse == null) {
return null;
}
return loadBalancerResponse.getServer();
}
private String getHint(String serviceId) {
LoadBalancerProperties properties = loadBalancerClientFactory.getProperties(serviceId);
String defaultHint = properties.getHint().getOrDefault("default", "default");
String hintPropertyValue = properties.getHint().get(serviceId);
return hintPropertyValue != null ? hintPropertyValue : defaultHint;
}
}
LoadBalancerClientFactory
BlockingLoadBalancerClient中持有LoadBalancerClientFactory通過調用其getInstance方法擷取具體的負載均衡用戶端。通過工廠類LoadBalancerClientFactory擷取具體的負載均衡器執行個體,後面的loadBalancer.choose(request)調用其接口choose()方法實作根據負載均衡算法選擇下一個伺服器完成負載均衡,而ReactiveLoadBalancer getInstance(String serviceId) 有預設實作LoadBalancerClientFactory
LoadBalancerClientFactory用戶端實作了不同的負載均衡算法,比如輪詢、随機等。LoadBalancerClientFactory繼承自NamedContextFactory,NamedContextFactory繼承ApplicationContextAware,實作Spring ApplicationContext容器操作。
ReactiveLoadBalancer
ReactiveLoadBalancer負載均衡器實作服務選擇,Spring Cloud Balancer中實作了輪詢RoundRobinLoadBalancer、随機RandomLoadBalancer、NacosLoadBalancer算法。
LoadBalancerClientConfiguration
如果沒有顯式指定負載均衡算法,預設預設值為RoundRobinLoadBalancer
@Bean
@ConditionalOnMissingBean
public ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,
LoadBalancerClientFactory loadBalancerClientFactory) {
String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
return new RoundRobinLoadBalancer(
loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);
}
LoadBalancerRequestFactory
LoadBalancerRequest工廠類調用createRequest方法用于建立LoadBalancerRequest。其内部持有LoadBalancerClient對象也即持有BlockingLoadBalancerClient。
在日常項目中,一般負載均衡都是結合Feign使用,後續我們有時間再來分析Feign整合LoadBalancer的自動配置類FeignLoadBalancerAutoConfiguration的實作
ReactorLoadBalancerClientAutoConfiguration
我們也抛一下基于WebClient的@Loadbalanced的流程的引入,首先聲明負載均衡過濾器ReactorLoadBalancerClientAutoConfiguration是一個自動裝配器類,在項目中引入了 WebClient 和 ReactiveLoadBalancer 類之後,自動裝配流程就開始運作,它會初始化一個實作了 ExchangeFilterFunction 的執行個體,在後面該執行個體将作為過濾器被注入到WebClient。後續流程有興趣再自行研究
自定義負載均衡器
從上面可以知道LoadBalancerClientFactory是建立客戶機、負載均衡器和客戶機配置執行個體的工廠。它根據用戶端名稱建立一個Spring ApplicationContext,并從中提取所需的bean。是以進入到LoadBalancerClientFactory類中,需要去實作它的子接口ReactorServiceInstanceLoadBalancer,因為去擷取負載均衡器執行個體的時候,是通過去容器中查找ReactorServiceInstanceLoadBalancer類型的bean來實作的,可以參照RandomLoadBalancer實作代碼
自定義負載均衡器
從上面可以知道LoadBalancerClientFactory是建立客戶機、負載均衡器和客戶機配置執行個體的工廠。它根據用戶端名稱建立一個Spring ApplicationContext,并從中提取所需的bean。是以進入到LoadBalancerClientFactory類中,需要去實作它的子接口ReactorServiceInstanceLoadBalancer,因為去擷取負載均衡器執行個體的時候,是通過去容器中查找ReactorServiceInstanceLoadBalancer類型的bean來實作的,可以參照RandomLoadBalancer實作代碼