浅谈Spring Cloud Ribbon的原理

网友投稿 241 2023-02-16


浅谈Spring Cloud Ribbon的原理

Ribbon是Netflix发布的开源项目,主要功能是提供客户端的软件负载均衡算法,将Netflix的中间层服务连接在一起。Ribbon客户端组件提供一系列完善的配置项如连接超时,重试等。简单的说,就是在配置文件中列出Load Balancer(简称LB)后面所有的机器,Ribbon会自动的帮助你基于某种规则(如简单轮询,随即连接等)去连接这些机器。我们也很容易使用Ribbon实现自定义的负载均衡算法。

说起负载均衡一般都会想到服务端的负载均衡,常用产品包括LBS硬件或云服务、Nginx等,都是耳熟能详的产品。

而Spring Cloud提供了让服务调用端具备负载均衡能力的Ribbon,通过和Eureka的紧密结合,不用在服务集群内再架设负载均衡服务,很大程度简化了服务集群内的架构。

具体也不想多写虚的介绍,反正哪里都能看得到相关的介绍。

直接开撸代码,通过代码来看Ribbon是如何实现的。

配置

详解:

1.RibbonAutoConfiguration配置生成RibbonLoadBalancerClient实例。

代码位置:

spring-cloud-netflix-core-1.3.5.RELEASE.jar

org.springframework.cloud.netflix.ribbon

RibbonAutoConfiguration.class

@Configuration

@ConditionalOnClass({ IClient.class, RestTemplate.class, AsyncRestTemplate.class, Ribbon.class})

@RibbonClients

@AutoConfigureAfter(name = "org.springframework.cloud.netflix.eureka.EurekaClientAutoConfiguration")

@AutoConfigureBefore({LoadBalancerAutoConfiguration.class, AsyncLoadBalancerAutoConfiguration.class})

@EnableConfigurationProperties(RibbonEagerLoadProperties.class)

public class RibbonAutoConfiguration {

// 略

@Bean

@ConditionalOnMissingBean(LoadBalancerClient.class)

public LoadBalancerClient loadBalancerClient() {

return new RibbonLoadBalancerClient(springClientFactory());

}

// 略

}

先看配置条件项,RibbonAutoConfiguration配置必须在LoadBalancerAutoConfiguration配置前执行,因为在LoadBalancerAutoConfiguration配置中会使用RibbonLoadBalancerClient实例。

RibbonLoadBalancerClient继承自LoadBalancerClient接口,是负载均衡客户端,也是负载均衡策略的调用方。

2.LoadBalancerInterceptorConfig配置生成:

1).负载均衡拦截器LoadBalancerInterceptor实例

包含:

LoadBalancerClient实现类的RibbonLoadBalancerClient实例

负载均衡的请求创建工厂LoadBalancerRequestFactory:实例

2).RestTemplate自定义的RestTemplateCustomizer实例

代码位置:

spring-cloud-commons-1.2.4.RELEASE.jar

org.springframework.cloud.client.loadbalancer

LoadBalancerAutoConfiguration.class

@Configuration

@ConditionalOnClass(RestTemplate.class)

@ConditionalOnBean(LoadBalancerClient.class)

@EnableConfigurationProperties(LoadBalancerRetryProperties.class)

public class LoadBalancerAutoConfiguration {

// 略

@Bean

@ConditionalOnMissingBean

public LoadBalancerRequestFactory loadBalancerRequestFactory(

LoadBalancerClient loadBalancerClient) {

return new LoadBalancerRequestFactory(loadBalancerClient, transformers);

}

@Configuration

@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")

static class LoadBalancerInterceptorConfig {

@Bean

public LoadBalancerInterceptor ribbonInterceptor(

LoadBalancerClient loadBalancerClient,

LoadBalancerRequestFactory requestFactory) {

return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);

}

@Bean

@ConditionalOnMissingBean

public RestTemplateCustomizer restTemplateCustomizer(

final LoadBalancerInterceptor loadBalancerInterceptor) {

return new RestTemplateCustomizer() {

@Override

public void customize(RestTemplate restTemplate) {

List list = new ArrayList<>(

restTemplate.getInterceptors());

list.add(loadBalancerInterceptor);

restTemplate.setInterceptors(list);

}

};

}

}

// 略

}

先看配置条件项:

要求在项目环境中必须要有RestTemplate类。

要求必须要有LoadBalancerClient接口的实现类的实例,也就是上一步生成的RibbonLoadBalancerClient。

3.通过上面一步创建的RestTemplateCustomizer配置所有RestTemplate实例,就是将负载均衡拦截器设置给RestTemplate实例。

@Configuration

@ConditionalOnClass(RestTemplate.class)

@ConditionalOnBean(LoadBalancerClient.class)

@EnableConfigurationProperties(LoadBalancerRetryProperties.class)

public class LoadBalancerAutoConfiguration {

// 略

@Bean

public SmartInitializingSingleton loadBalancedRestTemplateInitializer(

final List customizers) {

return http://new SmartInitializingSingleton() {

@Override

public void afterSingletonsInstantiated() {

for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {

for (RestTemplateCustomizer customizer : customizers) {

customizer.customize(restTemplate);

}

}

}

};

}

// 略

@Configuration

@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")

static class LoadBalancerInterceptorConfig {

@Bean

public LoadBalancerInterceptor ribbonInterceptor(

LoadBalancerClient loadBalancerClient,

LoadBalancerRequestFactory requestFactory) {

return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);

}

@Bean

@ConditionalOnMissingBean

public RestTemplateCustomizer restTemplateCustomizer(

final LoadBalancerInterceptor loadBalancerInterceptor) {

return new RestTemplateCustomizer() {

@Override

public void customize(RestTemplate restTemplate) {

List list = new ArrayList<>(

restTemplate.getInterceptors());

list.add(loadBalancerInterceptor);

restTemplate.setInterceptors(list);

}

};

}

}

// 略

}

restTemplate.setInterceptors(list)这个地方就是注入负载均衡拦截器的地方LoadBalancerInterceptor。

从这个地方实际上也可以猜出来,RestTemplate可以通过注入的拦截器来构建相应的请求实现负载均衡。

也能看出来可以自定义拦截器实现其他目的。

4.RibbonClientConfiguration配置生成ZoneAwareLoadBalancer实例

代码位置:

spring-cloud-netflix-core-1.3.5.RELEASE.jar

org.springframework.cloud.netflix.ribbon

RibbonClientConfiguration.class

@SuppressWarnings("deprecation")

@Configuration

@EnableConfigurationProperties

//Order is important here, last should be the default, first should be optional

// see https://github.com/spring-cloud/spring-cloud-netflix/issues/2086#issuecomment-316281653

@Import({OkHttpRibbonConfiguration.class, RestClientRibbonConfiguration.class, HttpClientRibbonConfiguration.class})

public class RibbonClientConfiguration {

// 略

@Bean

@ConditionalOnMissingBean

public ILoadBalancer ribbonLoadBalancer(IClientConfig config,

ServerList serverList, ServerListFilter 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);

}

// 略

}

ZoneAwareLoadBalancer继承自ILoadBalancer接口,该接口有一个方法:

/**

* Choose a server from load balancer.

*

* @param key An object that the load balancer may use to determine which server to return. null if

* the load balancer does not use this parameter.

* @return server chosen

*/

public Server chooseServer(Object key);

ZoneAwareLoadBalancer就是一个具体的负载均衡实现类,也是默认的负载均衡类,通过对chooseServer方法的实现选取某个服务实例。

拦截&请求

1.使用RestTemplate进行Get、Post等各种请求,都是通过doExecute方法实现

代码位置:

spring-web-4.3.12.RELEASE.jar

org.springframework.web.client

RestTemplate.class

public class RestTemplate extends InterceptingHttpAccessor implements RestOperations {

// 略

protected T doExecute(URI url, HttpMethod method, RequestCallback requestCallback,

ResponseExtractor responseExtractor) throws RestClientException {

Assert.notNull(url, "'url' must not be null");

Assert.notNull(method, "'method' must not be null");

ClientHttpResponse response = null;

try {

ClientHttpRequest request = createRequest(url, method);

if (requestCallback != null) {

requestCallback.doWithRequest(request);

}

response = request.execute();

handleResponse(url, method, response);

if (responseExtractor != null) {

return responseExtractor.extractData(response);

}

else {

return null;

}

}

catch (IOException ex) {

String resource = url.toString();

String query = url.getRawQuery();

resource = (query != null ? resource.substring(0, resource.indexOf('?')) : resource);

throw new ResourceAccessException("I/O error on " + method.name() +

" request for \"" + resource + "\": " + ex.getMessage(), ex);

}

finally {

if (response != null) {

response.close();

}

}

}

// 略

}

支持的各种http请求方法最终都是调用doExecute方法,该方法内调用创建方法创建请求实例,并执行请求得到响应对象。

2.生成请求实例创建工厂

上一步代码中,调用createRequest方法创建请求实例,这个方法是定义在父类中。

先整理出主要的继承关系:

createRequest方法实际是定义在HttpAccessor抽象类中。

public abstract class HttpAccessor {

private ClientHttpRequestFactory requestFactory = new SimpleClientHttpRequestFactory();

public void setRequestFactory(ClientHttpRequestFactory requestFactory) {

Assert.notNull(requestFactory, "ClientHttpRequestFactory must not be null");

this.requestFactory = requestFactory;

}

public ClientHttpRequestFactory getRequestFactory() {

return this.requestFactory;

}

protected ClientHttpRequest createRequest(URI url, HttpMethod method) throws IOException {

ClientHttpRequest request = getRequestFactory().createRequest(url, method);

if (logger.isDebugEnabled()) {

logger.debug("Created " + method.name() + " request for \"" + url + "\"");

}

return request;

}

}

在createRequest方法中调用getRequestFactory方法获得请求实例创建工厂,实际上getRequestFactory并不是当前HttpAccessor类中定义的,而是在子类InterceptingHttpAccessor中定义的。

public abstract class InterceptingHttpAccessor extends HttpAccessor {

private List interceptors = new ArrayList();

public void setInterceptors(List interceptors) {

this.interceptors = interceptors;

}

public List getInterceptors() {

return interceptors;

}

@Override

public ClientHttpRequestFactory getRequestFactory() {

ClientHttpRequestFactory delegate = super.getRequestFactory();

if (!CollectionUtils.isEmpty(getInterceptors())) {

return new InterceptingClientHttpRequestFactory(delegate, getInterceptors());

}

else {

return delegate;

}

}

}

在这里做了个小动作,首先还是通过HttpAccessor类创建并获得SimpleClientHttpRequestFactory工厂,这个工厂主要就是在没有拦截器的时候创建基本请求实例。

其次,在有拦截器注入的情况下,创建InterceptingClientHttpRequestFactory工厂,该工厂就是创建带拦截器的请求实例,因为注入了负载均衡拦截器,所以这里就从InterceptingClientHttpRequestFactory工厂创建。

3.通过工厂创建请求实例

创建实例就看工厂的createRequest方法。

public class InterceptingClientHttpRequestFactory extends AbstractClientHttpRequestFactoryWrapper {

private final List interceptors;

public InterceptingClientHttpRequestFactory(ClientHttpRequestFactory requestFactory,

List interceptors) {

super(requestFactory);

this.interceptors = (interceptors != null ? interceptors : Collections.emptyList());

}

@Override

protected ClientHttpRequest createRequest(URI uri, HttpMethod httpMethod, ClientHttpRequestFactory requestFactory) {

return new InterceptingClientHttpRequest(requestFactory, this.interceptors, uri, httpMethod);

}

}

就是new了个InterceptingClientHttpRequest实例,并且把拦截器、基本请求实例创建工厂注进去。

4.请求实例调用配置阶段注入的负载均衡拦截器的拦截方法intercept

可从第1步看出,创建完请求实例后,通过执行请求实例的execute方法执行请求。

ClientHttpRequest request = createRequest(url, method);

if (requestCallback != null) {

requestCallback.doWithRequest(request);

}

response = request.execute();

实际请求实例是InterceptingClientHttpRequest,execute实际是在它的父类中。

类定义位置:

spring-web-4.3.12.RELEASE.jar

org.springframework.http.client

InterceptingClientHttpRequest.class

看一下它们的继承关系。

在execute方法中实际调用了子类实现的executeInternal方法。

public abstract class AbstractClientHttpRequest implements ClientHttpRequest {

private final HttpHeaders headers = new HttpHeaders();

private boolean executed = false;

@Override

public final HttpHeaders getHeaders() {

return (this.executed ? HttpHeaders.readOnlyHttpHeaders(this.headers) : this.headers);

}

@Override

public final OutputStream getBody() throws IOException {

assertNotExecuted();

return getBodyInternal(this.headers);

}

@Override

public final ClientHttpResponse execute() throws IOException {

assertNotExecuted();

ClientHttpResponse result = executeInternal(this.headers);

this.executed = true;

return result;

}

protected void assertNotExecuted() {

Assert.state(!this.executed, "ClientHttpRequest already executed");

}

protected abstract OutputStream getBodyInternal(HttpHeaders headers) throws IOException;

protected abstract ClientHttpResponse executeInternal(HttpHeaders headers) throws IOException;

}

其实就是InterceptingClientHttpRequest类的executeInternal方法,其中,又调用了一个执行器InterceptingRequestExecution的execute,通关判断如果有拦截器注入进来过,就调用拦截器的intercept方法。

这里的拦截器实际上就是在配置阶段注入进RestTemplate实例的负载均衡拦截器LoadBalancerInterceptor实例,可参考上面配置阶段的第2步。

class InterceptingClientHttpRequest extends AbstractBufferingClientHttpRequest {

// 略

@Override

protected final ClientHttpResponse executeInternal(HttpHeaders headers, byte[] bufferedOutput) throws IOException {

InterceptingRequestExecution requestExecution = new InterceptingRequestExecution();

return requestExecution.execute(this, bufferedOutput);

}

private class InterceptingRequestExecution implements ClientHttpRequestExecution {

private final Iterator iterator;

public InterceptingRequestExecution() {

this.iterator = interceptors.iterator();

}

@Override

public ClientHttpResponse execute(HttpRequest request, byte[] body) throws IOException {

if (this.iterator.hasNext()) {

ClientHttpRequestInterceptor nextInterceptor = this.iterator.next();

return nextInterceptor.intercept(request, body, this);

}

else {

ClientHttpRequest delegate = requestFactory.createRequest(request.getURI(), request.getMethod());

for (Map.Entry> entry : request.getHeaders().entrySet()) {

List values = entry.getValue();

for (String value : values) {

delegate.getHeaders().add(entry.getKey(), value);

}

}

if (body.length > 0) {

StreamUtils.copy(body, delegate.getBody());

}

return delegate.execute();

}

}

}

}

5.负载均衡拦截器调用负载均衡客户端

在负载均衡拦截器LoadBalancerInterceptor类的intercept方法中,又调用了负载均衡客户端LoadBalancerClient实现类的execute方法。

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

private LoadBalancerClient loadBalancer;

private LoadBalancerRequestFactory requestFactory;

public LoadBalancerInterceptor(LoadBalancerClient loadBalancer, LoadBalancerRequestFactory requestFactory) {

this.loadBalancer = loadBalancer;

this.requestFactory = requestFactory;

}

public LoadBalancerInterceptor(LoadBalancerClient loadBalancer) {

// for backwards compatibility

this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));

}

@Override

public 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));

}

}

在配置阶段的第1步,可以看到实现类是RibbonLoadBalancerClient。

6.负载均衡客户端调用负载均衡策略选取目标服务实例并发起请求

在RibbonLoadBalancerClient的第一个execute方法以及getServer方法中可以看到,实际上是通过ILoadBalancer的负载均衡器实现类作的chooseServer方法选取一个服务,交给接下来的请求对象发起一个请求。

这里的负载均衡实现类默认是ZoneAwareLoadBalancer区域感知负载均衡器实例,其内部通过均衡策略选择一个服务。

ZoneAwareLoadBalancer的创建可以参考配置阶段的第4步。

public class RibbonLoadBalancerClient implements LoadBalancerClient {

@Override

public T execute(String serviceId, LoadBalancerRequest request) throws IOException {

ILoadBalancer loadBalancer = getLoadBalancer(serviceId);

Server server = getServer(loadBalancer);

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);

}

@Override

public T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest request) throws IOException {

Server server = null;

if(serviceInstance instanceof RibbonServer) {

server = ((RibbonServer)serviceInstance).getServer();

}

if (server == null) {

throw new IllegalStateException("No instances available for " + serviceId);

}

RibbonLoadBalancerContext context = this.clientFactory

.getLoadBalancerContext(serviceId);

RibbonStatsRecorder statsRecorder = new RibbonStatsRecorder(context, server);

try {

T returnVal = request.apply(serviceInstance);

statsRecorder.recordStats(returnVal);

return returnVal;

}

// catch IOException and rethrow so RestTemplate behaves correctly

catch (IOException ex) {

statsRecorder.recordStats(ex);

throw ex;

}

catch (Exception ex) {

statsRecorder.recordStats(ex);

ReflectionUtils.rethrowRuntimeException(ex);

}

return null;

}

// 略

protected Server getServer(ILoadBalancer loadBalancer) {

if (loadBalancer == null) {

return null;

}

return loadBalancer.chooseServer("default"); // TODO: better handling of key

}

protected ILoadBalancer getLoadBalancer(String serviceId) {

return this.clientFactory.getLoadBalancer(serviceId);

}

public static class RibbonServer implements ServiceInstance {

private final String serviceId;

private final Server server;

private final boolean secure;

private Map metadata;

public RibbonServer(String serviceId, Server server) {

this(serviceId, server, false, Collections. emptyMap());

}

public RibbonServer(String serviceId, Server server, boolean secure,

Map metadata) {

this.serviceId = serviceId;

this.server = server;

this.secure = secure;

this.metadata = metadata;

}

// 略

}

}

代码撸完,总结下。

普通使用RestTemplate请求其他服务时,内部使用的就是常规的http请求实例发送请求。

为RestTemplate增加了@LoanBalanced 注解后,实际上通过配置,为RestTemplate注入负载均衡拦截器,让负载均衡器选择根据其对应的策略选择合适的服务后,再发送请求。


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