Spring Cloud - Ribbon

王晗發(fā)布于2019-08-15 13:50 / 653人閱讀

摘要：根據(jù)傳入的從中挑選一個對應(yīng)的。是負載均衡策略實現(xiàn)，默認由生成，根據(jù)來執(zhí)行請求，調(diào)用。將轉(zhuǎn)換成通過注冊中心中各個服務(wù)節(jié)點的初始化流程返回了一個攔截器，作用主要是在客戶端發(fā)起請求時進行攔截，進而實現(xiàn)客戶端負載均衡功能。

@LoadBalanced

public interface ServiceInstanceChooser {
    // 根據(jù)傳入的serviceId從LoadBalancer中挑選一個對應(yīng)的ServiceInstance。
    ServiceInstance choose(String serviceId);
}

public interface LoadBalancerClient extends ServiceInstanceChooser {

    // 邏輯同choose，即通過ILoadBalancer::chooseServer，然后使用返回的ServiceInstance調(diào)用下面execute方法。
    // ILoadBalancer是負載均衡策略實現(xiàn)，默認由RibbonClientConfiguration::ribbonLoadBalancer生成ZoneAwareLoadBalancer，
     T execute(String serviceId, LoadBalancerRequest request) throws IOException;

    // 根據(jù)ServiceInstance來執(zhí)行請求，調(diào)用LoadBalancerRequest::apply。
     T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest request) throws IOException;

    // 將serviceId轉(zhuǎn)換成host:port（通過注冊中心中各個服務(wù)節(jié)點的metadata）
    URI reconstructURI(ServiceInstance instance, URI original);
}

初始化流程

LoadBalancerAutoConfiguration.LoadBalancerInterceptorConfig
::ribbonInterceptor返回了一個攔截器，作用主要是在客戶端發(fā)起請求時進行攔截，進而實現(xiàn)客戶端負載均衡功能。
::restTemplateCustomizer會實例化RestTemplateCustomizer，其作用是設(shè)置::ribbonInterceptor返回的攔截器

LoadBalancerAutoConfiguration
::loadBalancedRestTemplateInitializer調(diào)用RestTemplateCustomizer::customize方法來給RestTemplate添加上LoadBalancerInterceptor攔截器。

運行時流程

public class LoadBalancerInterceptor implements ClientHttpRequestInterceptor {

    private LoadBalancerClient loadBalancer;
    private LoadBalancerRequestFactory requestFactory;

    ......
    
    public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
            final ClientHttpRequestExecution execution) throws IOException {
        final URI originalUri = request.getURI();
        String serviceName = originalUri.getHost();
        
        // 會調(diào)另一個execute方法，即LoadBalancerRequest::apply，而LoadBalancerRequest的實例是由LoadBalancerRequestFactory::createRequest生成的。
        return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
    }

}



public class LoadBalancerRequestFactory {

    ......

    public LoadBalancerRequest createRequest(final HttpRequest request,
        final byte[] body, final ClientHttpRequestExecution execution) {
    return new LoadBalancerRequest() {

        @Override
        public ClientHttpResponse apply(final ServiceInstance instance)
                throws Exception {
            // ServiceRequestWrapper重寫了getURI()，即ServiceRequestWrapper::getURI調(diào)用了LoadBalancerClient::reconstructURI
            HttpRequest serviceRequest = new ServiceRequestWrapper(request, instance, loadBalancer);
            if (transformers != null) {
                for (LoadBalancerRequestTransformer transformer : transformers) {
                    serviceRequest = transformer.transformRequest(serviceRequest, instance);
                }
            }
            
            // 這里的execution是InterceptingRequestExecution::execute，它會調(diào)用serviceRequest的HttpRequest::getURI，就是上面ServiceRequestWrapper重寫的getURI()
            return execution.execute(serviceRequest, body);
        }

    };
    }

 }