Ribbon负载均衡之原理

    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

RestTemplate对象加上LoadBalanced注解就是作了个标记，标记着RestTemplate对象发起的Http请求要被拦截和处理

LoadBalancerInterceptor对象来完成拦截的动作，查看其源码

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) {
        this(loadBalancer, new LoadBalancerRequestFactory(loadBalancer));
    }

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

查看ClientHttpRequestInterceptor接口

ClientHttpRequestInterceptor作用就是拦截客户端 HTTP 请求

LoadBalancerInterceptor实现了ClientHttpRequestInterceptor接口中intercept方法，说明LoadBalancerInterceptor可以完成拦截客户端 HTTP 请求

在intercept方法中添加断点，Debug查看

进入execute

通过Ribbon完成从eureka拉取服务信息

根据服务名获取DynamicServerListLoadBalancer对象，DynamicServerListLoadBalancer对象包含Rule和服务信息

进入getServer方法，获取服务

进入chooseServer方法，选择一个服务

根据rule（规则）选择服务，其默认规则为：ZoneAvoidanceRule

最终结果：

Ribbon负载均衡整体流程：

Ribbon负载均衡具体流程：