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cluster也是从rpc分出来的，包名叫com.alibaba.dubbo.rpc.cluster

也是rpc的一部分,从官方文档中可以看出

确定cluster 类型，从directory中获取注册信息，router根据规则来过滤list<Invoker> ，然后loadBalance 做负载，抽取 invoker

Directory

public interface Directory
    
      extends Node {        /**     * get service type.     *      * @return service type.     */    Class
     
       getInterface();    /**     * list invokers.     *      * @return invokers     */    List
      
       
        > list(Invocation invocation) throws RpcException;    }
       
      
     
    

Router

public interface Router extends Comparable
   
     {    /**     * get the router url.     *      * @return url     */    URL getUrl();    /**     * route.     *      * @param invokers     * @param url refer url     * @param invocation     * @return routed invokers     * @throws RpcException     */	
    
      List
     
      
       > route(List
       
        
         > invokers, URL url, Invocation invocation) throws RpcException;}
        
       
      
     
    
   

Cluster

@SPI(FailoverCluster.NAME)public interface Cluster {    /**     * Merge the directory invokers to a virtual invoker.     *      * @param 
   
         * @param directory     * @return cluster invoker     * @throws RpcException     */    @Adaptive    
    
      Invoker
     
       join(Directory
      
        directory) throws RpcException;}
      
     
    
   

LoadBalance

确定下负载算法

@SPI(RandomLoadBalance.NAME)public interface LoadBalance {	/**	 * select one invoker in list.	 * 	 * @param invokers invokers.	 * @param url refer url	 * @param invocation invocation.	 * @return selected invoker.	 */    @Adaptive("loadbalance")	
   
     Invoker
    
      select(List
     
      
       > invokers, URL url, Invocation invocation) throws RpcException;}