Hadoop RPC 源码领略

In distributed computing, a remote procedure call ( RPC ) is when a computer program causes a procedure (subroutine) to execute in a different address space (commonly on another computer on a shared network), which is coded as if it were a normal (local) procedure call, without the programmer explicitly coding the details for the remote interaction. That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. This is a form of client–server interaction (caller is client, executor is server), typically implemented via a request–response message-passing system.

为什么要有 RPC？

地域性

当主机不可达时，通过远程调用可以使得终端操作目标机器成为可能

含糖性

底层的网络通信细节封装入 API，方便网络分布式系统的开发

模块化

在 Hadoop 分布式系统中，上层的分布式子系统（MapReduce、YARN、HDFS …）能够共用这个网络通信模块

Hadoop 的 RPC 调用链

这里我们以 “从 HDFS 下载一个文件” 为例

启动 Hadoop 集群的 DFS、YARN

可以使用 Explorer 的 50070 端口，查看 NameNode