Yarn背景

Yarn全称为Yet Another Resource Negotiator。是一种资源管理器，负责集群资源的管理和调度，它可以实现对集群所有cpu，内存，文件系统，磁盘等各种资源的分配。
yarn是hadoop mapreduce的第二版本，解决version1的一些问题。

名词解释

Application Master (AM):
Resource Manager (RM):
Node Manager (NM):

The idea is to have a global ResourceManager (RM) and per-application ApplicationMaster (AM). An application is either a single job or a DAG of jobs.
The ResourceManager and the NodeManager form the data-computation framework. The ResourceManager is the ultimate authority that arbitrates resources among all the applications in the system. The NodeManager is the per-machine framework agent who is responsible for containers, monitoring their resource usage (cpu, memory, disk, network) and reporting the same to the ResourceManager/Scheduler.
The per-application ApplicationMaster is, in effect, a framework specific library and is tasked with negotiating resources from the ResourceManager and working with the NodeManager(s) to execute and monitor the tasks.

也就是说，RM和NM组成了数据计算框架，RM管理系统中所有资源的框架，NM是管理容器的机器级别的框架（管理机器cpu内存硬盘网络资源）并汇报给RM/Scheduler。应用级别的AM是框架定义的库，负责与RM协调资源，和NM一起执行并监控task。

Scheduler是RM的两个主要部分之一，分别是Scheduler和Applications Manager (ASM)。