ResourceManager (RM)负责跟踪集群中的资源，以及调度应用程序(例如，MapReduce作业)。在Hadoop 2.4之前，集群中只有一个ResourceManager，当其中一个宕机时，将影响整个集群。高可用性特性增加了冗余的形式，即一个主动/备用的ResourceManager对，以便可以进行故障转移。
YARN HA的架构如下图所示：
本例中，各节点的角色分配如下表所示：
| 节点 | 角色 |
|---|---|
| centos01 | ResourceManager NodeManager |
| centos02 | ResourceManager NodeManager |
| centos03 | NodeManager |
下面将逐步讲解YARN HA的配置步骤。
7.1 yarn-site.xm文件配置
（1）修改yarn-site.xm文件，加入以下内容：
点击展开内容
<!--YARN HA配置-->
<property>
<name>yarn.resourcemanager.ha.enabled</name>
<value>true</value>
</property>
<property>
<name>yarn.resourcemanager.cluster-id</name>
<value>cluster1</value>
</property>
<property>
<name>yarn.resourcemanager.ha.rm-ids</name>
<value>rm1,rm2</value>
</property>
<property>
<name>yarn.resourcemanager.hostname.rm1</name>
<value>centos01</value>
</property>
<property>
<name>yarn.resourcemanager.hostname.rm2</name>
<value>centos02</value>
</property>
<property>
<name>yarn.resourcemanager.webapp.address.rm1</name>
<value>centos01:8088</value>
</property>
<property>
<name>yarn.resourcemanager.webapp.address.rm2</name>
<value>centos02:8088</value>
</property>
<property>
<name>yarn.resourcemanager.zk-address</name>
<value>centos01:2181,centos02:2181,centos03:2181</value>
</property>
<property><!--启用RM重启的功能，默认为false-->
<name>yarn.resourcemanager.recovery.enabled</name>
<value>true</value>
</property>
<property>
<name>yarn.resourcemanager.store.class</name>
<value>org.apache.hadoop.yarn.server.resourcemanager.recovery.ZKRMStateStore</value>
</property>
（2）yarn-site.xm文件配置好后，需要将其发送到集群中其它节点。
（3）接着上一章启动好的HDFS，继续进行启动YARN。
分别在centos01、centos02节点上执行以下命令，启动ResourceManager：
[hadoop@centos01 hadoop-2.7.1]$ sbin/yarn-daemon.sh start resourcemanager
分别在centos01、centos02、centos03节点上执行以下命令，启动nodemanager：
[hadoop@centos01 hadoop-2.7.1]$ sbin/yarn-daemon.sh start nodemanager
（4）YARN启动后，查看各节点Java进程：
[hadoop@centos01 hadoop-2.7.1]$ jps
3360 QuorumPeerMain
4080 DFSZKFailoverController
4321 NodeManager
4834 Jps
3908 JournalNode
3702 DataNode
4541 ResourceManager
3582 NameNode
[hadoop@centos02 hadoop-2.7.1]$ jps
4486 Jps
3815 DFSZKFailoverController
4071 NodeManager
4359 ResourceManager
3480 NameNode
3353 QuorumPeerMain
3657 JournalNode
3563 DataNode
[hadoop@centos03 hadoop-2.7.1]$ jps
3496 JournalNode
4104 Jps
3836 NodeManager
3293 QuorumPeerMain
3390 DataNode
此时浏览器输入地址http://centos01:8088 访问活动状态的ResourceManager，查看YARN的启动状态。如下图所示。
如果访问备份ResourceManager地址：http://centos02:8088 发现自动跳转到了地址http://centos01:8088。这是因为此时活动状态的ResourceManager在centos01节点上。访问备份节点的ResourceManager会自动跳转到活动节点。
7.2 测试YARN自动故障转移
在centos01节点上执行MapReduce默认的WordCount程序，当正在执行map阶段时，新开一个SSH Shell窗口，杀掉centos01的ResourceManager进程，观察程序执行过程。执行MapReduce默认的WordCount程序的命令如下：
[hadoop@centos01 hadoop-2.7.1]$ bin/yarn jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.7.1.jar wordcount /input /output
执行结果如下：
[hadoop@centos01 hadoop-2.7.1]$ bin/yarn jar share/hadoop/mapreduce/hadoop-mapreduce-examples-2.7.1.jar wordcount /input /output
18/03/16 10:48:22 INFO input.FileInputFormat: Total input paths to process : 1
18/03/16 10:48:22 INFO mapreduce.JobSubmitter: number of splits:1
18/03/16 10:48:23 INFO mapreduce.JobSubmitter: Submitting tokens for job: job_1521168402181_0001
18/03/16 10:48:23 INFO impl.YarnClientImpl: Submitted application application_1521168402181_0001
18/03/16 10:48:23 INFO mapreduce.Job: The url to track the job: http://centos01:8088/proxy/application_1521168402181_0001/
18/03/16 10:48:23 INFO mapreduce.Job: Running job: job_1521168402181_0001
18/03/16 10:48:56 INFO mapreduce.Job: Job job_1521168402181_0001 running in uber mode : false
18/03/16 10:48:57 INFO mapreduce.Job: map 0% reduce 0%
18/03/16 10:50:21 INFO mapreduce.Job: map 100% reduce 0%
18/03/16 10:50:32 INFO mapreduce.Job: map 100% reduce 100%
18/03/16 10:50:36 INFO mapreduce.Job: Job job_1521168402181_0001 completed successfully
18/03/16 10:50:37 INFO mapreduce.Job: Counters: 49
File System Counters
FILE: Number of bytes read=1321
FILE: Number of bytes written=239335
FILE: Number of read operations=0
FILE: Number of large read operations=0
FILE: Number of write operations=0
HDFS: Number of bytes read=1094
HDFS: Number of bytes written=971
HDFS: Number of read operations=6
HDFS: Number of large read operations=0
HDFS: Number of write operations=2
Job Counters
Launched map tasks=1
Launched reduce tasks=1
Data-local map tasks=1
Total time spent by all maps in occupied slots (ms)=14130
Total time spent by all reduces in occupied slots (ms)=7851
Total time spent by all map tasks (ms)=14130
Total time spent by all reduce tasks (ms)=7851
Total vcore-seconds taken by all map tasks=14130
Total vcore-seconds taken by all reduce tasks=7851
Total megabyte-seconds taken by all map tasks=14469120
Total megabyte-seconds taken by all reduce tasks=8039424
Map-Reduce Framework
Map input records=29
Map output records=109
Map output bytes=1368
Map output materialized bytes=1321
Input split bytes=101
Combine input records=109
Combine output records=86
Reduce input groups=86
Reduce shuffle bytes=1321
Reduce input records=86
Reduce output records=86
Spilled Records=172
Shuffled Maps =1
Failed Shuffles=0
Merged Map outputs=1
GC time elapsed (ms)=188
CPU time spent (ms)=1560
Physical memory (bytes) snapshot=278478848
Virtual memory (bytes) snapshot=4195344384
Total committed heap usage (bytes)=140480512
Shuffle Errors
BAD_ID=0
CONNECTION=0
IO_ERROR=0
WRONG_LENGTH=0
WRONG_MAP=0
WRONG_REDUCE=0
File Input Format Counters
Bytes Read=993
File Output Format Counters
Bytes Written=971
从上述结果中可以看出，虽然ResourceManager进程被杀掉了，但是YARN仍然能够流畅的执行，说明自动故障转移功能生效了，ResourceManager遇到故障后，自动切换到了centos02节点上继续执行。此时浏览器访问备用ResourceManager的Web端地址http://centos02:8088发现可以成功访问了。显示任务成功执行完毕。
到此，YARN HA集群搭建完毕。