背景
在实时计算平台上通过YarnClient向yarn上提交flink任务时一直卡在那里，并在client端一直输出如下日志：
代码语言：javascript复制(YarnClusterDescriptor.java:1036)- Deployment took more than 60 seconds. Please check if the requested resources are available in the YARN cluster看到这个的第一反应是yarn上的资源分配问题，于是来到yarn控制台，发现Cluster Metrics中Apps Pending项为1。what?新提交的job为什么会处于pending状态了？
1. 先确定cpu和内存情况如下：
可以看出cpu和内存资源充足，没有发现问题。
2. 查看调度器的使用情况
集群中使用的调度器的类型如下图：
可以看到，集群中使用的是Capacity Scheduler调度器，也就是所谓的容量调度，这种方案更适合多租户安全地共享大型集群，以便在分配的容量限制下及时分配资源。采用队列的概念，任务提交到队列，队列可以设置资源的占比，并且支持层级队列、访问控制、用户限制、预定等等配置。但是，对于资源的分配占比调优需要更多的经验处理。但它不会出现在使用FIFO Scheduler时会出现的有大任务独占资源，会导致其他任务一直处于 pending 状态的问题。
3. 查看任务队列的情况
从上图中可以看出Configured Minimum User Limit Percent的配置为100%，由于集群目前相对较小，用户队列没有做租户划分，用的都是default队列，从图中可以看出使用的容量也只有38.2%，队列中最多可存放10000个application，而实际的远远少于10000，貎似这里也看不出来什么问题。
4. 查看resourceManager的日志
日志内容如下：
代码语言：javascript复制2020-11-26 19:33:46,669 INFO org.apache.hadoop.yarn.server.resourcemanager.ClientRMService: Allocated new applicationId: 317
2020-11-26 19:33:48,874 INFO org.apache.hadoop.yarn.server.resourcemanager.ClientRMService: Application with id 317 submitted by user root
2020-11-26 19:33:48,874 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMAppImpl: Storing application with id application_1593338489799_0317
2020-11-26 19:33:48,874 INFO org.apache.hadoop.yarn.server.resourcemanager.RMAuditLogger: USER=root IP=x.x.x.x OPERATION=Submit Application Request TARGET=ClientRMService RESULT=SUCCESS APPID=application_1593338489799_0317
2020-11-26 19:33:48,874 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMAppImpl: application_1593338489799_0317 State change from NEW to NEW_SAVING on event=START
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.recovery.RMStateStore: Storing info for app: application_1593338489799_0317
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMAppImpl: application_1593338489799_0317 State change from NEW_SAVING to SUBMITTED on event=APP_NEW_SAVED
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.ParentQueue: Application added - appId: application_1593338489799_0317 user: root leaf-queue of parent: root #applications: 16
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler: Accepted application application_1593338489799_0317 from user: root, in queue: default
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.RMAppImpl: application_1593338489799_0317 State change from SUBMITTED to ACCEPTED on event=APP_ACCEPTED
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.ApplicationMasterService: Registering app attempt : appattempt_1593338489799_0317_000001
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.rmapp.attempt.RMAppAttemptImpl: appattempt_1593338489799_0317_000001 State change from NEW to SUBMITTED
2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue: not starting application as amIfStarted exceeds amLimit
2020-11-26 19:33:48,877 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue: Application added - appId: application_1593338489799_0317 user: org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue$User@6c0d5b4d, leaf-queue: default #user-pending-applications: 1 #user-active-applications: 15 #queue-pending-applications: 1 #queue-active-applications: 15从日志中可以看到一个Application在yarn上进行资源分配的完整流程，只是这个任务因为一些原因进入了pending队列而已，与我们要查找的问题相关的日志主要是如下几行：
代码语言：javascript复制2020-11-26 19:33:48,875 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue: not starting application as amIfStarted exceeds amLimit
2020-11-26 19:33:48,877 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue: Application added - appId: application_1593338489799_0317 user: org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.LeafQueue$User@6c0d5b4d, leaf-queue: default #user-pending-applications: 1 #user-active-applications: 15 #queue-pending-applications: 1 #queue-active-applications: 15没错，问题就出来not starting application as amIfStarted exceeds amLimit，那么这个是什么原因引起的呢，我们看下stackoverflow[1]上的解释：
那么yarn.scheduler.capacity.maximum-am-resource-percent参数的真正含义是什么呢？国语意思就是集群中可用于运行application master的资源比例上限，这通常用于限制并发运行的应用程序数目，它的默认值为0.1。
查看了下集群上目前的任务总数有15个左右，每个任务分配有一个约1G左右的jobmanager（jobmanager为Application master类型的application），占15G左右，而集群上的总内存为144G，那么15>144 * 0.1 ，从而导致jobmanager的创建处于pending状态。
5. 解决验证
修改capacity-scheduler.xml的yarn.scheduler.capacity.maximum-am-resource-percent配置为如下：
代码语言：javascript复制<property>
<name>yarn.scheduler.capacity.maximum-am-resource-percent</name>
<value>0.5</value>
</property>除了动态减少队列数目外，capacity-scheduler.xml的其他配置的修改是可以动态更新的，更新命令为：
代码语言：javascript复制yarn rmadmin -refreshQueues执行命令后，在resourceManager的日志中可以看到如下输出：
代码语言：javascript复制2020-11-27 09:37:56,340 INFO org.apache.hadoop.conf.Configuration: found resource capacity-scheduler.xml at file:/work/hadoop-2.7.4/etc/hadoop/capacity-scheduler.xml
2020-11-27 09:37:56,356 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler: Re-initializing queues...
---------------------------------------------------------------------------
2020-11-27 09:37:56,371 INFO org.apache.hadoop.yarn.server.resourcemanager.scheduler.capacity.CapacityScheduler: Initialized queue mappings, override: false
2020-11-27 09:37:56,372 INFO org.apache.hadoop.yarn.server.resourcemanager.RMAuditLogger: USER=root IP=x.x.x.x OPERATION=refreshQueues TARGET=AdminServicRESULT=SUCCESS
仔细查看日志可以看到更新已经成功，在平台上重新发布任务显示成功，问题解决。
yarn Queue的配置
Resource Allocation
代码语言：javascript复制DescriptionResource Allocation using Absolute Resources configuration
CapacityScheduler supports configuration of absolute resources instead of providing Queue capacity in percentage. As mentioned in above configuration section for yarn.scheduler.capacity.<queue-path>.capacity and yarn.scheduler.capacity.<queue-path>.max-capacity, administrator could specify an absolute resource value like [memory=10240,vcores=12]. This is a valid configuration which indicates 10GB Memory and 12 VCores.
Running and Pending Application Limits
The CapacityScheduler supports the following parameters to control the running and pending applications:
Description更多配置
参考：https://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/CapacityScheduler.html
附
如果想要不重启集群来动态刷新hadoop配置可尝试如下方法：
1、刷新hdfs配置
在两个（以三节点的集群为例）namenode节点上执行：
代码语言：javascript复制hdfs dfsadmin -fs hdfs://node1:9000 -refreshSuperUserGroupsConfiguration
hdfs dfsadmin -fs hdfs://node2:9000 -refreshSuperUserGroupsConfiguration2、刷新yarn配置
在两个（以三节点的集群为例）namenode节点上执行：
代码语言：javascript复制yarn rmadmin -fs hdfs://node1:9000 -refreshSuperUserGroupsConfiguration
yarn rmadmin -fs hdfs://node2:9000 -refreshSuperUserGroupsConfiguration参考
•https://stackoverflow.com/questions/33465300/why-does-yarn-job-not-transition-to-running-state•https://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/CapacityScheduler.html•https://stackoverflow.com/questions/29917540/capacity-scheduler•https://cloud.tencent.com/developer/article/1357111•https://cloud.tencent.com/developer/article/1194501
References
[1] stackoverflow: https://stackoverflow.com/questions/33465300/why-does-yarn-job-not-transition-to-running-state
