Yarn-Client 模式下执行spark任务， Error initializing SparkContext. Failed to connect to driver!
redhat7.3系统
大数据集群4台机器--集群外1台机器
通过集群外的机器向大数据集群提交spark-sql任务，任务如下：
任务执行失败。
主要表现为：
服务端shell日志报错为：
ERROR SparkContext: Error initializing SparkContext.
org.apache.spark.SparkException: Yarn application has already ended! It might have been killed or unable to launch application master.
Yarn端日志报错为：
Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:52 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:53 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:54 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:55 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:56 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:57 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:57 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:28:59 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:00 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:01 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:02 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:03 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:04 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:05 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:06 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:06 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:07 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:09 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:10 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:11 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:12 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:13 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:14 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:15 ERROR ApplicationMaster: Failed to connect to driver at 10.10.98.191:33937, retrying ...
17/10/12 11:29:15 ERROR ApplicationMaster: Uncaught exception:
org.apache.spark.SparkException: Failed to connect to driver!
解决办法：
关闭集群外机器的防火墙。
防火墙的开启、关闭、禁用命令
（1）设置开机启用防火墙：systemctl enable firewalld.service
（2）设置开机禁用防火墙：systemctl disable firewalld.service
（3）启动防火墙：systemctl start firewalld
（4）关闭防火墙：systemctl stop firewalld
（5）检查防火墙状态：systemctl status firewalld
路过的坑：
一开始就查看过防火墙，但是使用的命令是iptables，没有返回信息，就误以为是防火墙已关闭，但实际上端口一直没ping通。
补充：
今天又一次出现了这个错误，防火墙也已经关闭，但是还是没解决问题，然后发现是IP地址的原因。
服务器存在管理网IP和业务网IP,而从大数据集群返回时，总是选择连接管理网IP,而大数据集群ping 管理网IP却ping不通，所以这个问题的原因有两个，一个是地址ping不通，一个是端口ping不通。
针对端口ping不通，我们的解决办法是关闭防火墙；
针对IP地址ping不通，我们的解决办法是在saprk-sql命令后面加上--conf spark.driver.host=$your_ip_address
参考文章：
https://www.cnblogs.com/fbiswt/p/4667956.html
1、客户端安装的机器一般是虚拟机，虚拟机的名称可能是随便搞的，然而，yarn-client模式提交任务，是默认把本机当成driver的。所以导致其他的机器无法通过host的name直接访问这台机器。报错就是Failed to connect to driver at x.x.x.x，retrying.....
解决办法：在命令后面加上一个--conf spark.driver.host=$your_ip_address，后面直接填客户端机器的IP地址就行。还有一个办法：export SPARK_JAVA_OPTS="-Dspark.driver.host=$your_ip_address"，但是这种方法你在用完yarn-client后就没有办法再用yarn-cluster了。千万不能把这个参数配置到spark-default.conf里面。
2、客户机的防火墙是开着的，把端口给屏蔽掉了。因为这个访问机器的端口，是随机的...所以还是关闭防火墙比较好。