目的
记录学习hadoop过程中遇到的基础问题，无关大小、无关困扰时间长短。
问题一 全分布式环境中运行mapred程序，报异常：java.net.noroutetoHostException: 没有到主机的路由
在全分布式环境中运行mapred程序，报异常：java.net.noroutetoHostException: 没有到主机的路由，但同样的配置、同样的程序，在伪分布式环境中是没有问题的。具体异常信息如下：
2019-09-14 15:37:44,018 INFO mapreduce.Job: Running job: job_1568442070466_0003 2019-09-14 15:43:46,231 INFO mapreduce.Job: Job job_1568442070466_0003 running in uber mode : false 2019-09-14 15:43:46,233 INFO mapreduce.Job: map 0% reduce 0% 2019-09-14 15:43:46,273 INFO mapreduce.Job: Job job_1568442070466_0003 Failed with state Failed due to: Application application_1568442070466_0003 Failed 2 times due to Error launching appattempt_1568442070466_0003_000002. Got exception: java.net.noroutetoHostException: No Route to Host from master/192.168.212.132 to slave1:45816 Failed on socket timeout exception: java.net.noroutetoHostException: 没有到主机的路由; For more details see: http://wiki.apache.org/hadoop/noroutetoHost at sun.reflect.GeneratedConstructorAccessor56.newInstance(UnkNown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.apache.hadoop.net.NetUtils.wrapWithMessage(NetUtils.java:831) at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:782) at org.apache.hadoop.ipc.Client.getRpcResponse(Client.java:1515) at org.apache.hadoop.ipc.Client.call(Client.java:1457) at org.apache.hadoop.ipc.Client.call(Client.java:1367) at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:228) at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:116) at com.sun.proxy.$Proxy83.startContainers(UnkNown Source) at org.apache.hadoop.yarn.api.impl.pb.client.ContainerManagementProtocolPBClientImpl.startContainers(ContainerManagementProtocolPBClientImpl.java:128) at sun.reflect.GeneratedMethodAccessor88.invoke(UnkNown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:422) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeMethod(RetryInvocationHandler.java:165) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invoke(RetryInvocationHandler.java:157) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeOnce(RetryInvocationHandler.java:95) at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:359) at com.sun.proxy.$Proxy84.startContainers(UnkNown Source) at org.apache.hadoop.yarn.server.resourcemanager.amlauncher.AMLauncher.launch(AMLauncher.java:123) at org.apache.hadoop.yarn.server.resourcemanager.amlauncher.AMLauncher.run(AMLauncher.java:308) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: java.net.noroutetoHostException: 没有到主机的路由 at sun.nio.ch.socketChannelImpl.checkConnect(Native Method) at sun.nio.ch.socketChannelImpl.finishConnect(SocketChannelImpl.java:717) at org.apache.hadoop.net.socketIOWithTimeout.connect(SocketIOWithTimeout.java:206) at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:531) at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:690) at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:794) at org.apache.hadoop.ipc.Client$Connection.access$3700(Client.java:411) at org.apache.hadoop.ipc.Client.getConnection(Client.java:1572) at org.apache.hadoop.ipc.Client.call(Client.java:1403) ... 19 more . Failing the application. 2019-09-14 15:43:46,332 INFO mapreduce.Job: Counters: 0异常信息
问题定位
1、虽然异常信息中只提到了一个slave节点，但已知所有节点配置均一模一样，所以这应该是一个共性问题；
2、根据异常的字面意思，即当前提交工作的master节点找不到slave节点，而找不到无非是以下几种情况：
- 当前主机的hosts配置错误
经ping slave1命令测试成功，这个情况可以排除。 - 目标主机对应端口（45816）未打开
打开所有slave节点的45816端口后，重新提交一次作业观察运行情况。
再次提交作业，发现仍然报错，但此时的端口变成了43910，这个端口我们并未处理，自然也是关闭的。由端口的变化，可推测，每次提交作业调度运行时，用到的IPC端口是框架随机使用的，所以再用打开某个端口的方式来解决这个问题已经明显不可取了。
解决思路有两个：1、为slave节点添加对master节点的IP级别允许通过；2、使框架用到的ipc端口固定，然后用允许端口的方式开放。（暂未找到这种配置方法）
在使用解决思路1，使用以下命令开放给master节点访问：firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.212.132" accept' firewall-cmd --reload
再次提交作业，发现作业已经可以运行起来，但仍有noroutetoHostException报错，但并不影响mapreduce程序的执行。推测是由于网络波动、或者虚拟机的局限性导致的间歇性丢失目标主机，有哪位大神知道，还望指点一二，这里先不深究了。错误信息如下：
2019-09-14 17:31:55,733 INFO mapreduce.Job: Task Id : attempt_1568452715996_0001_m_000013_2, Status : Failed Container launch Failed for container_1568452715996_0001_01_000056 : java.net.noroutetoHostException: No Route to Host from slave3/192.168.212.135 to slave1:42387 Failed on socket timeout exception: java.net.noroutetoHostException: 没有到主机的路由; For more details see: http://wiki.apache.org/hadoop/noroutetoHost at sun.reflect.GeneratedConstructorAccessor39.newInstance(UnkNown Source) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) at java.lang.reflect.Constructor.newInstance(Constructor.java:423) at org.apache.hadoop.net.NetUtils.wrapWithMessage(NetUtils.java:831) at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:782) at org.apache.hadoop.ipc.Client.getRpcResponse(Client.java:1515) at org.apache.hadoop.ipc.Client.call(Client.java:1457) at org.apache.hadoop.ipc.Client.call(Client.java:1367) at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:228) at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:116) at com.sun.proxy.$Proxy84.startContainers(UnkNown Source) at org.apache.hadoop.yarn.api.impl.pb.client.ContainerManagementProtocolPBClientImpl.startContainers(ContainerManagementProtocolPBClientImpl.java:128) at sun.reflect.GeneratedMethodAccessor12.invoke(UnkNown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:422) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeMethod(RetryInvocationHandler.java:165) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invoke(RetryInvocationHandler.java:157) at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeOnce(RetryInvocationHandler.java:95) at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:359) at com.sun.proxy.$Proxy85.startContainers(UnkNown Source) at org.apache.hadoop.mapreduce.v2.app.launcher.ContainerLauncherImpl$Container.launch(ContainerLauncherImpl.java:160) at org.apache.hadoop.mapreduce.v2.app.launcher.ContainerLauncherImpl$EventProcessor.run(ContainerLauncherImpl.java:394) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748) Caused by: java.net.noroutetoHostException: 没有到主机的路由 at sun.nio.ch.socketChannelImpl.checkConnect(Native Method) at sun.nio.ch.socketChannelImpl.finishConnect(SocketChannelImpl.java:717) at org.apache.hadoop.net.socketIOWithTimeout.connect(SocketIOWithTimeout.java:206) at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:531) at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:690) at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:794) at org.apache.hadoop.ipc.Client$Connection.access$3700(Client.java:411) at org.apache.hadoop.ipc.Client.getConnection(Client.java:1572) at org.apache.hadoop.ipc.Client.call(Client.java:1403) ... 19 more异常信息之一
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