Hortonworks沙箱环境在一个docker中设置，而Nifi在另一个容器中运行。尝试将文件从本地放入hdfs（使用GETFILE处理器从本地获取文件，并使用PUTHDFS将文件放入hdfs）会导致以下错误：
2018-06-20 15:18:07,610 ERROR [Timer-Driven Process Thread-7] o.apache.nifi.processors.hadoop.PutHDFS PutHDFS[id=1d79fc5f-0164-1000-78d8-3ac41d32affd] Failed to write to HDFS due to java.io.IOException: /lake could not be created: {}
java.io.IOException: /lake could not be created
at org.apache.nifi.processors.hadoop.PutHDFS$1.run(PutHDFS.java:259)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:360)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1678)
at org.apache.nifi.processors.hadoop.PutHDFS.onTrigger(PutHDFS.java:222)
at org.apache.nifi.processor.AbstractProcessor.onTrigger(AbstractProcessor.java:27)
at org.apache.nifi.controller.StandardProcessorNode.onTrigger(StandardProcessorNode.java:1124)
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:147)
at org.apache.nifi.controller.tasks.ContinuallyRunProcessorTask.call(ContinuallyRunProcessorTask.java:47)
at org.apache.nifi.controller.scheduling.TimerDrivenSchedulingAgent$1.run(TimerDrivenSchedulingAgent.java:128)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
此错误的原因是什么？