ha模式下，hdfs 到hdfs报错

```
java.io.IOException: Couldn't create proxy provider class org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider
at org.apache.hadoop.hdfs.NameNodeProxies.createFailoverProxyProvider(NameNodeProxies.java:516)
at org.apache.hadoop.hdfs.NameNodeProxies.createProxy(NameNodeProxies.java:170)
at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:690)
at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:631)
at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:160)
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:2795)
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:99)
at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:2829)
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2811)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:390)
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:179)
at com.alibaba.datax.plugin.reader.hdfsreader.DFSUtil.getInputStream(DFSUtil.java:267)
at com.alibaba.datax.plugin.reader.hdfsreader.HdfsReader$Task.startRead(HdfsReader.java:354)
at com.alibaba.datax.core.taskgroup.runner.ReaderRunner.run(ReaderRunner.java:62)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.apache.hadoop.hdfs.NameNodeProxies.createFailoverProxyProvider(NameNodeProxies.java:499)
... 14 more
Caused by: java.lang.IllegalArgumentException: Interface class %s is not a valid NameNode protocol!
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
at org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider.(ConfiguredFailoverProxyProvider.java:91)
at org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider.(ConfiguredFailoverProxyProvider.java:84)
... 19 more

at com.alibaba.datax.common.exception.DataXException.asDataXException(DataXException.java:33) ~[datax-common-0.0.1-SNAPSHOT.jar:na]
at com.alibaba.datax.plugin.reader.hdfsreader.DFSUtil.getInputStream(DFSUtil.java:274) ~[hdfsreader-0.0.1-SNAPSHOT.jar:na]
at com.alibaba.datax.plugin.reader.hdfsreader.HdfsReader$Task.startRead(HdfsReader.java:354) ~[hdfsreader-0.0.1-SNAPSHOT.jar:na]
at com.alibaba.datax.core.taskgroup.runner.ReaderRunner.run(ReaderRunner.java:62) ~[datax-core-0.0.1-SNAPSHOT.jar:na]
at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]
Caused by: java.io.IOException: Couldn't create proxy provider class org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider
at org.apache.hadoop.hdfs.NameNodeProxies.createFailoverProxyProvider(NameNodeProxies.java:516) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.hdfs.NameNodeProxies.createProxy(NameNodeProxies.java:170) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:690) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.hdfs.DFSClient.(DFSClient.java:631) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.hdfs.DistributedFileSystem.initialize(DistributedFileSystem.java:160) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem.createFileSystem(FileSystem.java:2795) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem.access$200(FileSystem.java:99) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem$Cache.getInternal(FileSystem.java:2829) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem$Cache.get(FileSystem.java:2811) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:390) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.fs.FileSystem.get(FileSystem.java:179) ~[hadoop-common-2.7.3.2.6.0.3-8.jar:na]
at com.alibaba.datax.plugin.reader.hdfsreader.DFSUtil.getInputStream(DFSUtil.java:267) ~[hdfsreader-0.0.1-SNAPSHOT.jar:na]
... 3 common frames omitted
Caused by: java.lang.reflect.InvocationTargetException: null
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_144]
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_144]
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_144]
at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_144]
at org.apache.hadoop.hdfs.NameNodeProxies.createFailoverProxyProvider(NameNodeProxies.java:499) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
... 14 common frames omitted
Caused by: java.lang.IllegalArgumentException: Interface class %s is not a valid NameNode protocol!
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88) ~[guava-11.0.2.jar:na]
at org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider.(ConfiguredFailoverProxyProvider.java:91) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
at org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider.(ConfiguredFailoverProxyProvider.java:84) ~[hadoop-hdfs-2.7.3.2.6.0.3-8.jar:na]
... 19 common frames omitted
```

Start at com.alibaba.datax.plugin.reader.hdfsreader.DFSUtil.getInputStream and HdfsReader$Task.startRead, then trace the Hadoop NameNodeProxies and ConfiguredFailoverProxyProvider calls shown in the stack trace. Reproduce the HA HDFS-to-HDFS read and identify the required configuration or compatibility condition; done means the reader initializes and reads successfully without the proxy-provider exception.

Written by the indexing model from the issue text.