一、问题背景：
1.云主机是 Linux 环境，搭建 Hadoop 伪分布式
公网 IP：139.198.18.xxx
内网 IP：192.168.137.2
主机名：hadoop001
2.本地的core-site.xml配置如下：

<configuration>
<property>
        <name>fs.defaultFS</name>
        <value>hdfs://hadoop001:9001</value>
</property>
<property>
        <name>hadoop.tmp.dir</name>
        <value>hdfs://hadoop001:9001/hadoop/tmp</value>
</property>
</configuration>

3.本地的hdfs-site.xml配置如下：

<configuration>
<property>
       <name>dfs.replication</name>
       <value>1</value>
 </property>
</configuration>

4.云主机hosts文件配置：

[hadoop@hadoop001 ~]$ cat /etc/hosts
127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4
::1         localhost localhost.localdomain localhost6 localhost6.localdomain6

# hostname loopback address
  192.168.137.2   hadoop001

云主机将内网IP和主机名hadoop001做了映射
5.本地hosts文件配置

139.198.18.XXX     hadoop001

本地已经将公网IP和域名hadoop001做了映射
二、问题症状
1.在云主机上开启 HDFS，JPS 查看进程都没有异常，通过 Shell 操作 HDFS 文件也没有问题
2.通过浏览器访问 50070 端口管理界面也没有问题
3.在本地机器上使用 Java API 操作远程 HDFS 文件，URI 使用公网 IP，代码如下：

val uri = new URI("hdfs://hadoop001:9001")
val fs = FileSystem.get(uri,conf)
val listfiles = fs.listFiles(new Path("/data"),true)
    while (listfiles.hasNext) {
    val nextfile = listfiles.next()
    println("get file path:" + nextfile.getPath().toString())
    }
------------------------------运行结果---------------------------------
get file path:hdfs://hadoop001:9001/data/infos.txt

4.在本地机器使用SparkSQL读取hdfs上的文件并转换为DF的过程中

object SparkSQLApp {
  def main(args: Array[String]): Unit = {
  val spark = SparkSession.builder().appName("SparkSQLApp").master("local[2]").getOrCreate()
  val info = spark.sparkContext.textFile("/data/infos.txt")
  import spark.implicits._
  val infoDF = info.map(_.split(",")).map(x=>Info(x(0).toInt,x(1),x(2).toInt)).toDF()
  infoDF.show()
  spark.stop()
  }
  case class Info(id:Int,name:String,age:Int)
}

出现如下报错信息：

....
....
....
19/02/23 16:07:00 INFO Executor: Running task 0.0 in stage 0.0 (TID 0)
19/02/23 16:07:00 INFO HadoopRDD: Input split: hdfs://hadoop001:9001/data/infos.txt:0+17
19/02/23 16:07:21 WARN BlockReaderFactory: I/O error constructing remote block reader.
java.net.ConnectException: Connection timed out: no further information
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
.....
....
19/02/23 16:07:21 INFO DFSClient: Could not obtain BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 from any node: java.io.IOException: No live nodes contain block BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 after checking nodes = [DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]], ignoredNodes = null No live nodes contain current block Block locations: DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK] Dead nodes:  DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]. Will get new block locations from namenode and retry...
19/02/23 16:07:21 WARN DFSClient: DFS chooseDataNode: got # 1 IOException, will wait for 272.617680460432 msec.
19/02/23 16:07:42 WARN BlockReaderFactory: I/O error constructing remote block reader.
java.net.ConnectException: Connection timed out: no further information
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
...
...
19/02/23 16:07:42 WARN DFSClient: Failed to connect to /192.168.137.2:50010 for block, add to deadNodes and continue. java.net.ConnectException: Connection timed out: no further information
java.net.ConnectException: Connection timed out: no further information
    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:530)
    at org.apache.hadoop.hdfs.DFSClient.newConnectedPeer(DFSClient.java:3499)
...
...
19/02/23 16:08:12 WARN DFSClient: Failed to connect to /192.168.137.2:50010 for block, add to deadNodes and continue. java.net.ConnectException: Connection timed out: no further information
java.net.ConnectException: Connection timed out: no further information
    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:530)
...
...
19/02/23 16:08:12 INFO DFSClient: Could not obtain BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 from any node: java.io.IOException: No live nodes contain block BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 after checking nodes = [DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]], ignoredNodes = null No live nodes contain current block Block locations: DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK] Dead nodes:  DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]. Will get new block locations from namenode and retry...
19/02/23 16:08:12 WARN DFSClient: DFS chooseDataNode: got # 3 IOException, will wait for 11918.913311370841 msec.
19/02/23 16:08:45 WARN BlockReaderFactory: I/O error constructing remote block reader.
java.net.ConnectException: Connection timed out: no further information
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
...
...
19/02/23 16:08:45 WARN DFSClient: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt No live nodes contain current block Block locations: DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK] Dead nodes:  DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]. Throwing a BlockMissingException
19/02/23 16:08:45 WARN DFSClient: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt No live nodes contain current block Block locations: DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK] Dead nodes:  DatanodeInfoWithStorage[192.168.137.2:50010,DS-fb2e7244-165e-41a5-80fc-4bb90ae2c8cd,DISK]. Throwing a BlockMissingException
19/02/23 16:08:45 WARN DFSClient: DFS Read
org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt
    at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:1001)
...
...
19/02/23 16:08:45 WARN TaskSetManager: Lost task 0.0 in stage 0.0 (TID 0, localhost, executor driver): org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt
    at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:1001)
    at org.apache.hadoop.hdfs.DFSInputStream.blockSeekTo(DFSInputStream.java:648)
...
...
19/02/23 16:08:45 ERROR TaskSetManager: Task 0 in stage 0.0 failed 1 times; aborting job
19/02/23 16:08:45 INFO TaskSchedulerImpl: Removed TaskSet 0.0, whose tasks have all completed, from pool 
19/02/23 16:08:45 INFO TaskSchedulerImpl: Cancelling stage 0
19/02/23 16:08:45 INFO DAGScheduler: ResultStage 0 (show at SparkSQLApp.scala:30) failed in 105.618 s due to Job aborted due to stage failure: Task 0 in stage 0.0 failed 1 times, most recent failure: Lost task 0.0 in stage 0.0 (TID 0, localhost, executor driver): org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt
    at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:1001)
...
...
Caused by: org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-1358284489-192.168.137.2-1550394746448:blk_1073741840_1016 file=/data/infos.txt
    at org.apache.hadoop.hdfs.DFSInputStream.chooseDataNode(DFSInputStream.java:1001)
...
...

三、问题分析
1.本地 Shell 可以正常操作，排除集群搭建和进程没有启动的问题
2.云主机没有设置防火墙，排除防火墙没关的问题
3.云服务器防火墙开放了 DataNode 用于数据传输服务端口 默认是 50010
4.我在本地搭建了另一台虚拟机，该虚拟机和本地在同一局域网，本地可以正常操作该虚拟机的hdfs，基本确定了是由于内外网的原因。
5.查阅资料发现 HDFS 中的文件夹和文件名都是存放在 NameNode 上，操作不需要和 DataNode 通信，因此可以正常创建文件夹和创建文件说明本地和远程 NameNode 通信没有问题。那么很可能是本地和远程 DataNode 通信有问题
四、问题猜想
由于本地测试和云主机不在一个局域网，hadoop配置文件是以内网ip作为机器间通信的ip。在这种情况下,我们能够访问到namenode机器，namenode会给我们数据所在机器的ip地址供我们访问数据传输服务，但是当写数据的时候，NameNode 和DataNode 是通过内网通信的，返回的是datanode内网的ip,我们无法根据该IP访问datanode服务器。
我们来看一下其中一部分报错信息：

19/02/23 16:07:21 WARN BlockReaderFactory: I/O error constructing remote block reader.
java.net.ConnectException: Connection timed out: no further information
...
19/02/23 16:07:42 WARN DFSClient: Failed to connect to /192.168.137.2:50010 for block, add to deadNodes and continue....

从报错信息中可以看出，连接不到192.168.137.2:50010，也就是datanode的地址，因为外网必须访问“139.198.18.XXX:50010”才能访问到datanode。
为了能够让开发机器访问到hdfs，我们可以通过域名访问hdfs，让namenode返回给我们datanode的域名。
五、问题解决
1.尝试一：
在开发机器的hosts文件中配置datanode对应的外网ip和域名（上文已经配置），并且在与hdfs交互的程序中添加如下代码:

val conf = new Configuration()
conf.set("dfs.client.use.datanode.hostname", "true")

报错依旧
2.尝试二：

val spark = SparkSession
      .builder()
      .appName("SparkSQLApp")
       .master("local[2]")
      .config("dfs.client.use.datanode.hostname", "true")
      .getOrCreate()

报错依旧
3.尝试三：
在hdfs-site.xml中添加如下配置：

 <property>
        <name>dfs.client.use.datanode.hostname</name>
        <value>true</value>
    </property>

运行成功
通过查阅资料，建议在hdfs-site.xml中增加dfs.datanode.
use.datanode.hostname属性，表示datanode之间的通信也通过域名方式

<property>
        <name>dfs.datanode.use.datanode.hostname</name>
        <value>true</value>
    </property>

这样能够使得更换内网IP变得十分简单、方便，而且可以让特定datanode间的数据交换变得更容易。但与此同时也存在一个副作用，当DNS解析失败时会导致整个Hadoop不能正常工作，所以要保证DNS的可靠

总结：将默认的通过IP访问，改为通过域名方式访问。

六、参考资料
https://blog.csdn.net/vaf714/article/details/82996860
https://www.cnblogs.com/krcys/p/9146329.html
https://blog.csdn.net/dominic_tiger/article/details/71773656
https://rainerpeter.wordpress.com/2014/02/12/connect-to-hdfs-running-in-ec2-using-public-ip-addresses/