[jira] [Created] (HDFS-15250) Setting `dfs.client.use.datanode.hostname` to true can crash the system because of unhandled UnresolvedAddressException

["Ctest (Jira)" <ji...@apache.org>]

Ctest created HDFS-15250:
----------------------------

             Summary: Setting `dfs.client.use.datanode.hostname` to true can crash the system because of unhandled UnresolvedAddressException
                 Key: HDFS-15250
                 URL: https://issues.apache.org/jira/browse/HDFS-15250
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Ctest


*Problem:*

`dfs.client.use.datanode.hostname` by default is set to false, which means the client will use the IP address of the datanode to connect to the datanode, rather than the hostname of the datanode.

In `org.apache.hadoop.hdfs.client.impl.BlockReaderFactory.nextTcpPeer`:

 
{code:java}
 try {
   Peer peer = remotePeerFactory.newConnectedPeer(inetSocketAddress, token,
       datanode);
   LOG.trace("nextTcpPeer: created newConnectedPeer {}", peer);
   return new BlockReaderPeer(peer, false);
 } catch (IOException e) {
   LOG.trace("nextTcpPeer: failed to create newConnectedPeer connected to"
       + "{}", datanode);
   throw e;
 }
{code}
 

If `dfs.client.use.datanode.hostname` is false, then it will try to connect via IP address. If the IP address is illegal and the connection fails, IOException will be thrown from `newConnectedPeer` and be handled.

If `dfs.client.use.datanode.hostname` is true, then it will try to connect via hostname. If the hostname cannot be resolved, UnresolvedAddressException will be thrown from `newConnectedPeer`. However, UnresolvedAddressException is not a subclass of IOException so `nextTcpPeer` doesn’t handle this exception at all. This unhandled exception could crash the system.

 

*Solution:*

Since the method is handling the illegal IP address, then the illegal hostname should be also handled as well. One solution is to add the handling logic in `nextTcpPeer`:
{code:java}
 } catch (IOException e) {
   LOG.trace("nextTcpPeer: failed to create newConnectedPeer connected to"
       + "{}", datanode);
   throw e;
 } catch (UnresolvedAddressException e) {
   ... // handling logic 
 }{code}
I am very happy to provide a patch to do this.



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