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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