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https://issues.apache.org/jira/browse/HDFS-15250?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17326902#comment-17326902
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Stephen O'Donnell commented on HDFS-15250:
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I am reviewing some backports and came across this one. The change here does
not seem to fix anything as a couple of people have stated. Has anyone got a
stack trace from an occurrence of this error so we can see where it fails
exactly?
> 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
> Assignee: Ctest
> Priority: Major
> Fix For: 3.2.2, 3.3.1, 3.4.0, 3.1.5
>
> Attachments: HDFS-15250-001.patch, HDFS-15250-002.patch
>
>
> *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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