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https://issues.apache.org/jira/browse/HADOOP-17052?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17119393#comment-17119393
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Mingliang Liu commented on HADOOP-17052:
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[~dhegde] Thanks for reporting and providing a patch.
# The two stack trace you posted are both for read. If you have a write
pipeline stack (e.g. DataStreamer as mentioned by [~hemanthboyina]), that will
be useful here for reference.
# The idea you two have figured looks good to me. I have approved the PR. If
there is no more objections, I'll commit it in 3 days. I think it is fine and
actually better to retry on one peer in case of generic host unresolvable
problem, be it unchecked UnresolvedAddressException or checked
UnknownHostException (IOE).
# [~dhegde] It is highly recommended to make the JIRA title and PR subject the
same. You can edit either places since they both look good to me.
> NetUtils.connect() throws an exception the prevents any retries when hostname
> resolution fails
> ----------------------------------------------------------------------------------------------
>
> Key: HADOOP-17052
> URL: https://issues.apache.org/jira/browse/HADOOP-17052
> Project: Hadoop Common
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.10.0, 2.9.2, 3.2.1, 3.1.3
> Reporter: Dhiraj Hegde
> Assignee: Dhiraj Hegde
> Priority: Major
> Attachments: stack_trace2
>
>
> Hadoop components are increasingly being deployed on VMs and containers. One
> aspect of this environment is that DNS is dynamic. Hostname records get
> modified (or deleted/recreated) as a container in Kubernetes (or even VM) is
> being created/recreated. In such dynamic environments, the initial DNS
> resolution request might return resolution failure briefly as DNS client
> doesn't always get the latest records. This has been observed in Kubernetes
> in particular. In such cases NetUtils.connect() appears to throw
> java.nio.channels.UnresolvedAddressException. In much of Hadoop code (like
> DFSInputStream and DFSOutputStream), the code is designed to retry
> IOException. However, since UnresolvedAddressException is not child of
> IOException, no retry happens and the code aborts immediately. It is much
> better if NetUtils.connect() throws java.net.UnknownHostException as that is
> derived from IOException and the code will treat this as a retry-able error.
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