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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13775) Add a conf property to retry dns reverse lookups during datanode registration
Date Fri, 03 Aug 2018 14:55:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16568303#comment-16568303

Kihwal Lee commented on HDFS-13775:

It could be meaningless if the host is running a caching daemon (e.g. nscd) and its is doing
negative caching. 

> Add a conf property to retry dns reverse lookups during datanode registration
> -----------------------------------------------------------------------------
>                 Key: HDFS-13775
>                 URL: https://issues.apache.org/jira/browse/HDFS-13775
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: namenode
>            Reporter: Aniket Mokashi
>            Priority: Major
> During DN registration, if the ip and the hostname in the DN InetAddress are the same
(i.e. reverse name lookup falied; see [the javadoc|http://docs.oracle.com/javase/6/docs/api/java/net/InetAddress.html#getHostName%28%29]),
the DN will be disallowed to register, where the DN InetAddress was obtained from the socket.
It is a performance improvement added by HDFS-3990 to avoid unnecessary DNS resolutions.
However, in an environment where DNS lookups can be flaky this can cause datanode registration
to fail permanently.
> We propose to add a conf property to retry DNS reverse lookup during DN registration.
Otherwise, clusters with flaky reverse DNS lookup will fail permanently.

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