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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3426) Datanode does not start up if the local machines DNS isnt working right and dfs.datanode.dns.interface==default
Date Thu, 28 Aug 2008 21:35:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626754#action_12626754
] 

Raghu Angadi commented on HADOOP-3426:
--------------------------------------


> 1. In these situations, its usually better to fall back to using "localhost" or 127.0.0.1
as a hostname if Java can't work it out for itself,

Should this be a config option that is disabled by default? What is worse than seeing an error
is not seeing an error message. Are there any alternatives (using first available id adress
etc)?

> 2. Its often good to cache this if used in lots of parts of the system, otherwise the
30s timeouts can cause problems of their own.

This part I understand.. I thought this is all that this jira did.

I still need to go through the patch but was surprised to see the changes with Ip4, Ip6 etc.


> Datanode does not start up if the local machines DNS isnt working right and dfs.datanode.dns.interface==default
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-3426
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3426
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.19.0
>         Environment: Ubuntu 8.04, at home, no reverse DNS
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Minor
>         Attachments: hadoop-3426.patch, hadoop-3426.patch
>
>
> This is the third Java project I've been involved in that doesnt work on my home network,
due to implementation issues with  java.net.InetAddress.getLocalHost(), issues that only show
up on an unamanged network. Fortunately my home network exists to find these problems early.
> In hadoop, if the local hostname doesnt resolve, the datanode does not start up:
> Caused by: java.net.UnknownHostException: k2: k2
> at java.net.InetAddress.getLocalHost(InetAddress.java:1353)
> at org.apache.hadoop.net.DNS.getDefaultHost(DNS.java:185)
> at org.apache.hadoop.dfs.DataNode.startDataNode(DataNode.java:184)
> at org.apache.hadoop.dfs.DataNode.(DataNode.java:162)
> at org.apache.hadoop.dfs.ExtDataNode.(ExtDataNode.java:55)
> at org.smartfrog.services.hadoop.components.datanode.DatanodeImpl.sfStart(DatanodeImpl.java:60)
> While this is a valid option in a production (non-virtual) cluster, if you are playing
with VMWare/Xen private networks or on a home network, you can't rely on DNS. 
> 1. In these situations, its usually better to fall back to using "localhost" or 127.0.0.1
as a hostname if Java can't work it out for itself,
> 2. Its often good to cache this if used in lots of parts of the system, otherwise the
30s timeouts can cause problems of their own.

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