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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 Fri, 29 Aug 2008 14:30:46 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12626989#action_12626989
] 

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

> OK. One thing we can't rely on here is any kind of rDNS to work, hostname lookup may
time out, etc.

Right. we need to discourage depending on rDNS unless it is really required. rDNS failure
should generally be not a fatal error.

> I was thinking a little private xen/vmware virtual cluster with no external connectivity
or DNS. Its a self-contained network.
In that case using the first available ip address works, right?

> One thing that is hard when handling different network setups is actually [...]
agreed.. we should clarify the requirements, tolerate less perfect set ups, and generally
be more end user friendly :) .

> 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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