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From "Steve Loughran (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 Mon, 23 Jun 2008 13:24:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3426?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12607222#action_12607222

Steve Loughran commented on HADOOP-3426:

@work, on a well managed machine with a real IP address in the 0x10, subnet (but unreachable
from the outside world)
Testcase: testRDNS took 0.296 sec
	Caused an ERROR
DNS name not found [response code 3]
javax.naming.NameNotFoundException: DNS name not found [response code 3]; remaining name ''
	at com.sun.jndi.dns.DnsClient.checkResponseCode(DnsClient.java:596)
	at com.sun.jndi.dns.DnsClient.isMatchResponse(DnsClient.java:553)
	at com.sun.jndi.dns.DnsClient.doUdpQuery(DnsClient.java:399)
	at com.sun.jndi.dns.DnsClient.query(DnsClient.java:186)
	at com.sun.jndi.dns.Resolver.query(Resolver.java:64)
	at com.sun.jndi.dns.DnsContext.c_getAttributes(DnsContext.java:413)
	at com.sun.jndi.toolkit.ctx.ComponentDirContext.p_getAttributes(ComponentDirContext.java:213)
	at com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.getAttributes(PartialCompositeDirContext.java:121)
	at com.sun.jndi.toolkit.url.GenericURLDirContext.getAttributes(GenericURLDirContext.java:85)
	at javax.naming.directory.InitialDirContext.getAttributes(InitialDirContext.java:123)
	at org.apache.hadoop.net.DNS.reverseDns(DNS.java:67)
	at org.apache.hadoop.net.TestDNS.testRDNS(TestDNS.java:91)

This box does have a proper IPAddr, as resolvable from people.apache.org

> nslookup morzine.hpl.hp.com

Non-authoritative answer:
Name:   morzine.hpl.hp.com

but not reverse resolvable, their or elsewhere
> nslookup

Non-authoritative answer:
*** Can't find No answer

1. why isnt the full IP address being picked up here? A regression?
2. any code that relies on rDNS to work reliably is in trouble.

> 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: 0.16.3, 0.18.0
>         Environment: Ubuntu 8.04, at home, no reverse DNS
>            Reporter: Steve Loughran
>            Priority: Minor
>         Attachments: dns-fixes.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
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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