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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-985) Namenode should identify DataNodes as ip:port instead of hostname:port
Date Wed, 07 Feb 2007 15:45:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12471003

Raghu Angadi commented on HADOOP-985:

I prefer #2 as well. This could be the default behavior and if dfs.datanode.dns.interface
is specified, then we can use the ip of the specific interface (this might be required for
some special cases).

Instead of modifying RPC so that namenode sees remote ip for this case, datanode can report
the ip and hostname. Datanode can open a UDP socket to namenode and check the local ip of
the socket. I think it does not even need to send any packets. Either case, it does not need
namenode to be up or wait for namenode response. 

Datanode can resolve the ip for hostname. This won't always match 'hostname -f'.. I will check
how exactly we currently get the hostname.

> Namenode should identify DataNodes as ip:port instead of hostname:port
> ----------------------------------------------------------------------
>                 Key: HADOOP-985
>                 URL: https://issues.apache.org/jira/browse/HADOOP-985
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: dfs
>    Affects Versions: 0.11.0
>            Reporter: Raghu Angadi
>         Assigned To: Raghu Angadi
>             Fix For: 0.12.0
> Right now NameNode keeps track of DataNodes with "hostname:port". One proposal is to
keep track of datanodes with "ip:port". There are various concerns expressed regd hostnames
and ip. Please add your experiences here so that we have better idea on what we should fix
> How should be calculate datanode ip: 
>             1) Just like how we calculate hostname currently with "dfs.datanode.dns.interface"
and "dfs.datanode.dns.nameserver". So if interface specified wrong, it could report ip like which might or might not be intended.
>             2) Namenode can use the remove socket address when the datanode registers.
Not sure how easy it to get this address in RPC or if this is desirable.
>             3) Namenode could just resolve the hostname when a datanode registers. It
could print of a warning if the resolved ip and reported ip don't match.
> One advantage of using IPs is that DFSClient does not need to resolve them when it connects
to datanode. This could save few milliseconds for each block. Also, DFSClient should check
all its ips to see if a given ip is local or not.
> As far I see namenode does not resolve any DNS in normal operations since it does not
actively contact datanodes. In that sense not sure if this have any change in Namenode performance.
> Thoughts?

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