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From "Owen O'Malley (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 17:15:05 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12471031
] 

Owen O'Malley commented on HADOOP-985:
--------------------------------------

I think the best way to support rpc calls being able to find the IP address of the caller
would be to have a static method in RPC that uses a thread-local variable to return the IP
address of the caller. Clearly the RPC framework would set the variable before calling the
method on the server and clear it when it was done. Something like:

  /**
   * Get the host ip address of the caller. Only valid on the server while running the remote
procedure.
   * @return the dotted ip address of the caller or NULL if not in an RPC call
   */
  public static String getHostAddress() { ... }

> 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
etc.
> 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
127.0.0.1 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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