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Date: Tue, 14 Aug 2012 02:26:38 +1100 (NCT)
From: "Daryn Sharp (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-3150) Add option for clients to contact
 DNs via hostname
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    [ https://issues.apache.org/jira/browse/HDFS-3150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433209#comment-13433209 ] 

Daryn Sharp commented on HDFS-3150:
-----------------------------------

Question: should we consider tying this and the use_ip config together?  I think that if you need hosts names for multihoming you probably need host names for everything.  Does this even work if use_ip is true (default value)?
                
> Add option for clients to contact DNs via hostname
> --------------------------------------------------
>
>                 Key: HDFS-3150
>                 URL: https://issues.apache.org/jira/browse/HDFS-3150
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: data-node, hdfs client
>    Affects Versions: 1.0.0, 2.0.0-alpha
>            Reporter: Eli Collins
>            Assignee: Eli Collins
>             Fix For: 1.1.0
>
>         Attachments: hdfs-3150-b1.txt, hdfs-3150-b1.txt, hdfs-3150.txt, hdfs-3150.txt
>
>
> The DN listens on multiple IP addresses (the default {{dfs.datanode.address}} is the wildcard) however per HADOOP-6867 only the source address (IP) of the registration is given to clients. HADOOP-985 made clients access datanodes by IP primarily to avoid the latency of a DNS lookup, this had the side effect of breaking DN multihoming (the client can not route the IP exposed by the NN if the DN registers with an interface that has a cluster-private IP). To fix this let's add back the option for Datanodes to be accessed by hostname.
> This can be done by:
> # Modifying the primary field of the Datanode descriptor to be the hostname, or 
> # Modifying Client/Datanode <-> Datanode access use the hostname field instead of the IP
> Approach #2 does not require an incompatible client protocol change, and is much less invasive. It minimizes the scope of modification to just places where clients and Datanodes connect, vs changing all uses of Datanode identifiers.
> New client and Datanode configuration options are introduced:
> - {{dfs.client.use.datanode.hostname}} indicates all client to datanode connections should use the datanode hostname (as clients outside cluster may not be able to route the IP)
> - {{dfs.datanode.use.datanode.hostname}} indicates whether Datanodes should use hostnames when connecting to other Datanodes for data transfer
> If the configuration options are not used, there is no change in the current behavior.

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