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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3150) Add option for clients to contact DNs via hostname
Date Mon, 13 Aug 2012 23:23:38 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13433724#comment-13433724
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Aaron T. Myers commented on HDFS-3150:
--------------------------------------

The trunk patch looks pretty good to me. One little comment:

bq. @param useHostname if "name" should use a hostname or IP

This comment reads a little funny. Maybe "true to use the hostname of the DN, false to use
the IP address."

+1 once this is addressed.
                
> 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,
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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