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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7472) RPC client should deal with the IP address changes
Date Thu, 28 Jul 2011 21:32:10 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13072542#comment-13072542
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Kihwal Lee commented on HADOOP-7472:
------------------------------------

InetSocketAddress.createUnresolved() will be used (in netutils) to replace regular instantiation
of InetSocketAddress by upper layer callers. This InetSocketAddress object will stay unresolved
and the hostname field will contain the string passed to it during instantiation, whether
it's IP address or hostname.  

For making bare connections to the new namenode, this is not necessary, but for the token
cache to work, the original string used for creating the InetSocketAddress is needed. My patch
(yet to be posted) alone will work if the security is disabled. After MAPREDUCE-1824, my patch
will be very simple, much like what you initially suggested. 

> RPC client should deal with the IP address changes
> --------------------------------------------------
>
>                 Key: HADOOP-7472
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7472
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: ipc
>    Affects Versions: 0.20.205.0
>            Reporter: Kihwal Lee
>            Assignee: Kihwal Lee
>            Priority: Minor
>             Fix For: 0.20.205.0
>
>         Attachments: addr_change_dfs-1.patch.txt, addr_change_dfs.patch.txt
>
>
> The current RPC client implementation and the client-side callers assume that the hostname-address
mappings of servers never change. The resolved address is stored in an immutable InetSocketAddress
object above/outside RPC, and the reconnect logic in the RPC Connection implementation also
trusts the resolved address that was passed down.
> If the NN suffers a failure that requires migration, it may be started on a different
node with a different IP address. In this case, even if the name-address mapping is updated
in DNS, the cluster is stuck trying old address until the whole cluster is restarted.
> The RPC client-side should detect this situation and exit or try to recover.
> Updating ConnectionId within the Client implementation may get the system work for the
moment, there always is a risk of the cached address:port become connectable again unintentionally.
The real solution will be notifying upper layer of the address change so that they can re-resolve
and retry or re-architecture the system as discussed in HDFS-34. 
> For 0.20 lines, some type of compromise may be acceptable. For example, raise a custom
exception for some well-defined high-impact upper layer to do re-resolve/retry, while other
will have to restart.  For TRUNK, the HA work will most likely determine what needs to be
done.  So this Jira won't cover the solutions for TRUNK.

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