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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 Mon, 01 Aug 2011 22:00:50 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13073815#comment-13073815
] 

Kihwal Lee commented on HADOOP-7472:
------------------------------------

The new patch is very close to what Suresh intially suggested. I decided not to do the check
at response timeout because it changes the service semantics. 

Following is the result of my testing described above.
{quote}
$ ./hadoop fs -ls
11/08/01 16:53:20 INFO ipc.Client: Retrying connect to server: testhost/127.0.0.1:9000. Already
tried 0 time(s).
11/08/01 16:53:21 INFO ipc.Client: Retrying connect to server: testhost/127.0.0.1:9000. Already
tried 1 time(s).
11/08/01 16:53:22 INFO ipc.Client: Retrying connect to server: testhost/127.0.0.1:9000. Already
tried 2 time(s).
11/08/01 16:53:23 INFO ipc.Client: Retrying connect to server: testhost/127.0.0.1:9000. Already
tried 3 time(s).
11/08/01 16:53:23 WARN ipc.Client: Address change detected. Host: testhost OldAddr: 127.0.0.1
NewAddr: testhost/10.xx.xx.xx
11/08/01 16:53:24 INFO ipc.Client: Retrying connect to server: testhost/10.xx.xx.xx:9000.
Already tried 0 time(s).
11/08/01 16:53:25 INFO ipc.Client: Retrying connect to server: testhost/10.xx.xx.xx:9000.
Already tried 1 time(s).
11/08/01 16:53:26 INFO ipc.Client: Retrying connect to server: testhost/10.xx.xx.xx:9000.
Already tried 2 time(s).
11/08/01 16:53:27 INFO ipc.Client: Retrying connect to server: testhost/10.xx.xx.xx:9000.
Already tried 3 time(s).
Found 1 items
-rw-r--r--   1 kihwal supergroup  327499776 2011-07-22 11:30 /user/kihwal/ddd
{quote}

The result of test-patch:

     [exec] -1 overall.
     [exec]
     [exec]     +1 @author.  The patch does not contain any @author tags.
     [exec]
     [exec]     -1 tests included.  The patch doesn't appear to include any new or modified
tests.
     [exec]                         Please justify why no tests are needed for this patch.
     [exec]
     [exec]     +1 javadoc.  The javadoc tool did not generate any warning messages.
     [exec]
     [exec]     +1 javac.  The applied patch does not increase the total number of javac compiler
warnings.
     [exec]
     [exec]     +1 findbugs.  The patch does not introduce any new Findbugs (version 1.3.9)
warnings.


When the patch for MAPREDUCE-1824 becomes available, there might be an overlap where connect()
is called.

> 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-2.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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