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https://issues.apache.org/jira/browse/HADOOP-7472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13069562#comment-13069562
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Kihwal Lee commented on HADOOP-7472:
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My current approach is to check for an address change on connection failures
and response timeouts. If a change is detected, the callers who are waiting on
the server will get an exception. I am focusing on the DFS side for now, since
it has the highest impact. Other users of RPC Client will get an exception, but
I am not looking at adding recovery mechanisms there at this time. The
important ones are for talking to NN and for others it usually make more sense
to fail early.
Again, this is not for the service level HA. Callers will see failures and they
need to have a retry logic to recover. But they won't be stuck forever anymore.
I will post a patch soon, once I do more testing. Any suggestions on how it
can be tested and what kind of test be added? I cannot think of any meaningful
test that can be added with the patch.
> 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
>
> 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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