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https://issues.apache.org/jira/browse/HADOOP-7472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13069816#comment-13069816
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Kihwal Lee commented on HADOOP-7472:
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The attached patch includes changes to DFSClient and ipc.Client. The RPC
callers will get InvalidRPCAddressException when the IP address of the name
node changes. DFSClient handles this exception so that the RPC client is
recreated with the new address. Subsequent calls are directed to the new name
node.
This patch doesn't modify other RPC callers. They will get an exception and
some will recover automatically, others won't. The datanode heartbeat seems to
recover automatically. I assume the cluster will be restarted with a new config
anyway when the name node has to move.
There is no test included in this patch. I tested it by flipping system
configuration and killing/starting the namenode at the right moment and order.
I welcome any suggestion. If no one can come up with a reasonable automated
test for our existing testing framework, I will request for an exemption after
more through testing on a real cluster.
> 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
> Attachments: 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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