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https://issues.apache.org/jira/browse/HADOOP-7472?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13078937#comment-13078937
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Kihwal Lee commented on HADOOP-7472:
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If you call InetAddress.getByAddress(String hostname, byte[] addr), the
hostname is saved in the new InetAddress, so getHostName() will return the
hostname used to instantiate this InetAddress object. But if
InetAddress.getByName() is used, only the resolved address is saved. The
hostname is saved in {{h_name}} of {{struct hostent}}, but it is never looked
at.
So, {{new InetSocketAddress(name, port)}} will not store {{name}] in its
hostName field nor in InetAddress.hostname.
I need to do lookup with the old name, and then construct an InetAddress with
the old name and the new address. Only then I can create a new
InetSocketAddress with it and InetSocketAddress.getHostName() will get the name
from the InetAddress I created.
This assumes that the InetSocketAddress passed to getProxy() contains the name
or the alias that stays the same after IP address changes. My very first patch
tried to address this in DFSClient, but it was limited in scope.
MAPREDUCE-2764 will have more comprehensive solution.
> 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-3.patch.txt,
> addr_change_dfs.patch.txt, addr_change_dfs_0_20s.patch.txt,
> addr_change_dfs_trunk-1.patch.txt, addr_change_dfs_trunk.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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