FAQ
RPC client should deal with the IP address changes
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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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postedJul 18, '11 at 6:58p
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