Ming Ma created HDFS-12285:
------------------------------

             Summary: Better handling of namenode ip address change
                 Key: HDFS-12285
                 URL: https://issues.apache.org/jira/browse/HDFS-12285
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Ming Ma


RPC client layer provides functionality to detect ip address change:

{noformat}
Client.java
    private synchronized boolean updateAddress() throws IOException {
      // Do a fresh lookup with the old host name.
      InetSocketAddress currentAddr = NetUtils.createSocketAddrForHost(
                               server.getHostName(), server.getPort());
    ......
    }
{noformat}

To use this feature, we need to enable retry via 
{{dfs.client.retry.policy.enabled}}. Otherwise {{TryOnceThenFail}} RetryPolicy 
will be used; which caused {{handleConnectionFailure}} to throw 
{{ConnectException}} exception without retrying with the new ip address.

{noformat}
    private void handleConnectionFailure(int curRetries, IOException ioe
        ) throws IOException {
      closeConnection();

      final RetryAction action;
      try {
        action = connectionRetryPolicy.shouldRetry(ioe, curRetries, 0, true);
      } catch(Exception e) {
        throw e instanceof IOException? (IOException)e: new IOException(e);
      }
  ......
  }
{noformat}


However, using such configuration isn't ideal. What happens is DFSClient still 
has the cached the old ip address created by {{namenode = 
proxyInfo.getProxy();}}. Then when a new rpc connection is created, it starts 
with the old ip followed by retry with the new ip. It will be nice if DFSClient 
can refresh namenode proxy automatically.



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