[jira] [Created] (HADOOP-20018) ZKFC exits with a NullPointerException that hides the BindException when its RPC port is in use

["Jose Luis López (Jira)" <ji...@apache.org>]

Jose Luis López created HADOOP-20018:
----------------------------------------

             Summary: ZKFC exits with a NullPointerException that hides the BindException when its RPC port is in use
                 Key: HADOOP-20018
                 URL: https://issues.apache.org/jira/browse/HADOOP-20018
             Project: Hadoop Common
          Issue Type: Bug
          Components: ha
    Affects Versions: 3.6.0
            Reporter: Jose Luis López


*Problem*: when the ZKFC cannot bind its RPC port ({{dfs.ha.zkfc.port}}, 8019 by default), for example because another ZKFC or a stale process holds it, it exits with a NullPointerException. The BindException that explains the failure is logged once, but the exit status and the final error both name the NullPointerException:
{noformat}
ERROR org.apache.hadoop.ha.ZKFailoverController: The failover controller encounters runtime error:
java.net.BindException: Problem binding to [localhost:8019] java.net.BindException: Address already in use; For more details see:  http://wiki.apache.org/hadoop/BindException
Caused by: java.net.BindException: Address already in use
ERROR org.apache.hadoop.hdfs.tools.DFSZKFailoverController: DFSZKFailOverController exiting due to earlier exception java.lang.NullPointerException: Cannot invoke "org.apache.hadoop.ha.ZKFCRpcServer.stopAndJoin()" because "this.rpcServer" is null
INFO org.apache.hadoop.util.ExitUtil: Exiting with status 1: java.lang.NullPointerException: Cannot invoke "org.apache.hadoop.ha.ZKFCRpcServer.stopAndJoin()" because "this.rpcServer" is null
{noformat}

*Cause*: in {{ZKFailoverController.doRun()}}, {{initRPC()}} throws before {{rpcServer}} is assigned (the {{ZKFCRpcServer}} constructor fails to bind), and the {{finally}} block calls {{rpcServer.stopAndJoin()}} without a null check. The NullPointerException thrown from {{finally}} replaces the BindException in flight, so {{DFSZKFailoverController}} reports and exits with the NullPointerException.

*To reproduce*: two namenodes of one HA nameservice on the same host without a distinct {{dfs.ha.zkfc.port}} each, then start both ZKFCs. The second one fails as above. (Any process listening on 8019 does the same.)

*Proposed fix*: in the {{finally}} block of {{doRun()}}, call {{rpcServer.stopAndJoin()}} only when {{rpcServer}} is not null (the {{healthMonitor}} next to it already has that check), so the BindException reaches the caller and the exit message. A unit test can occupy the ZKFC port with a {{ServerSocket}} before starting the controller and assert that the exception reported is the BindException.

*Related*: HADOOP-18831 reports the same unchecked {{rpcServer.stopAndJoin()}}, reached through a misconfigured {{ipc.server.handler.queue.size}}; HADOOP-18811 another way {{rpcServer}} can end up null. This issue is the operational case: a port conflict, where the hidden BindException is what an operator needs to see. The same null check fixes all three paths.

Found by an end-to-end test of an HA cluster built from trunk.



--
This message was sent by Atlassian Jira
(v8.20.10#820010)

---------------------------------------------------------------------
To unsubscribe, e-mail: common-dev-unsubscribe@hadoop.apache.org
For additional commands, e-mail: common-dev-help@hadoop.apache.org