[jira] [Created] (HDFS-3081) SshFenceByTcpPort uses netcat incorrectly

["Philip Zeyliger (Created) (JIRA)" <ji...@apache.org>]

SshFenceByTcpPort uses netcat incorrectly
-----------------------------------------

                 Key: HDFS-3081
                 URL: https://issues.apache.org/jira/browse/HDFS-3081
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: ha
    Affects Versions: 0.24.0
            Reporter: Philip Zeyliger


SshFencyByTcpPort currently assumes that the NN is listening on localhost.  Typical setups have the namenode listening just on the hostname of the namenode, which would lead "nc -z" to not catch it.

Here's an example in which the NN is running, listening on 8020, but doesn't respond to "localhost 8020".
{noformat}
[root@xxx ~]# lsof -P -p 5286 | grep -i listen
java    5286 root  110u  IPv4            1772357              TCP xxx:8020 (LISTEN)
java    5286 root  121u  IPv4            1772397              TCP xxx:50070 (LISTEN)
[root@xxx ~]# nc -z localhost 8020
[root@xxx ~]# nc -z xxx 8020
Connection to xxx 8020 port [tcp/intu-ec-svcdisc] succeeded!
{noformat}

Here's the likely offending code:
{code}
        LOG.info(
            "Indeterminate response from trying to kill service. " +
            "Verifying whether it is running using nc...");
        rc = execCommand(session, "nc -z localhost 8020");
{code}

Naively, we could rely on netcat to the correct hostname (since the NN ought to be listening on the hostname it's configured as), or just to use fuser.  Fuser catches ports independently of what IPs they're bound to:

{noformat}
[root@xxx ~]# fuser 1234/tcp
1234/tcp:             6766  6768
[root@xxx ~]# jobs
[1]-  Running                 nc -l localhost 1234 &
[2]+  Running                 nc -l rhel56-18.ent.cloudera.com 1234 &
[root@xxx ~]# sudo lsof -P | grep -i LISTEN | grep -i 1234
nc         6766      root    3u     IPv4            2563626                 TCP localhost:1234 (LISTEN)
nc         6768      root    3u     IPv4            2563671                 TCP xxx:1234 (LISTEN)
{noformat}

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