[HBASE-17718] Difference between RS's servername and its ephemeral node cause SSH stop working

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.2.4, 1.1.8, 2.0.0
• Fix Version/s: 1.4.0, 2.0.0
• Hadoop Flags: Reviewed
• Release Note: Fix our accidentally registering a RegionServer's ephermal znode BEFORE we checked in with the master.
• Assignee: Allan Yang
• Reporter: Allan Yang
• Created: 02/Mar/17 07:20
• Updated: 12/Dec/18 01:55
• Resolved: 08/Mar/17 18:52

Description

After HBASE-9593, RS put up an ephemeral node in ZK before reporting for duty. But if the hosts config (/etc/hosts) is different between master and RS, RS's serverName can be different from the one stored the ephemeral zk node. The email metioned in HBASE-13753 (http://mail-archives.apache.org/mod_mbox/hbase-user/201505.mbox/%3CCANZDn9ueFEEuZMx=pZdmtLsdGLyZz=rrm1N6EQvLswYc1z-H=[e-mail]%3E) is exactly what happened in our production env.

But what the email didn't point out is that the difference between serverName in RS and zk node can cause SSH stop to work. as we can see from the code in RegionServerTracker

  @Override
  public void nodeDeleted(String path) {
    if (path.startsWith(watcher.rsZNode)) {
      String serverName = ZKUtil.getNodeName(path);
      LOG.info("RegionServer ephemeral node deleted, processing expiration [" +
        serverName + "]");
      ServerName sn = ServerName.parseServerName(serverName);
      if (!serverManager.isServerOnline(sn)) {
        LOG.warn(serverName.toString() + " is not online or isn't known to the master."+
         "The latter could be caused by a DNS misconfiguration.");
        return;
      }
      remove(sn);
      this.serverManager.expireServer(sn);
    }
  }

The server will not be processed by SSH/ServerCrashProcedure. The regions on this server will not been assigned again until master restart or failover.
I know HBASE-9593 was to fix the issue if RS report to duty and crashed before it can put up a zk node. It is a very rare case(And controllable， just fix the bug making rs to crash). But The issue I metioned can happened more often(and uncontrollable, can't be fixed in HBase, due to DNS, hosts config, etc.) and have more severe consequence.

So here I offer some solutions to discuss:
1. Revert HBASE-9593 from all branches, Andrew Purtell has reverted it in branch-0.98
2. Abort RS if master return a different name, otherwise SSH can't work properly
3. Master accepts whatever servername reported by RS and don't change it.
4.correct the zk node if master return another name( idea from Ted Yu)

Issue Links

• is broken by: HBASE-9593 Region server left in online servers list forever if it went down after registering to master and before creating ephemeral node
• relates to: HBASE-13753 HBASE-9593 made it so we register in zk with RS hostname rather than name master gave us
• links to: Review Board (branch-1)
• links to: Review Board (master)