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From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-18226) Disable reverse DNS lookup at HMaster and use default hostname provided by RegionServer
Date Mon, 19 Jun 2017 18:55:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-18226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16054584#comment-16054584
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Josh Elser commented on HBASE-18226:
------------------------------------

bq. hbase.regionserver.hostname.reported.to.master does not make sense to me honestly. Maybe
name this hbase.regionserver.hostname.disable.reversedns or something like it. 

I'm glad this is getting discussed :) I don't feel like disable.reversedns is right either
-- rDNS is still happening on the RS. I'm trying to wrap my head around what the user-facing
change is...

Nothing is really changing on the RS side (RS still computes its hostname in the same manner),
we're just "telling" the Master to not validate the reported hostname, right? It's difficult
to follow but is nice that it doesn't require any RPC changes :). I could have gotten this
wrong though.

I'm still kind of confused how this would actually work on Azure. The RS is still sending
a hostname to the Master; isn't this patch just delaying the Master from failing some RPC
to a RS? Again, I might just be missing something.

> Disable reverse DNS lookup at HMaster and use default hostname provided by RegionServer
> ---------------------------------------------------------------------------------------
>
>                 Key: HBASE-18226
>                 URL: https://issues.apache.org/jira/browse/HBASE-18226
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Duo Xu
>         Attachments: HBASE-18226.001.patch, HBASE-18226.002.patch, HBASE-18226.003.patch,
HBASE-18226.004.patch
>
>
> Description updated:
> In some unusual network environment, forward DNS lookup is supported while reverse DNS
lookup may not work properly.
> This JIRA is to address that HMaster uses the hostname passed from RS instead of doing
reverse DNS lookup to tells RS which hostname to use during reportForDuty() . This has already
been implemented by HBASE-12954 by adding "useThisHostnameInstead" field in RegionServerStatusProtos.
> Currently "useThisHostnameInstead" is optional and RS by default only passes port, server
start code and server current time info to HMaster during RS reportForDuty(). In order to
use this field, users currently need to specify "hbase.regionserver.hostname" on every regionserver
node's hbase-site.xml. This causes some trouble in
> 1. some deployments managed by some management tools like Ambari, which maintains the
same copy of hbase-site.xml across all the nodes.
> 2. HBASE-12954 is targeting multihomed hosts, which users want to manually set the hostname
value for each node. In the other cases (not multihomed), I just want RS to use the hostname
return by the node and set it in useThisHostnameInstead and pass to HMaster during reportForDuty().
> I would like to introduce a setting that if the setting is set to true, "useThisHostnameInstead"
will be set to the hostname RS gets from the node. Then HMaster will skip reverse DNS lookup
because it sees "useThisHostnameInstead" field is set in the request.
> "hbase.regionserver.hostname.reported.to.master", is it a good name?
> --------------------
> Regarding the hostname returned by the RS node, I read the source code again (including
hadoop-common dns.java). By default RS gets hostname by calling InetAddress.getLocalHost().getCanonicalHostName().
If users specify "hbase.regionserver.dns.interface" or "hbase.regionserver.dns.nameserver"
or some underlying system configuration changes (eg. modifying /etc/nsswitch.conf), it may
first read from DNS or other sources instead of first checking /etc/hosts file.



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