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From Chris Nauroth <cnaur...@hortonworks.com>
Subject Re: Is zkfc (zookeeper failover controller) a Hadoop-only thing or something more general to Zookeeper?
Date Thu, 30 Apr 2015 21:04:24 GMT
Hello Richard,

The "hdfs zkfc" command used as part of HDFS HA is a Hadoop-specific
solution that implements an additional layer of logic on top of a
ZooKeeper distributed lock.  The additional logic relates to transitioning
NameNode processes between active and standby state, and fencing of an old
active NameNode in case it still believes itself to be active due to a
network partition or other malfunction.  The code for this resides in the
Hadoop project, not ZooKeeper.  It is considered a private implementation
detail of Hadoop, not a stable public API, so I recommend against writing
code that relies on those classes.  It might still be interesting to read
the code as inspiration for your own implementation though.  If you're
interested, take a look at the following spots in the Hadoop source tree:

hadoop-hdfs-project/hadoop-hdfs/src/main/java//org/apache/hadoop/hdfs/tools
/DFSZKFailoverController.java
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server
/namenode/ha/
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/ha/




I hope this helps.  If you have any follow up questions, I recommend
contacting user@hadoop.apache.org.

--Chris Nauroth




On 4/30/15, 1:33 PM, "Richard Sharpe" <realrichardsharpe@gmail.com> wrote:

>Hi folks,
>
>I have a need for failover in a Zookeeper cluster ... does zkfc do
>that generally or is it a Hadoop only thing?
>
>-- 
>Regards,
>Richard Sharpe
>(何以解憂?唯有杜康。--曹操)


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