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https://issues.apache.org/jira/browse/HDFS-2354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13109729#comment-13109729
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Justin Joseph commented on HDFS-2354:
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Suresh, whatever you told is true when you use Linux HA for determining Active
/ Standby roles. Linux HA can easily work with scripts. Going one step further,
one can configure standByToActive script in HA framework & avoid the usage of
HAServiceProtocol interface itself.
I mean to say there are many ways of plumbing a Leader Election Service with
Namenode. We need to consider other Leader Election mechanisms also. An
alternative is Zookeeper based Leader Election Service where the LES and
Namenode may run together in the same JVM.
So the argument boils down to the question whether FailoverController daemon
should be separate from the Namenode. If they are kept separately, having only
the transition related APIs in HAServiceProtocol looks to be better decision.
But when considering the case that both FailoverController daemon & Namenode
runs in the same JVM, it is very much required that start*() & stop() APIs be
supported in the HAServiceProtocol interface
> Generalize the HAServiceProtocol interface
> ------------------------------------------
>
> Key: HDFS-2354
> URL: https://issues.apache.org/jira/browse/HDFS-2354
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: name-node
> Reporter: Justin Joseph
> Assignee: Justin Joseph
>
> This JIRA intends to revisit the patches committed for HADOOP-7455 and
> HDFS-1974 & to provide more generic interfaces which allows alternative HA
> implementations to co-exist complying with HAServiceProtocol.
> Some of the considerations are
> 1) Support life cycle methods (start*() and stop() APIs) in HAServiceProtocol
> 2) Support custom states in HAServiceProtocol
> 3) As per the patch submitted for HDFS-1974, Namenode implements HAService
> interface. This needs to be reconsidered.
> I will elaborate on these points, in the form of comments below.
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