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https://issues.apache.org/jira/browse/HDFS-13523?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16566256#comment-16566256
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Konstantin Shvachko commented on HDFS-13523:
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Agree with [~xkrogen] overriding the {{StartupOption}} is a bad idea. Just
using {{StartupOption.OBSERVER}} as the parameter for {{createNameNode()}}
should start an Observer NameNode. It does not require changes in
{{MiniDFSNNTopology}} to specify the Observer.
The main purpose of this jira is to provide methods in {{MiniDFSCluster}} to
support Observer NameNode.
# Startup. In HA setup (where we get SBNs and now Observers) NameNodes start
in Standby state, then one of them is transitioned into Active. Same with
Observer. It starts in Standby state then transitions to Obersver.
{{transitionToStandby()}} has been introduced in one of the prior jiras. You
don't need to worry about startup. See {{TestObserverNode}}.
# So more specific goal is to look at {{TestObserverNode}} and
{{TestStateAlignmentContextWithHA}} and see what common methods could be added
to {{MiniDFSCluster}} or to {{HATestUtil}}, to simplify starting and
manipulating mini clusters with observer nodes.
Examples include:
** Moving {{setObserverRead()}} into {{MiniDFSCluster}}
** Providing methods like {{setUpCluster(int numObservers)}} to setup a
cluster with given number of observers.
> Support observer nodes in MiniDFSCluster
> ----------------------------------------
>
> Key: HDFS-13523
> URL: https://issues.apache.org/jira/browse/HDFS-13523
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode, test
> Reporter: Erik Krogen
> Assignee: Sherwood Zheng
> Priority: Major
> Attachments: HADOOP-13523-HADOOP-12943.000.patch,
> HADOOP-13523-HADOOP-12943.001.patch, HDFS-13523-HDFS-12943.001.patch,
> HDFS-13523-HDFS-12943.002.patch, HDFS-13523-HDFS-12943.003.patch,
> HDFS-13523-HDFS-12943.004.patch
>
>
> MiniDFSCluster should support Observer nodes so that we can write decent
> integration tests.
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