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https://issues.apache.org/jira/browse/HDDS-3270?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Stephen O'Donnell reassigned HDDS-3270:
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Assignee: Stephen O'Donnell
> Allow safemode listeners to be notified when some precheck rules pass
> ---------------------------------------------------------------------
>
> Key: HDDS-3270
> URL: https://issues.apache.org/jira/browse/HDDS-3270
> Project: Hadoop Distributed Data Store
> Issue Type: Improvement
> Components: SCM
> Affects Versions: 0.6.0
> Reporter: Stephen O'Donnell
> Assignee: Stephen O'Donnell
> Priority: Major
>
> As part of the SCM safemode process, there are some rules which must pass
> before safemode can be exited.
> One of these rules is the number of registered datanodes and another is that
> at least one pipeline must be created and open.
> Currently, pipeline creation is attempted each time a node registers. As soon
> as the 3rd node registers, pipelines will be created.
> There are two issue with this:
> 1. With network topology, if the first 3 nodes are all from the same rack, a
> non-rackaware pipeline will get created.
> 2. With multi-raft, it would be better if more nodes are registered to allow
> the multiple pipelines per node to be spread across all the available nodes.
> The proposal here, is to introduce a new sub-state into the safemode process,
> call "preCheckComplete". When adding rules to the Safemode Manager, some
> rules can be tagged as "preCheck" (eg number of datanodes registered). When
> all all the pre-check rules have passed a notification will be sent to all
> safemode listeners:
> {code}
> safeModeIsOn -> true
> preCheckComplete -> true
> {code}
> That will allow the listener to take action on this first stage completing.
> In the case of PipelineManager, it will then allow pipelines to be created.
> After the remaining rules have been passed, safemode will exit as normal, by
> sending a second event:
> {code}
> safeModeIsOn -> false
> preCheckComplete -> true
> {code}
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