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From "Carsten Ziegeler (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SLING-7830) Defined leader switch
Date Mon, 20 Aug 2018 11:54:00 GMT

    [ https://issues.apache.org/jira/browse/SLING-7830?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16585833#comment-16585833
] 

Carsten Ziegeler commented on SLING-7830:
-----------------------------------------

Right, my initial idea was that the prefix is the version of the software deployed to an instance
- but that only works as long as the newly deployed version is higher as the previous one.
But you might also want to downgrade. So I would assume that we just use an increasing counter
- which is compared as a number (instead of string) and the highest has preference. Its then
up to the deployer to correctly increase the counter and keep track of it. 

> Defined leader switch
> ---------------------
>
>                 Key: SLING-7830
>                 URL: https://issues.apache.org/jira/browse/SLING-7830
>             Project: Sling
>          Issue Type: Improvement
>          Components: Discovery
>            Reporter: Carsten Ziegeler
>            Priority: Major
>
> The current leader selection is based on startup time and sling id (mainly) and is stable
across changed in the topology for as long as the leader is up and running.
> However there are use cases like blue green deployment where new instances with a new
version are started and taking over the functionality. However with the current discovery
setup, the leader would still be one of the instances with the old version.
> With a new deployed version, tasks currently bound to the leader should run on the new
version.
> Therefore the leader needs to switch and stay the leader (until it dies).
> We probably need an additional criteria for the leader selection
> /cc [~egli]



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