[jira] [Commented] (FLINK-26522) Refactoring code for multiple component leader election

["Weijie Guo (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/FLINK-26522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17712881#comment-17712881 ] 

Weijie Guo commented on FLINK-26522:
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It seems that the work of FLIP-285 is being tracked in this ticket? If so, do we need to add the corresponding FLIP number to the title of this ticket?

> Refactoring code for multiple component leader election
> -------------------------------------------------------
>
>                 Key: FLINK-26522
>                 URL: https://issues.apache.org/jira/browse/FLINK-26522
>             Project: Flink
>          Issue Type: Improvement
>          Components: Runtime / Coordination
>    Affects Versions: 1.16.0
>            Reporter: Niklas Semmler
>            Assignee: Matthias Pohl
>            Priority: Major
>              Labels: pull-request-available
>         Attachments: leaderelection-FLINK-26522.class.svg, leaderelection-FLINK-26522.class.v2.svg, leaderelection-flink-1.15+.class.svg, leaderelection-flink-1.15-.class.svg
>
>
> The current implementation of the multiple component leader election faces a number of issues. These issues mostly stem from an attempt to make the multiple leader election process work just the same way as the single component leader election.
> An attempt at listing the issues follows:
> * *Naming* MultipleComponentLeaderElectionService appears by name similar to the LeaderElectionService, but is in fact closer to the LeaderElectionDriver.
> * *Similarity* The interfaces LeaderElectionService, LeaderElectionDriver and MultipleComponentLeaderElectionDriver are very similar to each other.
> * *Cyclic dependency* DefaultMultipleComponentLeaderElectionService holds a reference to the ZooKeeperMultipleComponentLeaderElectionDriver (MultipleComponentLeaderElectionDriver), which in turn holds a reference to the DefaultMultipleComponentLeaderElectionService (LeaderLatchListener)
> * *Unclear contract* With single component leader election drivers such as ZooKeeperLeaderElectionDriver a call to the LeaderElectionService#stop from JobMasterServiceLeadershipRunner#closeAsync implies giving up the leadership of the JobMaster. With the multiple component leader election this is no longer the case. The leadership is held until the HighAvailabilityServices shutdown. This logic may be difficult to understand from the perspective of one of the components (e.g., the Dispatcher)
> * *Long call hierarchy* DefaultLeaderElectionService->MultipleComponentLeaderElectionDriverAdapter->MultipleComponentLeaderElectionService->ZooKeeperMultipleComponentLeaderElectionDriver
> * *Long prefix* "MultipleComponentLeaderElection" is quite a long prefix but shared by many classes.
> * *Adapter as primary implementation* All non-testing non-multiple-component leadership drivers are deprecated. The primary implementation of LeaderElectionDriver is the adapter MultipleComponentLeaderElectionDriverAdapter.
> * *Possible redundancy* We currently have similar methods for the Dispatcher, ResourceManager, JobMaster and WebMonitorEndpoint. (E.g., for granting leadership.) As these methods are called at the same time due to the multiple component leader election, it may make sense to combine this logic into a single object.



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