[
https://issues.apache.org/jira/browse/FLINK-26522?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17653998#comment-17653998
]
Matthias Pohl commented on FLINK-26522:
---------------------------------------
We might want to extend the interface a bit to harden the contract of
{{LeaderElectionService}}: {{LeaderElectionService#remove(LeaderContender)}}
requires the contender to be passed. The contract proposal defines the contract
in a way that a {{NoSuchElementException}} is thrown if the passed contender
does not match any registered one. The removal of contenders usually happens in
{{closeAsync}} calls which should be idempotent (i.e. we want to call them
multiple times without problems). Therefore, we would want to check whether the
contender was already removed to avoid running into the
{{NoSuchElementException}}. I propose adding a method {{isRegistered}} to fix
this issue.
> 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
> Priority: Major
> Labels: pull-request-available
> Attachments: leaderelection-FLINK-26522.class.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.
--
This message was sent by Atlassian Jira
(v8.20.10#820010)
