[jira] [Commented] (MESOS-6090) Change master to always update registry before in-memory state

["Vinod Kone (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/MESOS-6090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15437589#comment-15437589 ] 

Vinod Kone commented on MESOS-6090:
-----------------------------------

Just so that I understand, currently

registration path:
-----------------------
added to "registering" --> registry operation --> moved to "registered"


re-registration path:
-------------------------
added to "reregistering" --> registry operation --> moved to "registered"

removal path
-----------------
added to "removing" --> registry operation --> doesn't appear in any maps (could've been moved to "removed" here instead?)

this seems easy enough to understand? can you let me know what's the discrepancy you are referring to?



> Change master to always update registry before in-memory state
> --------------------------------------------------------------
>
>                 Key: MESOS-6090
>                 URL: https://issues.apache.org/jira/browse/MESOS-6090
>             Project: Mesos
>          Issue Type: Improvement
>          Components: master
>            Reporter: Neil Conway
>            Assignee: Neil Conway
>              Labels: mesosphere
>
> When a new slave attempts to register, the registry is updated first, then the master's in-memory state is updated if the registry operation is applied successfully. However, when a slave is removed or reregisters, the master first updates its in-memory state, then updates the registry. This has two problems:
> 1. It makes it harder to reason about the correctness of concurrent operations that read in-memory state and update the registry.
> 2. It can leak incorrect information via the HTTP endpoints. That is, if we update the master's in-memory state on removal or reregistration, that change will be observable via the HTTP endpoints. If the master then fails over (and the registry operation fails), the information returned via the endpoint will be incorrect. The master has special code to avoid this inaccuracy for reconciliation (see {{Master::transitioning()}}), but not for the endpoints.
> I think it is simpler to just always update the registry first.



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