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https://issues.apache.org/jira/browse/MESOS-1696?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14154012#comment-14154012
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Benjamin Mahler commented on MESOS-1696:
----------------------------------------
https://reviews.apache.org/r/26202/
https://reviews.apache.org/r/26206/
https://reviews.apache.org/r/26207/
https://reviews.apache.org/r/26208/
> Improve reconciliation between master and slave.
> ------------------------------------------------
>
> Key: MESOS-1696
> URL: https://issues.apache.org/jira/browse/MESOS-1696
> Project: Mesos
> Issue Type: Bug
> Components: master, slave
> Reporter: Benjamin Mahler
> Assignee: Benjamin Mahler
>
> As we update the Master to keep tasks in memory until they are both terminal
> and acknowledged (MESOS-1410), the lifetime of tasks in Mesos will look as
> follows:
> {code}
> Master Slave
> {} {}
> {Tn} {} // Master receives Task T, non-terminal. Forwards to
> slave.
> {Tn} {Tn} // Slave receives Task T, non-terminal.
> {Tn} {Tt} // Task becomes terminal on slave. Update forwarded.
> {Tt} {Tt} // Master receives update, forwards to framework.
> {} {Tt} // Master receives ack, forwards to slave.
> {} {} // Slave receives ack.
> {code}
> In the current form of reconciliation, the slave sends to the master all
> tasks that are not both terminal and acknowledged. At any point in the above
> lifecycle, the slave's re-registration message can reach the master.
> Note the following properties:
> *(1)* The master may have a non-terminal task, not present in the slave's
> re-registration message.
> *(2)* The master may have a non-terminal task, present in the slave's
> re-registration message but in a different state.
> *(3)* The slave's re-registration message may contain a terminal
> unacknowledged task unknown to the master.
> In the current master / slave
> [reconciliation|https://github.com/apache/mesos/blob/0.19.1/src/master/master.cpp#L3146]
> code, the master assumes that case (1) is because a launch task message was
> dropped, and it sends TASK_LOST. We've seen above that (1) can happen even
> when the task reaches the slave correctly, so this can lead to inconsistency!
> After chatting with [~vinodkone], we're considering updating the
> reconciliation to occur as follows:
> → Slave sends all tasks that are not both terminal and acknowledged, during
> re-registration. This is the same as before.
> → If the master sees tasks that are missing in the slave, the master sends
> the tasks that need to be reconciled to the slave for the tasks. This can be
> piggy-backed on the re-registration message.
> → The slave will send TASK_LOST if the task is not known to it. Preferably in
> a retried manner, unless we update socket closure on the slave to force a
> re-registration.
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