[jira] [Assigned] (MESOS-1696) Improve reconciliation between master and slave.

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

     [ https://issues.apache.org/jira/browse/MESOS-1696?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vinod Kone reassigned MESOS-1696:
---------------------------------

    Assignee: Vinod Kone

> 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: Vinod Kone
>
> 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 a reconcile message to the slave for the tasks.
> → The slave will reply to reconcile messages with the latest state, or 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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