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From "Timothy Chen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MESOS-2368) Provide a backchannel for information to the framework
Date Wed, 18 Feb 2015 08:25:11 GMT

    [ https://issues.apache.org/jira/browse/MESOS-2368?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14325570#comment-14325570
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Timothy Chen commented on MESOS-2368:
-------------------------------------

I'm assuming he means he sends directly from the containerizer back to the framework a seperate
TaskStatus that contains containerizer info. I think they're just using the stock Docker Containerizer
and no custom executor.

> Provide a backchannel for information to the framework
> ------------------------------------------------------
>
>                 Key: MESOS-2368
>                 URL: https://issues.apache.org/jira/browse/MESOS-2368
>             Project: Mesos
>          Issue Type: Improvement
>          Components: containerization, docker
>            Reporter: Henning Schmiedehausen
>            Assignee: Henning Schmiedehausen
>
> So that description is not very verbose. Here is my use case:
> In our usage of Mesos and Docker, we assign IPs when the container starts up. We can
not allocate the IP ahead of time, but we must rely on docker to give our containers their
IP. This IP can be examined through "docker inspect". 
> We added code to the docker containerizer that will pick up this information and add
it to an optional protobuf struct in the TaskStatus message. Therefore, when the executor
and slave report a task as running, the corresponding message will contain information about
the IP address that the container was assigned by docker and we can pick up this information
in our orchestration framework. E.g. to drive our load balancers.
> There was no good way to do that in stock Mesos, so we built that back channel. However,
having a generic channel (not one for four pieces of arbitrary information) from the executor
to a framework may be a good thing in general. Clearly, this information could be transferred
out of band but having it in the standard Mesos communication protocol turned out to be very
elegant.
> To turn our current, hacked, prototype into something useful, this is what I am thinking:
> - TaskStatus gains a new, optional field:
>   - optional TaskContext task_context = 11; (better name suggestions very welcome)
> - TaskContext has optional fields:
>   - optional ContainerizerContext containerizer_context = 1;
>   - optional ExecutorContext executor_context = 2;
> Each executor and containerizer can add information to the TaskContext, which in turn
is exposed in TaskStatus. To avoid crowding of the various fields, I want to experiment with
the nested extensions as described here: http://www.indelible.org/ink/protobuf-polymorphism/
> At the end of the day, the goal is that any piece that is involved in executing code
on the slave side can send information back to the framework along with TaskStatus messages.
Any of these fields should be optional to be backwards compatible and they should (same as
any other messages back) be considered best effort, but it will allow an effective way to
communicate execution environment state back to the framework and allow the framework to react
on it.
> I am planning to work on this an present a cleaned up version of our prototype in a bit.



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