Henning Schmiedehausen created MESOS-2368:
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Summary: 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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