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From "Jim Brennan (JIRA)" <j...@apache.org>
Subject [jira] [Created] (YARN-8656) container-executor should not write cgroup tasks files for docker containers
Date Mon, 13 Aug 2018 19:57:00 GMT
Jim Brennan created YARN-8656:
---------------------------------

             Summary: container-executor should not write cgroup tasks files for docker containers
                 Key: YARN-8656
                 URL: https://issues.apache.org/jira/browse/YARN-8656
             Project: Hadoop YARN
          Issue Type: Bug
            Reporter: Jim Brennan


If cgroups are enabled, we pass the {{--cgroup-parent}} option to {{docker run}} to ensure
that all processes for the container are placed into a cgroup under (for example) {{/sys/fs/cgroup/cpu/cgroups.hierarchy/container_id}}.
Docker creates a cgroup there with the docker container id as the name and all of the processes
in the container go into that cgroup.

container-executor has code in {{launch_docker_container_as_user()}} that then cherry-picks
the PID of the docker container (usually the launch shell) and writes that into the {{/sys/fs/cgroup/cpu/cgroups.hierarchy/container_id/tasks}} file,
effectively moving it from {{/sys/fs/cgroup/cpu/cgroups.hierarchy/container_id/docker_container_id}} to {{/sys/fs/cgroup/cpu/cgroups.hierarchy/container_id}}. 
So you end up with one process out of the container in the {{container_id}} cgroup, and
the rest in the {{container_id/docker_container_id}} cgroup.

Since we are passing the {{--cgroup-parent}} to docker, there is no need to manually write
the container pid to the tasks file - we can just remove the code that does this in the docker
case.



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