There is a dependency between job submitting user and the user in the Docker image in LCE currently. For instance, in order to run the Docker container as yarn user, we can choose set the "yarn.nodemanager.linux-container-executor.nonsecure-mode.local-user" to yarn and leave "yarn.nodemanager.linux-container-executor.nonsecure-mode.limit-users" default (true). Then LCE will choose yarn ( UID maybe 1001) as the user running jobs.
LCE will mount the generated launch_container.sh (owned by the running job user) and /etc/passwd (current the code is mounting to container's /etc/password, I think it's a mistake) into the Docker container and utilizes "docker run --user=<run_as_user>" option to get it done internally.
Mounting /etc/passwd to the container is a not good choice due to override original users defined in Docker image. As far as I know, since Docker v1.8 (or maybe earlier), the Docker run command "--user=" option accepts UID and when passing UID, the user does not have to exist in the container. So we could use UID instead of user name to construct the Docker run command to eliminate the dependency that create the same user in the Docker image. This enables LCE the ability to launch any Docker container safely regardless what users in it.
But this is not enough to decouple host user and Docker container user. The final solution we are searching for are focused on allowing users to run their Docker images flexibly without involving dependencies of YARN and make sure the container won't bring in security risk.