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customization.md

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Customization of DockerRoot

You can customize DockerRoot by modifing files in ./configs/ and ./scripts/. And also you can customize the pre-built DockerRoot image on the fly as below.

Making a persistent disk for DockerRoot

Because DockerRoot runs from RAM, you need to create an additional disk to make your customization persistent.

The disk must be formated with ext4 and have the label DOCKERROOT-DATA to be mounted automatically.

Ex.) $ sudo mkfs.ext4 -b 4096 -i 4096 -F -L DOCKERROOT-DATA /dev/xxx

Note) You can use any numbers for -b 4096 -i 4096, but pay attention to excessive inode usage because DockerRoot uses overlay for Docker storage.

Cf.)

And also you can create a swap disk with the label DOCKERROOT-SWAP to be activated automatically.

Ex.) $ sudo mkswap -L DOCKERROOT-SWAP /dev/xxx

Customizing the behavior of the Docker daemon

You can customize the behavior of the Docker daemon through /var/lib/docker-root/profile.

Defaults

  • DOCKER_STORAGE="overlay"
  • DOCKER_DIR="/var/lib/docker"
  • DOCKER_HOST="-H unix://"
  • DOCKER_EXTRA_ARGS="--userland-proxy=false"
  • DOCKER_ULIMITS=1048576
  • DOCKER_LOGFILE="/var/lib/docker-root/docker.log"
  • DOCKER_TIMEOUT=5

You can override these defaults by puting the above variables into profile. Then DockerRoot uses them to execute Docker daemon in /etc/init.d/docker as below.

ulimit -n ${DOCKER_ULIMITS}
ulimit -u ${DOCKER_ULIMITS}

/opt/bin/docker daemon -D -s ${DOCKER_STORAGE} -g "${DOCKER_DIR}" ${DOCKER_HOST} ${DOCKER_EXTRA_ARGS} >> "${DOCKER_LOGFILE}" 2>&1

Ex.) To expose the Docker post 2375,

$ cat /var/lib/docker-root/profile
DOCKER_HOST="-H unix:// -H tcp://0.0.0.0:2375"

Cf.)

Customizing init scripts on booting up

You can customize init scripts in three ways as below.

  • Putting any scripts in the /etc/init.d/S* in the SysV manner.
  • DockerRoot's init executes /var/lib/docker-root/init.sh right after mounting the disk and before init.d scripts including networking.
  • DockerRoot's init executes /var/lib/docker-root/start.sh asynchronously right before executing Docker.

Cf.)

And also you can edit any files in /etc, because /etc is mounted at the persistent disk with overlay if the disk exists.