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Last pushed: a day ago
Short Description
Garbage collection of Docker containers and images
Full Description

docker-gc

A simple Docker container and image garbage collection script.

  • Containers that exited more than an hour ago are removed.
  • Images that don't belong to any remaining container after that are removed.

Although docker normally prevents removal of images that are in use by
containers, we take extra care to not remove any image tags (e.g., ubuntu:14.04,
busybox, etc) that are in use by containers. A naive docker rmi $(docker images -q) will leave images stripped of all tags, forcing docker to re-pull the
repositories when starting new containers even though the images themselves are
still on disk.

This script is intended to be run as a cron job, but you can also run it as a Docker
container (see below).

Building the Debian Package

$ apt-get install git devscripts debhelper build-essential dh-make
$ git clone https://github.com/spotify/docker-gc.git
$ cd docker-gc
$ debuild -us -uc -b

If you get lintian errors during debuild, try debuild --no-lintian -us -uc -b.

Installing the Debian Package

$ dpkg -i ../docker-gc_0.1.0_all.deb

This installs the docker-gc script into /usr/sbin. If you want it to
run as a cron job, you can configure it now by creating a root-owned
executable file /etc/cron.hourly/docker-gc with the following contents:

#!/bin/bash
/usr/sbin/docker-gc

To test that the job will actually run you can use this command

run-parts --test /etc/cron.hourly

Manual Usage

To use the script manually, run docker-gc. The system user under
which docker-gc runs needs to have read and write access to
the $STATE_DIR environment variable which defaults to /var/lib/docker-gc.

Excluding Images From Garbage Collection

There can be images that are large that serve as a common base for
many application containers, and as such, make sense to pin to the
machine, as many derivative containers will use it. This can save
time in pulling those kinds of images. There may be other reasons to
exclude images from garbage collection. To do so, create
/etc/docker-gc-exclude, or if you want the file to be read from
elsewhere, set the EXCLUDE_FROM_GC environment variable to its
location. This file can contain image name patterns (in the grep
sense), one per line, such as spotify/cassandra:latest or it can
contain image ids (truncated to the length shown in docker images
which is 12.

An example image excludes file might contain:

spotify/cassandra:latest
redis:.*
9681260c3ad5

Excluding Containers From Garbage Collection

There can also be containers (for example data only containers) which
you would like to exclude from garbage collection. To do so, create
/etc/docker-gc-exclude-containers, or if you want the file to be
read from elsewhere, set the EXCLUDE_CONTAINERS_FROM_GC environment
variable to its location. This file should container name patterns (in
the grep sense), one per line, such as mariadb-data.

An example container excludes file might contain:

mariadb-data
drunk_goodall

Forcing deletion of images that have multiple tags

By default, docker will not remove an image if it is tagged in multiple
repositories.
If you have a server running docker where this is the case, for example
in CI environments where dockers are being built, re-tagged, and pushed,
you can enable a force flag to override this default.

FORCE_IMAGE_REMOVAL=1 docker-gc

Preserving a minimum number of images for every repository

You might want to always keep a set of the most recent images for any
repository. For example, if you are continually rebuilding an image during
development you would want to clear out all but the most recent version of an
image. To do so, set the MINIMUM_IMAGES_TO_SAVE=1 environment variable. You
can preserve any count of the most recent images, e.g. save the most recent 10
with MINIMUM_IMAGES_TO_SAVE=10.

Forcing deletion of containers

By default, if an error is encountered when cleaning up a container, Docker
will report the error back and leave it on disk. This can sometimes lead to
containers accumulating. If you run into this issue, you can force the removal
of the container by setting the environment variable below:

FORCE_CONTAINER_REMOVAL=1 docker-gc

Excluding Recently Exited Containers and Images From Garbage Collection

By default, docker-gc will not remove a container if it exited less than 3600 seconds (1 hour) ago. In some cases you might need to change this setting (e.g. you need exited containers to stick around for debugging for several days). Set the GRACE_PERIOD_SECONDS variable to override this default.

GRACE_PERIOD_SECONDS=86400 docker-gc

This setting also prevents the removal of images that have been created less than GRACE_PERIOD_SECONDS seconds ago.

Dry run

By default, docker-gc will proceed with deletion of containers and images. To test your command-line options set the DRY_RUN variable to override this default.

DRY_RUN=1 docker-gc

Running as a Docker Image

A Dockerfile is provided as an alternative to a local installation. By default
the container will start up, run a single garbage collection, and shut down.

The image is published as spotify/docker-gc.

Building the Docker Image

The image is currently built with Docker 1.12.4, but to build it against a newer
Docker version (to ensure that the API version of the command-line interface
matches with your Docker daemon), simply edit the ENV DOCKER_VERSION line in
Dockerfile
prior to the build step below.

Build the Docker image with make -f Makefile.docker image or:

docker build -t spotify/docker-gc .

Running as a Docker Container

The docker-gc container requires access to the docker socket in order to
function, so you need to map it when running, e.g.:

$ docker run --rm -v /var/run/docker.sock:/var/run/docker.sock -v /etc:/etc:ro spotify/docker-gc

The /etc directory is also mapped so that it can read any exclude files
that you've created.

If your docker daemon is configured to run with user namespace, you will need to
run the container with user namespace disabled:

$ docker run --rm --userns host -v /var/run/docker.sock:/var/run/docker.sock -v /etc:/etc spotify/docker-gc
Docker Pull Command
Owner
spotify
Source Repository

Comments (1)
ruudud
a year ago

The latest build failed for some reason, so the DRY_RUN option is unavailable.