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).
$ apt-get install git devscripts debhelper build-essential
$ git clone https://github.com/spotify/docker-gc.git
$ cd docker-gc
$ debuild -us -uc -bIf you get lintian errors during debuild, try debuild --no-lintian -us -uc -b.
$ dpkg -i ../docker-gc_0.0.4_all.debThis installs the docker-gc script into /usr/sbin. If you want it to
run as a cron job, you can configure it now by dropping a file like this
into /etc/cron.hourly/.
#!/bin/bash
/usr/sbin/docker-gc
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.
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
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
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
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 currently built with Docker 1.6.2, 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 .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 -d --name docker-gc -v $(which docker):/bin/docker:ro -v /var/run/docker.sock:/var/run/docker.sock --log-driver=fluentd --log-opt 'fluentd-tag=docker.docker-gc' wehkamp/docker-gc:1.0The /etc directory is also mapped so that it can read any exclude files
that you've created.