How to remove old docker images in continuous integration to save disk space

Question

When building docker images in a continuous integration environment, you quickly run out of disk space and need to remove old images. However, you can't remove all the old images, including intermediate images, because that breaks caching.

How do you avoid running out of disk space on your build agents, without breaking caching?

Answer 1

My solution is to remove the previous version of the image after building the new one. This ensures that cached images are available to speed up the build, but avoids old images piling up and eating your disk space. This method relies on each version of the image having a unique tag.

This is my script (gist here ):

#!/usr/bin/env bash

usage(){
# ============================================================
echo This script removes all images of the same repository and
echo older than the provided image from the docker instance.
echo
echo This cleans up older images, but retains layers from the
echo provided image, which makes them available for caching.
echo
echo Usage:
echo
echo '$ ./delete-images-before.sh <image-name>:<tag>'
exit 1
# ============================================================
}

[[ $# -ne 1 ]] && usage

IMAGE=$(echo $1 | awk -F: '{ print $1 }')
TAG=$(echo $1 | awk -F: '{ print $2 }')

FOUND=$(docker images --format '{{.Repository}}:{{.Tag}}' | grep ${IMAGE}:${TAG})

if ! [[ ${FOUND} ]]
then
    echo The image ${IMAGE}:${TAG} does not exist
    exit 2
fi

docker images --filter before=${IMAGE}:${TAG} \
    | grep ${IMAGE} \
    | awk '{ print $3 }' \
    | xargs --no-run-if-empty \
    docker --log-level=warn rmi --force || true

Answer 2

A tool we use to handle this is docker custodian (dcgc).

It is suggested to keep a list of images that you want to keep around and never clean up and pass that to --exclude-image (If you're using puppet or some other resource management system, it may be more useful to write a file to disk that contains the image patterns and instead use --exclude-image-file )