dockerdiff

#!/bin/bash

# Compare two docker images, reporting what changed.
# The script will exit 1 if there are differences between the images
# other than their tags.
#
# It will also try and show what the differences are, comparing
#  - the image config
#  - the installed dpkg packages
#  - changed file metadata
#  - changed file checksums

set -e
set -u
set -o pipefail

IMAGE1=$1
IMAGE2=$2

inspect() {
    docker inspect $1 | jq ".[0]|del(.RepoTags,.RepoDigests)"
}

dpkgl() {
    docker run --rm $1 dpkg -l
}

lslr() {
    docker run --rm $1 bash -c 'find / -xdev -not -path /proc -a -not -path /sys -print0 | sort -z | xargs -0 ls -ld'
}

md5() {
    docker run --rm $1 bash -c 'find / -xdev -not -path /etc/hosts -a -not -path /etc/hostname -a -type f -print0 | sort -z | xargs -0 md5sum'
}

_diff() {
    local cmd=$1
    diff -u --label $IMAGE1 --label $IMAGE2 <($cmd $IMAGE1)  <($cmd $IMAGE2)
}

if ! _diff inspect; then
    _diff dpkgl || true
    _diff lslr || true
    _diff md5 || true
    exit 1
fi