docker-flatten-image.sh: flattens docker images

docker-flatten-image.sh

#!/bin/sh

# The MIT License (MIT)
# Copyright (c) 2016 Chris Olstrom <chris@olstrom.com>

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:

# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.

# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.

set -o errexit -o nounset -o pipefail -o xtrace

NAMESPACE=${NAMESPACE:-$(pwd | xargs dirname | xargs basename)}
IMAGE=${IMAGE:-$(pwd | xargs basename)}

REPOSITORY=${NAMESPACE}/${IMAGE}

stage1() {
    docker build -t ${REPOSITORY}:stage1 .
    STAGE1=$(docker images | awk "\$1 == \"${REPOSITORY}\" && \$2 == \"stage1\" { print \$3 }" | head -n 1)
}

stage2() {
    docker run --entrypoint /bin/true ${STAGE1}
    CONTAINER=$(docker ps --quiet --latest --filter ancestor=${STAGE1})
    docker export ${CONTAINER} | docker import - ${REPOSITORY}:stage2
}

stage3() {
    {
        echo "FROM ${REPOSITORY}:stage2"
        grep -E '^(ENTRYPOINT|CMD)' Dockerfile
    } | docker build -t ${REPOSITORY}:stage3 -
}

tag() {
    docker tag ${REPOSITORY}:stage3 ${REPOSITORY}:latest
}

stage1 && stage2 && stage3 && tag