docker-rebase

#!/bin/bash
# Script to convert a docker container to an image without history
# Copyright (C) 2014 docbill@gmail.com

#   This program is free software: you can redistribute it and/or modify
#   it under the terms of the GNU General Public License as published by
#   the Free Software Foundation, either version 3 of the License, or
#   (at your option) any later version.
#
#   This program is distributed in the hope that it will be useful,
#   but WITHOUT ANY WARRANTY; without even the implied warranty of
#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#   GNU General Public License for more details.
# 
#   You should have received a copy of the GNU General Public License
#   along with this program.  If not, see <http://www.gnu.org/licenses/>.

# This is an alternative to docker commit that will create a new image
# without history.  Rebuilding the Dockerfile from an existing container is
# tricky.  Currently the CMD is not parsed correctly, but it is probably close
# enough to work with most containers.  There are probably other errors as
# as well, as docker history is an in-precise way to learn the original 
# docker commands.

if [ -z "$1" -o -z "$2" ]
then
  echo "$0 CONTAINER REPOSITORY[:TAG]" 1>&2
  echo " "
  echo "$0 is an alternative to docker commit to create new image without"
  echo "all the revision history."
  exit 1
fi

# This is a sad story.  Since a container name and an image name can be the
# same we have to use docker ps to find the container id.   That is not as easy
# as it seems if you want to be "fool proof".

re=$((docker ps -a -q --no-trunc --before="$1" ;docker ps -a -q --no-trunc --since="$1")|sort -u|tr '\n' '|')
containerId=$(docker ps --no-trunc -a -q | egrep -v "^($re)\$")
imageId=$(docker inspect --format '{{.Image}}' "$containerId")

if [ -n "$imageId" ]
then
  echo "Exporting and importing the container to a new image"
  from=$(docker export "$containerId" | docker import -)
  echo " ---> $from"
  if [ -z "$from" ]
  then 
    echo "Failed to export and import $containerId" 1>&2
    exit 1
  fi
  # Inspect the existing image to create a Dockerfile
  (
    echo "From $from"
    (
      docker history --no-trunc "$imageId" | \
      sed -n -e 's,.*/bin/sh -c #(nop) \(MAINTAINER .*[^ ]\) *0 B,\1,p' | \
      head -1
    )
    (
      format='{{range $e := .Config.Env}}
ENV {{$e}}
{{end}}{{range $e,$v := .Config.ExposedPorts}}
EXPOSE {{$e}}
{{end}}{{range $e,$v := .Config.Volumes}}
VOLUME {{$e}}
{{end}}{{with .Config.User}}USER {{.}}{{end}}
{{with .Config.WorkingDir}}WORKDIR {{.}}{{end}}
{{with .Config.Entrypoint}}ENTRYPOINT {{json .}}{{end}}
{{with .Config.Cmd}}CMD {{json .}}{{end}}
{{with .Config.OnBuild}}ONBUILD {{json .}}{{end}}'

      docker inspect --format="$format" "$imageId" | \
      sed -e 's,^\(ENV [^=]*\)=,\1 ,' \
        -e 's,^\(EXPOSE [0-9]*\)/tcp,\1,' | \
      awk '{if (tolower($1) ~/env/) {v=$3;for(i=4;i<=NF;i++){v=v"\\ "$i};E[$2]=v} else print} END {r="ENV ";for (i in E) r=r" "i"="E[i];print r}'
    )
  ) | docker build --force-rm -t "$2" -
  status=$?
  # We only successfully remove the image if the build failed.
  docker rmi "$from" 2>>/dev/null
  exit $status
else
    echo "Failed to to find image id" 1>&2
    exit 1
fi