Dump/Extract a Docker Image Layers

docker_dump.sh

################################################################################
# A simple script for dumping the layers of a docker image.
#
# Dependencies:
#   * docker (duh)
#   * jq (https://stedolan.github.io/jq/)
#
# Usage
# ./docker_dump.sh DOCKER_IMAGE_NAME
#
################################################################################

#!/usr/bin/env bash

# Allow the image to be passed in as a variable
DOCKER_IMAGE_URL=$1

# Define where we'll save all the output
EXTRACTION_DIR=$(echo $DOCKER_IMAGE_URL|sed 's#[.:/]#_#g')

# Create the output dir
mkdir -p $EXTRACTION_DIR

# Pull the image
docker pull $DOCKER_IMAGE_URL

# Dump the image to a tar file & extract it
DOCKER_TAR="${EXTRACTION_DIR}/image.tar"
docker save $DOCKER_IMAGE_URL -o $DOCKER_TAR
tar -xf $DOCKER_TAR -C $EXTRACTION_DIR

# Get a list of layers in the docker image
$LAYERS=$(cat "${EXTRACTION_DIR}/manifest.json"|jq -r '.[].Layers[]')

# Iterate over the layers, and extract them
for layer in $LAYERS; do
  LAYER_PATH="${EXTRACTION_DIR}/${layer}"
  LAYER_DIR=$(dirname $LAYER_PATH)
  LAYER_NAME=$(basename $LAYER_DIR)
  LAYER_EXTRACTION_DIR="${LAYER_DIR}/extracted"

  mkdir -p $LAYER_EXTRACTION_DIR
  tar -xf $LAYER_PATH -C $LAYER_EXTRACTION_DIR
done

# Finally, print out everything we just extracted
find $EXTRACTION_DIR