Docker image size reducer

Using a Docker give us great opportunity to move server instances from one machine to another in cloud or in bare metal servers, but sometimes it’s has some price like storage that Docker use. For example after moving one of my Docker instances with creating images it was using 3+GB so I figure out how to reduce this state to acceptable size of 670 MB.

The solution is export a Docker image and import it back. I wrote two bash functions which make those actions. The both functions are making same things. First one use containers as entry point and second one use already created images.

Warning: This will delete all previous versions of this Docker instance.

# Reduce docker image size by removing history of image
function docker-image-reduce-by-container() {
        DOCKER_CONTAINER_ID=$1
        DOCKER_NEW_IMAGE_NAME=$2
        if [ ${#DOCKER_CONTAINER_ID} == 0 ]; then
                echo "Current container id is required as first parameter."; exit
        elif [ ${#DOCKER_NEW_IMAGE_NAME} == 0 ]; then
                echo "New image name is required as secund parameter."; exit
        fi
        TMP_FILE_PATH='/tmp/docker-image-size-reducer-by-container-'$(date | md5sum | awk '{print $1}')'.tar'
        docker export $DOCKER_CONTAINER_ID > $TMP_FILE_PATH
        cat $TMP_FILE_PATH | docker import - $DOCKER_NEW_IMAGE_NAME
        rm $TMP_FILE_PATH
}


# Reduce docker image size by removing history of image
function docker-image-reduce-by-image() {
        DOCKER_CURRNT_IMAGE_NAME=$1
        DOCKER_NEW_IMAGE_NAME=$2
        if [ ${#DOCKER_CURRNT_IMAGE_NAME} == 0 ]; then
                echo "Current container image name is required as first parameter."; exit
        elif [ ${#DOCKER_NEW_IMAGE_NAME} == 0 ]; then
                echo "New image name is required as secund parameter."; exit
        fi
        TMP_FILE_PATH='docker-image-size-reducer-by-image-'$(date | md5sum | awk '{print $1}')
        docker run --name="$TMP_FILE_PATH" $DOCKER_CURRNT_IMAGE_NAME
        docker-reduce-by-container $TMP_FILE_PATH $DOCKER_NEW_IMAGE_NAME
}

Example of usage:

docker-image-reduce-by-container "your-current-container" "your-new-image"
docker-image-reduce-by-image "your-current-image" "your-new-image"

This can be used by copy/paste in command line or if you are doing it frequently just add them into your ~/.bashrc file.