wrap up

Since it can not be extracted directly from the image, start the container as follows and copy it with docker cp

CONTAINER_ID=`docker create $IMAGE_NAME`
docker cp $CONTAINER_ID:$FILEPATH .

background

You may want to retrieve the source code or files in an Image that you have deployed for bugs or spec investigation. I have summarized the procedure of what to do at that time.

Find the target file path

All you need to know is the path to the target file or directory, but if not, you'll need to look inside to find what you're looking for.

Search using the shell

It should contain / bin / bash and / bin / sh, so use it to find files interactively. docker run --rm -it $IMAGE_NAME /bin/bash

If it is not included, you can use it as the base image of the Dockerfile and create an installed image.

Look for the difference for each layer with dive

You can see the file tree for each layer by using dive. If you know that it was added in a particular layer, you may find it faster. dive $IMAGE_NAME

The following article will be helpful for how to use dive. https://qiita.com/t_o_d/items/625ad7a274ca34be3312

Copy the target file

It seems that files cannot be extracted directly from the image. Therefore, you can copy the files and folders by starting the container and copying with docker cp as shown below.

# IMAGE_Set the target image name in NAME and the file path in the Docker Image of the target file in FILEPATH.
IMAGE_NAME=me/my_application:1.0.0
FILEPATH=/app/scripts/woker/

CONTAINER_ID=`docker create $IMAGE_NAME`
docker cp $CONTAINER_ID:$FILEPATH .
docker rm $CONTAINER_ID