#tech/docker

Docker Reverse Engineering

Use dfimage to "reverse engineer" the Dockerfile.

# "install" dfimage
docker pull ghcr.io/laniksj/dfimage
alias dfimage='docker container run --rm -v /var/run/docker.sock:/var/run/docker.sock ghcr.io/laniksj/dfimage'

# the image you want to analyze MUST be present locally
docker image pull ${image}:${tag}

# when passing the image, you MUST specify the tag
dfimage ${image}:${tag}

It won't be explicit. Here are some inconsistencies you may find:

it'll show some hashes instead of filenames
it won't show the image used as a base (the image in the FROM)
right after the FROM it'll show an ADD directive, that probably is not useful for our purposes

The resulting Dockerfile is still enigmatic, then we'll use dive to analyze each layer and check which files were changed on each layer.

# "install" dive
docker image pull wagoodman/dive:latest
alias dive='docker container run --rm -it -v /var/run/docker.sock:/var/run/docker.sock wagoodman/dive:latest'

# run it
dive ${image}:${tag}

Check the hotkeys in the bottom and find a way to filter only changes for each layer.

Docker Reverse Engineering

references

see also