How to generate a Dockerfile from an image?

Question

Is it possible to generate a Dockerfile from an image? I want to know for two reasons:

1. I can download images from the repository but would like to see the recipe that generated them.

2. I like the idea of saving snapshots, but once I am done it would be nice to have a structured format to review what was done.

Answer 1

How to generate or reverse a Dockerfile from an image?

You can. Mostly.

Notes: It does not generat a Dockerfile that you can use directly with docker build, the output is just for your reference.

alias dfimage="docker run -v /var/run/docker.sock:/var/run/docker.sock --rm alpine/dfimage" dfimage -sV=1.36 nginx:latest 

It will pull the target docker image automaticlaly and export Dockerfile. Parameter -sV=1.36 is not always required.

Reference: https://hub.docker.com/repository/docker/alpine/dfimage

Now hub.docker.com shows the image layers with detail commands directly, if you choose a particular tag.

Bonus

If you want to know which files are changed in each layer

alias dive="docker run -ti --rm  -v /var/run/docker.sock:/var/run/docker.sock wagoodman/dive" dive nginx:latest 

On the left, you see each layer's command, on the right (jump with tab), the yellow line is the folder that some files are changed in that layer

(Use SPACE to collapse dir)

Old answer

below is the old answer, it doesn't work any more.

$ docker pull centurylink/dockerfile-from-image $ alias dfimage="docker run -v /var/run/docker.sock:/var/run/docker.sock --rm centurylink/dockerfile-from-image" $ dfimage --help Usage: dockerfile-from-image.rb [options] <image_id>     -f, --full-tree                  Generate Dockerfile for all parent layers     -h, --help                       Show this message