Is it possible to generate a Dockerfile from an image?

To understand how a docker image was built, use the command:

$ docker history --no-trunc <IMAGE_ID>

You can build a docker file from an image, but it will not contain everything you would want to fully understand how the image was generated. Reasonably what you can extract is the:

• MAINTAINER,
• ENV,
• EXPOSE,
• VOLUME,
• WORKDIR,
• ENTRYPOINT,
• CMD,
• ONBUILD

parts of the dockerfile.