Building an image without a Dockerfile

It is also possible to build an image without a Dockerfile, "freezing" the state of a container with docker container commit. It is useful for quick experiments, but it is not reproducible — for anything serious, prefer a Dockerfile.

Enter an interactive container:

docker container run --interactive --tty --name my-ubuntu ubuntu /bin/bash

Inside the container, make whatever changes you want — install packages, create files, etc.:

apt-get update && apt-get install -y curl

Leave the container (exit). It stays stopped, but preserved. Now build an image from it:

docker container commit \
  --message "add curl" \
  --author "Rafael Dutra <[email protected]>" \
  my-ubuntu workshop/ubuntu-curl:0.1

Check that the image exists and run a container from it:

docker image ls workshop/ubuntu-curl
docker container run --rm workshop/ubuntu-curl:0.1 curl --version

Notice the problem: whoever looks at this image has no way of knowing what was done or of redoing the process. With a Dockerfile, the history is versioned and anyone can rebuild the same image with docker build.