Exporting charliecloud tarballs from docker

Introduction

This post is about how one can build and export charliecloud images from a docker daemon running on your local system. For more details about charliecloud and how to get Rstudio running with it you can have a look at my other blog post.

Exporting tar-balls from Docker

This is in actuality rather straight forward. You have to have docker installed on your system and the docker service/daemon needs to be running.

Here is an example on how you can build a container, simply call the docker build command from a terminal window and provide the path to the dockerfile via -f <./path/to/file> and a nice name via -t <name>):

docker build -f ./dockerfiles/my_dockerfile -t nice_name .

Don’t forget the . at the end of the command, otherwise docker will complain.

NOTE: Avoid putting large files in the directory from which you start the build. Docker will send all files in the working directory to the build context which can take a long while. Therefore, also export your images to a different directory outside of the current one.

Now, to package the built image as a charliecloud-readable image tar-ball, you need to first docker create your image and then docker export it to a *.tar-file. Finally, you can gzip it to save some space, like so:

# where to put the image file

mkdir ../images/

# create image and save its id

id=$(docker create nice_name)
docker export $id > ../images/nice_name.tar
gzip -c ../images/nice_name.tar > ../images/nice_name.tar.gz

The resulting tar.gz (in this example nice_name.tar.gz) file can then be transferred to e.g. a HPC server running charliecloud to make your very own software stack available there.

Putting it together

Naturally, the above commands can also be combined to make it even more straight forward to use:

mkdir ../images/

# save the name in a variable

image_name='nice_name'

docker build -f ./dockerfiles/my_dockerfile -t ${image_name} . && \

  docker export $(docker create ${image_name}) | \

  gzip -c > ../images/${image_name}.tar.gz

Wrap the above commands in a nice script (e.g. export_image.sh) to make your export as easy as possible!

Summary

That’s all! A straight-forward way to bundle your favourite docker image into a charliecloud readable tar-ball. See you next time!

Until then, farewell!