Convert Docker images to Apptainer images
Table of Contents
Why convert your Docker image to an Apptainer image?
While HTCondor can pull container images from Docker Hub, we recommmend converting Docker images to local Apptainer images (.sif files) so that you have a local copy of your container image. This reduces pull requests from Docker Hub.
Convert a Docker image into an Apptainer image
You will need to launch an interactive job to build the Apptainer image. Below is an example of a submit file. You may want to change memory or disk space requirements, depending on the expected requirements for your image.
# build.sub
# For building an Apptainer container
log = build.log
requirements = (HasCHTCStaging == true)
+IsBuildJob = true
request_cpus = 1
request_memory = 4GB
request_disk = 4GB
queue
Submit the interactive job with condor_submit -i build.sub.
[user@ap2002]$ condor_submit -i build.sub
Submitting job(s).
1 job(s) submitted to cluster 3017972.
Waiting for job to start...
Welcome to build1_1@build4000.chtc.wisc.edu!
[user@build4000 ~]$
Once you enter the interactive job, we can begin building the Apptainer image.
Use the apptainer build command to build the Apptainer image.
apptainer build container.sif docker://user/repo:tag
where user/repo:tag is any valid address to a Docker-based container registry. (For example, rocker/tidyverse:4.1.3 from DockerHub or nvcr.io/nvidia/tensorflow:24.02-tf2-py3 from NVIDIA Container Registry.) From this registry, we are creating an Apptainer image called container.sif. After running the command, you should see messages printed to your screen while Apptainer pulls the Docker image and builds the .sif file. The Apptainer image is done building when you see this message:
INFO: Creating SIF file...
INFO: Build complete: container.sif
Move the image to your staging directory
Because container images are generally large, we require users to move these images into their staging directories. While you are still in your interactive job, move the image to your staging directory.
mv container.sif /staging/username/
Use the Apptainer image in a job
To use the Apptainer image in a job, refer to this article: Use Apptainer Containers