Using Docker Images with Apptainer

So far, we have used container images that are already available on Torch under /share/apps/images.

In practice, you may also want to run software that is not provided by the cluster. Apptainer can pull images directly from Docker registries and convert them into the Apptainer SIF format.

warning

Pulling container images can require significant network bandwidth and disk space. On Torch, image downloads should be performed on compute nodes rather than login nodes.

For example, we can pull an official PyTorch image from Docker Hub:

apptainer pull pytorch.sif docker://pytorch/pytorch:latest

During the pull process, Apptainer downloads the Docker image layers and converts them into a single SIF image:

INFO:    Converting OCI blobs to SIF format
INFO:    Starting build...
INFO:    Fetching OCI image...
...
INFO:    Creating SIF file...

The output shows that Apptainer is downloading the Docker image layers and converting them into a single SIF image. Once the conversion completes, the resulting SIF file can be used without Docker. When the command completes, a new image named pytorch.sif will be created in the current directory.

You can verify that the image exists:

ls -lh pytorch.sif

The image can now be used like any other Apptainer image.

For example:

apptainer exec pytorch.sif python --version

or

apptainer exec pytorch.sif python -c "import torch; print(torch.__version__)"