Singularity/Apptainer

We support Apptainer/Singularity containers as an alternative way to bring your scientific application to UBELIX instead of installing it using EasyBuild.

If you are familiar with Docker containers, Apptainer containers are essentially the same thing, but are better suited for multi-user HPC systems such as UBELIX. The main benefit of using a container is that it provides an isolated software environment for each application, which makes it easier to install and manage complex applications.

This page provides guidance on preparing your Apptainer containers for use with UBELIX. Please consult the container jobs page for guidance on running your container on UBELIX.

Note

There are two major providers of the apptainer runtime, namely Singularity CE and Apptainer, with the latter being a fork of the former. For most cases, these should be fully compatible. UBELIX provides a Apptainer runtime.

Pulling container images from a registry

Apptainer allows pulling existing container images (Apptainer or Docker) from container registries such as DockerHub. Pulling container images from registries can be done on UBELIX. For instance, the Ubuntu image ubuntu:22.04 can be pulled from DockerHub with the following command:

$ apptainer pull docker://ubuntu:22.04

This will create the Apptainer image file ubuntu_22.04.sif in the directory where the command was run. Once the image has been pulled, the container can be run. Instructions for running the container may be found on the container jobs page.

Take care when pulling container images

Please take care to only use images uploaded from reputable sources as these images can easily be a source of security vulnerabilities or even contain malicious code.

Set cache directories when using Docker containers

When pulling or building from Docker containers using apptainer, the conversion can be quite heavy. You may need to use the scratch filesystem if the build does not succeed in the in-memory filesystem /tmp, i.e. Singularity cache directory, i.e.

$ mkdir -p /scratch/network/users/$USER
$ export APPTAINER_TMPDIR=/scratch/network/users/$USER
$ export APPTAINER_CACHEDIR=/scratch/network/users/$USER

Building Apptainer/Singularity SIF containers

As an example, consider building a container that is compatible with the MPI stack on UBELIX.

Warning

For optimally performing MPI-enabled containers, the application inside the container must be dynamically linked to an MPI version that is compatible with the host MPI.

The following Singularity definition file mpi_osu.def, installs OpenMPI-4.1.5, which is compatible with the Cray-MPICH found on UBELIX. That OpenMPI will be used to compile the OSU micro-benchmarks. Finally, the OSU point to point bandwidth test is set as the “runscript” of the image.

bootstrap: docker
from: ubuntu:22.04

%post
    # Install software
    apt-get update
    apt-get install -y file g++ gcc gfortran make gdb strace wget ca-certificates --no-install-recommends

    # Install OpenMPI
    wget -q https://download.open-mpi.org/release/open-mpi/v4.1/openmpi-4.1.5.tar.gz
    tar xf openmpi-4.1.5.tar.gz
    cd openmpi-4.1.5
    ./configure --prefix=/usr/local
    make -j
    make install
    ldconfig

    # Build osu benchmarks
    wget -q http://mvapich.cse.ohio-state.edu/download/mvapich/osu-micro-benchmarks-5.3.2.tar.gz
    tar xf osu-micro-benchmarks-5.3.2.tar.gz
    cd osu-micro-benchmarks-5.3.2
    ./configure --prefix=/usr/local CC=$(which mpicc) CFLAGS=-O3
    make
    make install
    cd ..
    rm -rf osu-micro-benchmarks-5.3.2
    rm osu-micro-benchmarks-5.3.2.tar.gz

%runscript
    /usr/local/libexec/osu-micro-benchmarks/mpi/pt2pt/osu_bw

The image can be built with

$ apptainer build mpi_osu.sif mpi_osu.def

See the container jobs MPI documentation page for instructions on running this mpi_osu.sif MPI container on UBELIX.