Chapter 24. Using Podman in HPC environment You can use Podman with Open MPI (Message Passing Interface) to run containers in a High Performance Computing (HPC) environment. 24.1. Using Podman with MPI The example is based on the ring.c program taken from Open MPI. In this example, a value is passed around by all processes in a ring-like fashion. Each time the message passes rank 0, the value is decremented. When each process receives the 0 message, it passes it on to the process and then quits. By passing the 0 first, every process gets the 0 message and can quit normally. Prerequisites The container-tools module is installed. Procedure Install Open MPI: To activate the environment modules, type: Load the mpi/openmpi-x86_64 module: Optionally, to automatically load mpi/openmpi-x86_64 module, add this line to the .bashrc file: To combine mpirun and podman , create a container with the following definition: Build the container: Start the container. On a system with 4 CPUs this command starts 4 containers: As a result, mpirun starts up 4 Podman containers and each container is running one instance of the ring binary. All 4 processes are communicating over MPI with each other. Additional resources Podman in HPC environments 24.2. The mpirun options The following mpirun options are used to start the container: --mca orte_tmpdir_base /tmp/podman-mpirun line tells Open MPI to create all its temporary files in /tmp/podman-mpirun and not in /tmp . If using more than one node this directory will be named differently on other nodes. This requires mounting the complete /tmp directory into the container which is more complicated. The mpirun command specifies the command to start, the podman command. The following podman options are used to start the container: run command runs a container. --env-host option copies all environment variables from the host into the container. -v /tmp/podman-mpirun:/tmp/podman-mpirun line tells Podman to mount the directory where Open MPI creates its temporary directories and files to be available in the container. --userns=keep-id line ensures the user ID mapping inside and outside the container. --net=host --pid=host --ipc=host line sets the same network, PID and IPC namespaces. mpi-ring is the name of the container. /home/ring is the MPI program in the container. Additional resources Podman in HPC environments

Commands:
yum install openmpi
. /etc/profile.d/modules.sh
module load mpi/openmpi-x86_64
echo "module load mpi/openmpi-x86_64" >> .bashrc
cat Containerfile FROM registry.access.redhat.com/ubi8/ubi RUN yum -y install openmpi-devel wget && yum clean all RUN wget https://raw.githubusercontent.com/open-mpi/ompi/master/test/simple/ring.c && /usr/lib64/openmpi/bin/mpicc ring.c -o /home/ring && rm -f ring.c
podman build --tag=mpi-ring .
mpirun --mca orte_tmpdir_base /tmp/podman-mpirun podman run --env-host -v /tmp/podman-mpirun:/tmp/podman-mpirun --userns=keep-id --net=host --pid=host --ipc=host mpi-ring /home/ring Rank 2 has cleared MPI_Init Rank 2 has completed ring Rank 2 has completed MPI_Barrier Rank 3 has cleared MPI_Init Rank 3 has completed ring Rank 3 has completed MPI_Barrier Rank 1 has cleared MPI_Init Rank 1 has completed ring Rank 1 has completed MPI_Barrier Rank 0 has cleared MPI_Init Rank 0 has completed ring Rank 0 has completed MPI_Barrier