Build containers

The standard SingularityCE way to build .sif containers is from .def definition files.

Definition file

Rat-Containers contains several SingularityCE Definition Files available on GitLab at rat-containers/singularityCE.

These files follow a general structure:

example.def

# Header section
# To boostrap from local image, first run:
#   singularity pull <agent>://<provider>/<name>.sif
# and point to this image with the following header.
Bootstrap: localimage
From: ./<name>.sif
# Otherwise to use provider directly:
# Bootstrap: <agent>
# From: <provider>/<name>.sif

# Commands to run post creation of the OS in container
%post

    # Common steps are:
    # 1. Update package manager and packages
    apt-get update

    # 2. Install dependencies and setup environment
    apt-get install -y xeyes

    # 3. Build desired packages
    make stuff-up

    # 4. Clean-up
    rm -rf cache

# Scripts to run for `singularity run <container> [<args>]`
# Will be used to print info and exit in Rat-Containers cases
%runscript

    # Script to run, if needed
    echo "Cycling..."

# Metadata: printed by `singularity inspect <container>`
%labels

    # Key value pairs defining labels, parsed as:
    <attribute> <value>

    # e.g.
    author vacuuous.rom@byrg.com
    program.version 1.0.0

# Help: printed by `singularity run-help <container>`
# Raw text to print to the console
%help
SingularityCE Definition File structure example

Check out Rat-Containers on GitLab:
https://gitlab.com/project-rat-extras/rat-containers

Build command

These files can then be used to build containers like so:

sudo singularity build --force <container>.sif <definition_file>.def

Note

The --force flag overwrite labels and metadata from previous images if bootstrapped from them.

Chaining images

Building containers from scratch can get quite cumbersome iterations after iterations. Moreover one might need to acquire a custom base image to bootstrap from for different containers.

One solution to this is “chaining images”:

• Bootstrap from online base image of interest (e.g. Rocky Linux 8 with CUDA) to generate local image with complete desired environment.

• Bootstrap from generated local image and so on and so forth.

Note

The rat-containers/singularityCE directory contains chained images for Project-Rat and for pyRat. One could of course “flatten” the recipes in order to have a full self contained definition file for their container instead of building each one of them incrementally.