Managing Combinatorial Software Installations with Spack

HPC centers deploy a variety of scientific software, but the complexity of building scientific applications makes package management increasingly difficult. Users demand combinatorial versions of packages, but site administrators may need to perform in-place upgrades for security and for bug fixes.This paper describes an extension of the Spack package manager that allows HPC centers to navigate a compromise between fully combinatorial versioning and a stable, upgradable software stack. Spack provides a set of templated packages that can be deployed in arbitrarily many combinatorial build configurations. We introduce subspaces, an extension of Spack's versioning system that allows HPC sites to choose an arbitrary combinatorial complexity for packages they deploy. Subspaces allow us to use a single Spack package to generate binary packages for systems such as RPM. Using subspaces, support staff can configure the degree of combinatorial versioning exposed to the user. This capability enables an intuitive and flexible user environment that can be leveraged across multiple HPC sites.