One of the challenges in HPC is to deliver a consistent software stack that balances the needs of the system administrators with the needs of the users. This means running recent software on enterprise Linux distributions that ship older software. Traditionally this is accomplished using environment modules, that change environment variables such as $PATH to point to the software that is needed. At Compute Canada we have taken this further by distributing a complete user-level software stack, including all needed libraries including the GNU C library (Glibc), but excluding any privileged components. Our setup combined Nix, and now combines Gentoo Prefix for the bottom layer of base components, EasyBuild for the top layer of more scientifically inclined components, Lmod to implement environment modules, and the CernVM File System (CVMFS) to distribute it to Canadian supercomputers and anyone else who is interested. This approach has gained interest in other places, most notably with the EESSI project that originated in Europe.

I will describe our setup and discuss the pros and cons of Nix versus Gentoo Prefix, and the challenges that come with using glibc in a non-standard location.