Reproducibility is a key requirement to scientific development. Any scientific process, including software simulations, must be able to be replicated in order to prove the robustness of its process and the validity of its results. If an approach based on the extensive documentation of the process itself maybe considered as sufficient to guarantee reproducibility of results in domains like Physics or Biology, such a requirement proves to be incomplete for software being executed on high performance computing platforms. The specifics of the customized and exotic HPC architectures, the fast evolution of the software development environment as well as the various variables that can pollute the software development and building process are just few of the many possible sources of scientific result corruption. We describe in this paper how the developers of the Blue Brain Project built a software development ecosystem based on the Nix packaging and build system in order to guarantee the full portability, traceability and reproducibility of scientific results.