Topic: Modular Build — ESD build paths

The envisioned usage of the ESD includes:

• EBRAINS (jupyter) lab
• laptop use (i.e. run somewhere, use-as-downloaded or user-modified)
• HPC use (flat deployment or containerized, site-admin-managed or user-handled)
• service deployment (e.g., some k8s thing, or some classical systemd service)
• GDPR-sensitive environments (e.g., "minimum-set" deployments)

→ i.e. to avoid duplication in the build flow, we need a modular build path.

Several aspects are important:

• caching (sources, build results, spack buildcache, images)
• handling of filesystem locations
• restricted build environments (i.e. non-privileged to varying degree)

Spack defines a typical workflow that involves:

• concretization → finding out the packages that should be "there", in which version/variant, etc.)
• fetching of sources → downloading source packages that are to be built
• fetching and installing from buildcache → downloading and installing from a buildcache
• building and installing of packages from source
• (and environment creation/handling things (first step: base compiler, but also env definition/creation/spezialiation, etc.)