The version selection part sounds weird. The versions in nixpkgs make sense when you're running/building the system. If you're providing runtimes/compilers as a

The version selection part sounds weird. The versions in nixpkgs make sense when you're running/building the system. If you're providing runtimes/compilers as a platform, you really want something like what devenv does - provide the versions yourself. You really don't want to end up building an old system to provide an old nodejs - you're leaving security patches in dependencies behind. Devenv does it for example through https://github.com/cachix/nixpkgs-python https://github.com/cachix/nixpkgs-python "All Python versions, kept up-to-date on hourly basis using Nix." > Railway injects a deployment ID environment variable into all builds. They could've done it in the next layer after installation. Also, you can split packages into different layers. There's even automation for it if you need batches to keep the number of layers down.