I must have misunderstood the talk a bit then, as I was under the impression you only upload a subset of the top-level, but I guess that’s just the subset of all the changes, which is what nixos-rebuild’s ssh things do too.
Right, we do our own delta of the changes and upload only that. Currently, it looks similar to the SSH copy but all is computed on ground. In the future, we could optimize things even further by doing bit by bit differences between the old and new paths and only upload the difference and get crazy small update packages. But, since we only update a few times a year if the upload size is not perfectly optimized, it still is good enough and we’ve put efforts elsewhere for now.
Guess you’re not planning on doing full OS upgrades then, considering how much data that would be?
We are definitely not going to upgrade the NixOS version, for each satellite we’re planning of having a pinned version of nixpkgs so that we avoid unexpected changes, and we can backport things as needed.