Thanks for the patience and help on this subject. Serving the tarballs as a hashed-mirror using ngnix did work for building small packages. It seems that every time busybox became involved in the build (which is more than you would think), the source was unable to be resolved.
I switched gears and decided to try for a full binary archive.
I think I finally understand this subject enough to understand previous posts on the topic. Perhaps I have complete cognitive dissidence in regards to this subject because it is so difficult to believe this problem isn’t solved.
I have been a software engineer for more than 30 years and somehow working Nix always makes me feel completely dumb. That isn’t to be taken as a slight against Nix, but perhaps as a slight against my own inability to adjust my way of thinking. Nix has so much potential. I am absolutely aghast that it isn’t the preferred solution world wide for so many things.
All of that said, the ability to be used completely offline/isolated/air-gapped is a critical piece that does not seem to have great support at this time.
The state of Nix Isolation and Airgapping
(Please correct the next paragraph if it is wrong)
For anyone researching this in the future, it should be understood that as of this time there is no foolproof solution to binary cache and even less so a source cache. There are some promising works that have been provided on the topic, but I have yet to find a complete working solution.
I first tried marsnix, since that has some record that it has been used successfully at least once. My thought was that if I could build a marsnix server, I could nix serve its packages. I was unable to get marsnix to work. It tried nix run with the github url; check out the repository and using nix-build, nix build, nix run; and several attempts at editing it to make it work.
“Nix in an Isolated Environment” is a post by a few nixers trying to achieve the same thing as me. Reading it now makes me feel irresponsible to be posting all of this again. The same questions were brought up by people who undoubtedly have more experience with Nix and they got further than I have been able to so far. I found out the hard way that it is important to read the entire thread before trying anything in the thread as you will find the problems that came out of each attempt and the proposed (if somewhat hacky) solutions. I am going to try the final solution listed there, but I was trying to use existing Ubuntu infrastructure to prepare a cache to build up NixOS and Nix packages and this solution will require me to start from a nix system first. This is not so much a problem as it requires me to rework my infrastructure a bit, meaning I will have to get a bit more lenience from my IT group to let me try this.
The Specific Mirroring Tool was mentioned in the “Nix In an Isolated Environment” post. Since the author was kind enough to let us know the documentation is outdated, it is difficult to know the level of completeness offered by this tool. I will be continuing to cheer on AleXoundOS, but it is unclear whether this work continues.
pete3n generated a repo for offline nix installer isos and discusses it in this thread. It is unclear whether this dependency list can be made large enough to support an offline for an extended period, but this warrants a look.
Additional paths from reponses below:
More Information Requested
If I have missed any ongoing efforts to provide isolated/offline/airgapped support for a nix mirror or nix systems, please let me know and I will try to include them in this list. If anyone has specific success with any of these, also please let me know.