[j1elo]

Would that work, though?

I've never looked seriously into it, but my feeling is that distros will delete old versions as newer ones are uploaded: When I run "apt-cache policy git" in my Ubuntu, I only see a couple versions available to install, often other packages show only a single one (so, the latest).

[happymellon]

I know that Debian has Snapshot for older packages but you are still at the will of other people and people are fickle, and Nix should allow you to use specific versions to build your base images from to pin to.

However, much in the same way that if you actually take your build system seriously you'll store your application dependencies in a local proxy, you can run a mirror or proxy to hold these historical packages too.

Take a look at something like apt cacher, however it is a proxy cache so you can reproduce builds using the exact same package versions but if upstream delete old packages, and you want to roll back to one you haven't previously downloaded, then you are out of luck.