You can easily share the Nix store of a machine via HTTP. This allows other machines to fetch store paths from that machine to speed up installations. It uses the same binary cache mechanism that Nix usually uses to fetch pre-built binaries from https://cache.nixos.org.
The daemon that handles binary cache requests via HTTP,
not part of the Nix distribution, but you can install it from Nixpkgs:
$ nix-env -iA nixpkgs.nix-serve
You can then start the server, listening for HTTP connections on whatever port you like:
$ nix-serve -p 8080
To check whether it works, try the following on the client:
$ curl http://avalon:8080/nix-cache-info
which should print something like:
StoreDir: /nix/store WantMassQuery: 1 Priority: 30
On the client side, you can tell Nix to use your binary cache using
--option extra-binary-caches, e.g.:
$ nix-env -iA nixpkgs.firefox --option extra-binary-caches http://avalon:8080/
extra-binary-caches tells Nix to use this binary cache in
addition to your default caches, such as https://cache.nixos.org.
Thus, for any path in the closure of Firefox, Nix will first check if
the path is available on the server
avalon or another binary caches.
If not, it will fall back to building from source.
You can also tell Nix to always use your binary cache by adding a line
nix.conf configuration file like this:
binary-caches = http://avalon:8080/ https://cache.nixos.org/