Serving a Nix store via HTTP - Lix Reference Manual

# Serving a Nix store via HTTP

FIXME(Lix): This section documents outdated practices.

In particular, the Lix developers would not recommend using `nix-serve` as it is relatively-unmaintained Perl. The Lix developers would recommend instead using an s3 based cache (which is what https://cache.nixos.org is), and if it is desired to self-host it, use something like garage.

See the following projects:

- attic - multi-tenant cache for larger deployments, using s3 as a backend.
- harmonia - closer to a drop in replacement for use cases served by nix-serve

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 Lix usually uses to fetch pre-built binaries from https://cache.nixos.org.

The daemon that handles binary cache requests via HTTP, `nix-serve`, is not part of the Nix distribution, but you can install it from Nixpkgs:

    $ nix-env --install --attr 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 Lix to use your binary cache using `--substituters` (assuming you are a trusted user, see `trusted-users` in nix.conf), e.g.:

    $ nix-env --install --attr nixpkgs.firefox --substituters http://avalon:8080/

The option `substituters` tells Lix 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, Lix 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 Lix to always use your binary cache by adding a line to the `nix.conf` configuration file like this:

    substituters = http://avalon:8080/ https://cache.nixos.org/