1. You must read literally this entire README. It is critically important that you do so.
2. Open a PR adding yourself to users.nix.

I'll grant access to well known members of the community, and people well known members in the community trust.

TLDR: a trusted but malicious actor could hack your system through this builder. Do not use this builder for secret builds. Be careful what you use this system for. Do not trust the results. For a more nuanced understanding, read on.

For someone to use a server as a remote builder, they must be a trusted-user on the remote builder. man nix.conf has this to say about Trusted Users:

User that have additional rights when connecting to the Nix daemon, such as the ability to specify additional binary caches, or to import unsigned NARs.

Warning: The users listed here have the ability to compromise the security of a multi-user Nix store. For instance, they could install Trojan horses subsequently executed by other users. So you should consider carefully whether to add users to this list.

Nix's model of remote builders requires users to be able to directly import files in to the Nix store, and there is no guarantee what they import hasn't been maliciously modified.

The following is written as me, @winterqt:

I trust everyone who has access, but with limits:

1. DO NOT trust this builder for systems that contain private data or tools.

2. DO NOT trust this builder to make binary bootstrap tools, because we have to trust those bootstrap tools for a long time to not be compromised.

3. DO NOT trust this builder to make tools used to make binary bootstrap tools, because we have to trust those bootstrap tools for a long time to not be compromised.

IF YOU ARE: making binary bootstrap tools, please only use tools built by Hydra on a system which have never been exposed to things built from this server.

First, put this in your configuration.nix:

{
  programs.ssh.knownHosts."darwin-build-box.winter.cafe".publicKey =
    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIB0io9E0eXiDIEHvsibXOxOPveSjUPIr1RnNKbUkw3fD";

  nix = {
    distributedBuilds = true;
    buildMachines = [
      {
        hostName = "darwin-build-box.winter.cafe";
        maxJobs = 4;
        sshKey = "/root/a-private-key";
        sshUser = "your-user-name";
        systems = [ "aarch64-darwin" "x86_64-darwin" ];
      }
    ];
  };
}

Note: Make sure the SSH key specified above does not have a password, otherwise nix-build will give an error along the lines of:

unable to open SSH connection to 'ssh://[email protected]': cannot connect to '[email protected]'; trying other available machines...

Then run an initial SSH connection as root to setup the trust fingerprint:

$ sudo su
# ssh [email protected] -i /root/a-private-key

The fingerprint should always be:

ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIB0io9E0eXiDIEHvsibXOxOPveSjUPIr1RnNKbUkw3fD

If it is not, please open an issue!

Finally, nix-build . -A hello --argstr system aarch64-darwin.

If this doesn't work, reach out and I can help debug.

The hosting costs for this machine are paid for by the Nix 🖤 macOS Collective. If you'd like to support not only this machine but also toonn's work on the SDK bump, consider contributing.

• Domen Kožar, for running the Nix 🖤 macOS Collective.
• Graham Christensen, for running the aarch64 build box, where I took the structure of this README from.