Remote Builds

Nix supports remote builds, where a local Nix installation can forward Nix builds to other machines. This allows multiple builds to be performed in parallel and allows Nix to perform multi-platform builds in a semi-transparent way. For instance, if you perform a build for a x86_64-darwin on an i686-linux machine, Nix can automatically forward the build to a x86_64-darwin machine, if available.

To forward a build to a remote machine, it’s required that the remote machine is accessible via SSH and that it has Nix installed. You can test whether connecting to the remote Nix instance works, e.g.

$ nix store ping --store ssh://mac

will try to connect to the machine named mac. It is possible to specify an SSH identity file as part of the remote store URI, e.g.

$ nix store ping --store ssh://mac?ssh-key=/home/alice/my-key

Since builds should be non-interactive, the key should not have a passphrase. Alternatively, you can load identities ahead of time into ssh-agent or gpg-agent.

If you get the error

bash: nix-store: command not found
error: cannot connect to 'mac'

then you need to ensure that the PATH of non-interactive login shells contains Nix.

The list of remote build machines can be specified on the command line or in the Nix configuration file. For example, the following command allows you to build a derivation for x86_64-darwin on a Linux machine:

$ uname

$ nix build --impure \
  --expr '(with import <nixpkgs> { system = "x86_64-darwin"; }; runCommand "foo" {} "uname > $out")' \
  --builders 'ssh://mac x86_64-darwin'
[1/0/1 built, 0.0 MiB DL] building foo on ssh://mac

$ cat ./result

It is possible to specify multiple build machines separated by a semicolon or a newline, e.g.

  --builders 'ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd'

Remote build machines can also be configured in nix.conf, e.g.

builders = ssh://mac x86_64-darwin ; ssh://beastie x86_64-freebsd

Finally, remote build machines can be configured in a separate configuration file included in builders via the syntax @/path/to/file. For example,

builders = @/etc/nix/machines

causes the list of machines in /etc/nix/machines to be included. (This is the default.)